Sowing Depth Effects on Vetch Yield in Maragheh Dry Lands

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J Asghari Meidany

2013-12-01

Full Text Available Increases forage production and economic production in rainfed condition requires attention to agricultural issues such as determination of appropriate sowing depth. So in order to determine the effect of different sowing depths of vetch this experiment was conducted in Agricultural Research Station of Maragheh as strip plot based on randomized complete block design with three species of vetch V. sativa , V. dasycarpa-kouhak and V. narbonensis velox67 as main plots and three sowing depth as sub factor. Results showed that the effect of sowing depth on Vicia yield was significant at the 1% level and the maximum yield of wet hay, dry hay, straw and seed depth of belong to 8-10 cm depth and respectively are 5.364, 3.416, 4.389 and 1.081 ton per ha whereas the minimum yield of wet hay, dry hay, straw and seed depth of belong to 2-4 cm depth and respectively are 4.888, 2.318, 3.729 and 0.825. Among the three Vicia species the highest yield of wet hay, dry hay , straw and seed belongs to V. dasykarpa and respectively are 5.632, 3.532, 4.614 and 1.065 ton/ha. Soil moisture study in the field of these vetches at the time of 10 % vetch flowering showed water differences. V.dasycarpa had lower water depletion from soil. The amount of average soil water for species included: V. dasycarpa 26.31, V. sativa 23.76 and V. narbonesis 22.5.

Effect of {sup 15}n-labeled hairy vetch and nitrogen fertilization on maize nutrition and yield under no-tillage

Energy Technology Data Exchange (ETDEWEB)

Almeida Acosta, Jose Alan de [Drakkar Solos, Santa Maria, RS (Brazil); Amado, Telmo Jorge Carneiro; Silva, Leandro Souza da, E-mail: tamado@smail.ufsm.b, E-mail: leandro@smail.ufsm.b [Universidade Federal de Santa Maria (UFSM), RS (Brazil). Soil Dept.; Neergaard, Andreas de; Vinther, Mads, E-mail: adn@life.ku.d [University of Copenhagen (Denmark); Silveira Nicoloso, Rodrigo da, E-mail: rodrigo.nicoloso@cnpsa.embrapa.b [Embrapa Swine and Poultry, Concordia, SC (Brazil)

2011-07-15

This study evaluated the effect of hairy vetch (Vicia villosa Roth) as cover crop on maize nutrition and yield under no tillage using isotope techniques. For this purpose, three experiments were carried out: quantification of biological nitrogen fixation (BNF) in hairy vetch; estimation of the N release rate from hairy vetch residues on the soil surface; quantification of {sup 15}N recovery by maize from labeled hairy vetch under three rates of mineral N fertilization. This two year field experiment was conducted on a sandy Acrisol (FAO soil classification) or Argissolo Vermelho distrofico arenico (Brazilian Soil Classification), at a mean annual temperature of 18 deg C and mean annual rainfall of 1686 mm. The experiment was arranged in a double split-plot factorial design with three replications. Two levels of hairy vetch residue (50 and 100 % of the aboveground biomass production) were distributed on the surface of the main plots (5 x 12 m). Maize in the sub-plots (5 x 4 m) was fertilized with three N rates (0, 60, and 120 kg ha{sup -1} N), with urea as N source. The hairy vetch-derived N recovered by maize was evaluated in microplots (1.8 x 2.2 m). The BFN of hairy vetch was on average 72.4 %, which represents an annual input of 130 kg ha{sup -1} of atmospheric N. The N release from hairy vetch residues was fast, with a release of about 90 % of total N within the first four weeks after cover crop management and soil residue application. The recovery of hairy vetch {sup 15}N by maize was low, with an average of 12.3 % at harvest. Although hairy vetch was not directly the main source of maize N nutrition, the crop yield reached 8.2 Mg ha{sup -1}, without mineral fertilization. There was an apparent synergism between hairy vetch residue application and the mineral N fertilization rate of 60 kg ha{sup -1}, confirming the benefits of the combination of organic and inorganic N sources for maize under no tillage. (author)

Genetic Similarity between Cotton Leafroll Dwarf Virus and Chickpea Stunt Disease Associated Virus in India

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Arup Kumar Mukherjee

2016-12-01

Full Text Available The cotton leafroll dwarf virus (CLRDV is one of the most devastating pathogens of cotton. This malady, known as cotton blue disease, is widespread in South America where it causes huge crop losses. Recently the disease has been reported from India. We noticed occurrence of cotton blue disease and chickpea stunt disease in adjoining cotton and chickpea fields and got interested in knowing if these two viral diseases have some association. By genetic studies, we have shown here that CLRDV is very close to chickpea stunt disease associated virus (CpSDaV. We were successful in transmitting the CLRDV from cotton to chickpea. Our studies indicate that CpSDaV and CLRDV in India are possibly two different strains of the same virus. These findings would be helpful in managing these serious diseases by altering the cropping patterns.

Dinitrogen fixation estimates in Vetch-barley swards using {sup 15} N-methodology

Energy Technology Data Exchange (ETDEWEB)

Kurdali, F; Sharabi, N E [Atomic Energy Commission, P.O.Box 6091, Damascus, (Syrian Arab Republic)

1995-10-01

N 2- fixation in vetch (Vicia Sativa) grown alone and in mixture with barley (hordeum vulgare) in pots was evaluated using {sup 15} N isotope dilution method. Two harvests were made over the growing season. The proportion of the above-ground N, derived from atmospheric N 2 (% Ndfa) in mixed vetch was significantly higher than that of vetch in pure culture for the different harvests. However, this increase was not accompanied with the amount of N 2-fixation. On the other hand, no significant differences were observed in N-content or in N-derived from soil between barley grown in mixture and in monoculture, in spite of the difference in the number of plants between the tow cropping systems. These results indicate a high competing capacity of barley for soil nitrogen in mixed culture. Barley grown together with vetch had lower atom % 15 N excess than barley grown in mono-culture because it may have received some of their N from N-released by the legume in the second herbage but not in the first. Overall, results obtained from this experiment indicate the importance of mixed crops for forage production. Based on these results, further investigation must carried out in the field. 1 fig.

SUPPLEMENTARY VALUE OF VETCH (VICIA DASYCARPA) HAY ...

African Journals Online (AJOL)

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on feed intake and digestibility as well as milk production and composition in lactating F1 crossbred. (Boran x Friesian) cows fed .... the start of the experiment. The calves were separated from their dams five days after parturition. Experimental feeds. Vetch was harvested at 50% flowering, field cured, baled and stored in a ...

Genomic and phylogenetic evidence that Maize rough dwarf and Rice black-streaked dwarf fijiviruses should be classified as different geographic strains of a single species.

Science.gov (United States)

Xie, L; Lv, M-F; Yang, J; Chen, J-P; Zhang, H-M

Maize rough dwarf disease (MRDD) has long been known as one of the most devastating viral diseases of maize worldwide and is caused by single or complex infection by four fijiviruses: Maize rough dwarf virus (MRDV) in Europe and the Middle East, Mal de Rio Cuarto virus (MRCV) in South America, rice black-streaked dwarf virus (RBSDV), and Southern rice black-streaked dwarf virus (SRBSDV or Rice black-streaked dwarf virus 2, RBSDV-2) in East Asia. These are currently classified as four distinct species in the genus Fijivirus, family Reoviridae, but their taxonomic status has been questioned. To help resolve this, the nucleotide sequences of the ten genomic segments of an Italian isolate of MRDV have been determined, providing the first complete genomic sequence of this virus. Its genome has 29144 nucleotides and is similar in organization to those of RBSDV, SRBSDV, and MRCV. The 13 ORFs always share highest identities (81.3-97.2%) with the corresponding ORFs of RBSDV and phylogenetic analyses of the different genome segments and ORFs all confirm that MRDV clusters most closely with RBSDV and that MRCV and SRBSDV are slightly more distantly related. The results suggest that MRDV and RBSDV should be classified as different geographic strains of the same virus species and we suggest the name cereal black-streaked dwarf fijivirus (CBSDV) for consideration.

Simultaneous Detection of Mixed Infection of Onion yellow dwarf virus and an Allexivirus in RT-PCR for Ensuring Virus Free Onion Bulbs.

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Kumar, Sandeep; Baranwal, V K; Joshi, Subodh; Arya, Meenakshi; Majumder, S

2010-06-01

Reduced seed production in onion is associated with Onion yellow dwarf virus (OYDV), a filamentous Potyvirus. Onion is also infected with other filamentous virus particles suspected to be Allexivirus. RT-PCR was used to detect mixed infection of both the viruses in leaves and bulbs. A duplex RT-PCR was developed, which simultaneously detected the presence of these two viruses in winter (Rabi) onion bulb. In summer (Kharif) onion bulbs only Allexivirus was detected. The absence of OYDV in summer crop is discussed. The sequencing of RT-PCR amplified products confirmed the identity of OYDV and Allexivirus, the latter showing closer identity to Garlic virus C (GVC)/Garlic mite-borne mosaic virus. This makes the first detection of an Allexivirus in onion crop in India. The duplex RT-PCR to detect these viruses (OYDV and Allexivirus) would be an improvement for indexing of viruses in onion bulbs for seed production.

First report of a resistance-breaking strain of Raspberry bushy dwarf virus in red raspberry (Rubus idaeus) in North America

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Raspberry bushy dwarf virus (RBDV) is pollen-transmitted and the most important virus of Rubus worldwide. Infection of RBDV is associated with drupelet abortion, resulting in crumbly fruit. Multiple RBDV strains have been reported, with the Scottish-type (D200) strains being the most prevalent, and...

The complete genome sequence of a virus associated with cotton blue disease, cotton leafroll dwarf virus, confirms that it is a new member of the genus Polerovirus.

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Distéfano, Ana J; Bonacic Kresic, Ivan; Hopp, H Esteban

2010-11-01

Cotton blue disease is the most important virus disease of cotton in the southern part of America. The complete nucleotide sequence of the ssRNA genome of the cotton blue disease-associated virus was determined for the first time. It comprised 5,866 nucleotides, and the deduced genomic organization resembled that of members of the genus Polerovirus. Sequence homology comparison and phylogenetic analysis confirm that this virus (previous proposed name cotton leafroll dwarf virus) is a member of a new species within the genus Polerovirus.

Structural plasticity of Barley yellow dwarf virus-like cap-independent translation elements in four genera of plant viral RNAs.

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Wang, Zhaohui; Kraft, Jelena J; Hui, Alice Y; Miller, W Allen

2010-06-20

The 3' untranslated regions (UTRs) of many plant viral RNAs contain cap-independent translation elements (3' CITEs). Among the 3' CITEs, the Barley yellow dwarf virus (BYDV)-like translation elements (BTEs) form a structurally variable and widely distributed group. Viruses in three genera were known to harbor 3' BTEs, defined by the presence of a 17-nt consensus sequence. To understand BTE function, knowledge of phylogenetically conserved structure is essential, yet the secondary structure has been determined only for the BYDV BTE. Here we show that Rose spring dwarf-associated luteovirus, and two viruses in a fourth genus, Umbravirus, contain functional BTEs, despite deviating in the 17nt consensus sequence. Structure probing by selective 2'-hydroxyl acylation and primer extension (SHAPE) revealed conserved and highly variable structures in BTEs in all four genera. We conclude that BTEs tolerate striking evolutionary plasticity in structure, while retaining the ability to stimulate cap-independent translation. Copyright (c) 2010 Elsevier Inc. All rights reserved.

Southern rice black-streaked dwarf virus: a white-backed planthopper transmitted fijivirus threadening rice production in Asia

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Guohui eZhou

2013-09-01

Full Text Available Southern rice black-streaked dwarf virus (SRBSDV, a nonenveloped icosahedral virus with a genome of 10 double-stranded RNA segments, is a novel species in the genus Fijivirus (family Reoviridae first recognized in 2008. Rice plants infected with this virus exhibit symptoms similar to those caused by Rice black-streaked dwarf virus. Since 2009, the virus has rapidly spread and caused serious rice losses in East and Southeast Asia. Significant progress has been made in recent years in understanding this disease, especially about the functions of the viral genes, rice–virus–insect interactions, and epidemiology and control measures. The virus can be efficiently transmitted by the white-backed planthopper (WBPH, Sogatella furcifera in a persistent circulative propagative manner but cannot be transmitted by the brown planthopper (Nilaparvata lugens and small brown planthopper (Laodelphax striatellus. Rice, maize, Chinese sorghum (Coix lacryma-jobi and other grass weeds can be infected via WBPH. However, only rice plays a major role in the virus infection cycle because of the vector's preference. In Southeast Asia, WBPH is a long-distance migratory rice pest. The disease cycle can be described as follows: SRBSDV and its WBPH vector overwinter in warm tropical or sub-tropical areas; viruliferous WBPH adults carry the virus from south to north via long-distance migration in early spring, transmit the virus to rice seedlings in the newly colonized areas, and lay eggs on the infected seedlings; the next generation of WBPHs propagate on infected seedlings, become viruliferous, disperse, and cause new disease outbreaks. Several molecular and serological methods have been developed to detect SRBSDV in plant tissues and individual insects. Control measures based on protection from WBPH, including seedbed coverage, chemical seed treatments, and chemical spraying of seedlings, have proven effective in China.

Transcriptome Analysis of Two Vicia sativa Subspecies: Mining Molecular Markers to Enhance Genomic Resources for Vetch Improvement

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Tae-Sung Kim

2015-11-01

Full Text Available The vetch (Vicia sativa is one of the most important annual forage legumes globally due to its multiple uses and high nutritional content. Despite these agronomical benefits, many drawbacks, including cyano-alanine toxin, has reduced the agronomic value of vetch varieties. Here, we used 454 technology to sequence the two V. sativa subspecies (ssp. sativa and ssp. nigra to enrich functional information and genetic marker resources for the vetch research community. A total of 86,532 and 47,103 reads produced 35,202 and 18,808 unigenes with average lengths of 735 and 601 bp for V. sativa sativa and V. sativa nigra, respectively. Gene Ontology annotations and the cluster of orthologous gene classes were used to annotate the function of the Vicia transcriptomes. The Vicia transcriptome sequences were then mined for simple sequence repeat (SSR and single nucleotide polymorphism (SNP markers. About 13% and 3% of the Vicia unigenes contained the putative SSR and SNP sequences, respectively. Among those SSRs, 100 were chosen for the validation and the polymorphism test using the Vicia germplasm set. Thus, our approach takes advantage of the utility of transcriptomic data to expedite a vetch breeding program.

Barley yellow dwarf virus in barley crops in Tunisia: prevalence and molecular characterization

OpenAIRE

Asma NAJAR; Imen HAMDI; Arvind VARSANI

2017-01-01

A field survey was conducted in Tunisia in the North-Eastern regions (Bizerte, CapBon and Zaghouan), the North-Western region (Kef) and the Central-Eastern region (Kairouan) during the 2011/2012 growing season, in order to determine the incidence and the geographic distribution of Barley yellow dwarf virus (BYDVs) in barley fields. Tissue blot immunoassays (TBIA) showed that BYDV was most common in Zaghouan (incidence 14%), Cap Bon (14%) and Bizerte (35%), in randomly collected samples from t...

Analyses of pea necrotic yellow dwarf virus-encoded proteins.

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Krenz, Björn; Schießl, Ingrid; Greiner, Eva; Krapp, Susanna

2017-06-01

Pea necrotic yellow dwarf virus (PNYDV) is a multipartite, circular, single-stranded DNA plant virus. PNYDV encodes eight proteins and the function of three of which remains unknown-U1, U2, and U4. PNYDV proteins cellular localization was analyzed by GFP tagging and bimolecular fluorescence complementation (BiFC) studies. The interactions of all eight PNYDV proteins were tested pairwise in planta (36 combinations in total). Seven interactions were identified and two (M-Rep with CP and MP with U4) were characterized further. MP and U4 complexes appeared as vesicle-like spots and were localized at the nuclear envelope and cell periphery. These vesicle-like spots were associated with the endoplasmatic reticulum. In addition, a nuclear localization signal (NLS) was mapped for U1, and a mutated U1 with NLS disrupted localized at plasmodesmata and therefore might also have a role in movement. Taken together, this study provides evidence for previously undescribed nanovirus protein-protein interactions and their cellular localization with novel findings not only for those proteins with unknown function, but also for characterized proteins such as the CP.

Biomass production and nitrogen accumulation in pea, oat, and vetch green manure mixtures

International Nuclear Information System (INIS)

Jannink, J.L.; Liebman, M.; Merrick, L.C.

1996-01-01

Interest in the use of green manures has revived because of their role in improving soil quality and their beneficial N and non-N rotation effects. This study evaluated biomass production, N content, radiation interception (RI), and radiation use efficiency (RUE) of pea (Pisum sativum L.), oat (Avena sativa L.), and hairy vetch (Vicia villosa Roth) mixtures. Treatments were a three-way factorial of pea genotype ('Century' vs 'Tipu'), pea planting density (90 vs 224 kg ha -1 ), and cropping mixture (solecropped pea vs pea planted with a mixture of oat and hairy vetch). A mixture of oat and vetch without pea was also planted. Treatments were planted in early June on a Caribou gravelly loam (coarse-loamy, mixed, frigid Typic Haplorthods) in Presque Isle, ME, in 1993 and 1994. Biomass production and radiation interception were measured by repeated sampling. Mixture biomass was affected by a year x pea density interaction: respective yields for mixtures containing low-density and high-density pea were 770 and 880 g m -2 in 1993 vs 820 and 730 g m -2 in 1994. Mixture N content paralleled biomass production and averaged 209 g m -2 across all treatments. While pea sole crops did not consistently produce biomass or N equal to three-species mixtures the two-species mixture of oat and vetch did, yielding 820 g m -2 of biomass and 21.7 g m -2 of N, averaged over the 2 yr. Multiple regression showed that 61% of the variability in mixture biomass production was accounted for by a combination of early-season pea RI and midseason total mixture RUE. Economic analyses showed that rotation including these green manures may be economically competitive with a conventional rotation of barley (Hordeum vulgare L.) undersown with clover (Trifolium spp.) in a potato (Solanum tuberosum L.) production system

Transcriptional changes of rice in response to rice black-streaked dwarf virus.

Science.gov (United States)

Ahmed, Mohamed M S; Ji, Wen; Wang, Muyue; Bian, Shiquan; Xu, Meng; Wang, Weiyun; Zhang, Jiangxiang; Xu, Zhihao; Yu, Meimei; Liu, Qiaoquan; Zhang, Changquan; Zhang, Honggen; Tang, Shuzhu; Gu, Minghong; Yu, Hengxiu

2017-09-10

Rice black-streaked dwarf virus (RBSDV), a member of the genus Fijivirus in the family Reoviridae, causes significant economic losses in rice production in China and many other Asian countries. Although a great deal of effort has been made to elucidate the interactions among the virus, insect vectors, host and environmental conditions, few RBSDV proteins involved in pathogenesis have been identified, and the biological basis of disease development in rice remains largely unknown. Transcriptomic information associated with the disease development in rice would be helpful to unravel the biological mechanism. To determine how the rice transcriptome changes in response to RBSDV infection, we carried out RNA-Seq to perform a genome-wide gene expression analysis of a susceptible rice cultivar KTWYJ3. The transcriptomes of RBSDV-infected samples were compared to those of RBSDV-free (healthy) at two time points (time points are represented by group I and II). The results derived from the differential expression analysis in RBSDV-infected libraries vs. healthy ones in group I revealed that 102 out of a total of 281 significant differentially expressed genes (DEGs) were up-regulated and 179 DEGs were down-regulated. Of the 2592 identified DEGs in group II, 1588 DEGs were up-regulated and 1004 DEGs were down-regulated. A total of 66 DEGs were commonly identified in both groups. Of these 66 DEGs, expression patterns for 36 DEGs were similar in both groups. Our analysis demonstrated that some genes related to disease defense and stress resistance were up-regulated while genes associated with chloroplast were down-regulated in response to RBSDV infection. In addition, some genes associated with plant-height were differentially expressed. This result indicates those genes might be involved in dwarf symptoms caused by RBSDV. Taken together, our results provide a genome-wide transcriptome analysis for rice plants in response to RBSDV infection which may contribute to the

Inheritance of resistance to barley yellow dwarf virus detected by northern blot analysis

International Nuclear Information System (INIS)

Lorens, G.F.; Falk, B.W.; Qualset, C.O.

1989-01-01

Development of wheat (Triticum aestivum L.) cultivars tolerant to the barley yellow dwarf virus disease (BYD) has been limited by lack of precision in rating plants for response to infection, usually done by visual scoring of plant symptoms under field conditions. Other methodologies have been developed to study the host/pathogen relationship and to assess resistance or susceptibility. In this study northern dot blot analysis was used to determine barley yellow dwarf virus (BYDV) RNA concentrations of six wheat cultivars that differed in visual BYD symptom expression. Plants were infected with the NYPAV (PAV) isolate of BYDV in the greenhouse. At several dates after inoculation crude plant extracts were blotted on nitrocellulose and hybridized with a 32 P-labeled probe of the pPA8 cDNA clone of BYDV. The distribution of PRC for the F 2 population was compared to the distribution of BYD visual symptom scores for 403 F 2 plants of a similar F 2 population of NS 879/4 x Seri 82 under field conditions. The results were qualitatively similar, suggesting that northern dot blot analysis to measure PRC may be useful in understanding the genetics of resistance to BYD. This technique, when incorporated into breeding programs, could be important in the development of highly tolerant wheat cultivars with reduced losses to BYD

Early decomposer assemblages of soil organisms in litterbags with vetch and rye roots

DEFF Research Database (Denmark)

Georgieva, Slavka; Christensen, Søren; Petersen, Henning

2005-01-01

and predatory nematodes (the intraguild predator) protozoa (the intraguild prey) and bacteria (the common prey). The much higher fungal biomass in rye than in vetch litterbags was not reflected in the biomass of the fungal feeders. Due to the generally lower intrinsic rate of increase of the fungivores, as well...... as of the omnivores and predators, in comparison with the bacterial feeders, they were not able to generate dense populations at this early stage of decomposition....... relationship to flagellated protozoa. This suggests that these nematodes controlled the protozoan biomass constituting a lower fraction of the bacterivore biomass in vetch compared to in rye. Such intraguild predator-prey relationship is therefore indicated for microbivorous organisms among bacterivorous...

Low Temperature Storage of Southern Rice Black-Streaked Dwarf Virus-Infected Rice Plants Cannot Sustain Virus Transmission by the Vector.

Science.gov (United States)

Liu, Danfeng; Li, Pei; Han, Yongqiang; Lei, Wenbin; Hou, Maolin

2016-02-01

Southern rice black-streaked dwarf virus (SRBSDV) is a novel virus transmitted by white-backed planthopper Sogatella furcifera (Hováth) (Hemiptera: Delphacidae). Due to low virus transmission efficiency by the planthopper, researchers are frequently confronted with shortage of viruliferous vectors or infected rice plants, especially in winter and the following spring. To find new ways to maintain virus-infected materials, viral rice plants were stored at -80°C for 45 or 140 d and evaluated as virus sources in virus transmission by the vector. SRBSDV virions were not degraded during storage at -80°C as indicated by reverse transcription-polymerase chain reaction and reverse transcription real-time PCR detection. The planthopper nymphs fed on the infected thawed plants for 48 h survived at about 40% and showed positive detection of SRBSDV, but they lost the virus after feeding for another 20 d (the circulative transmission period) on noninfected plants. Transmission electron microscope images indicated broken capsid of virions in infected thawed leaves in contrast to integrity capsid of virions in infected fresh leaves. These results show that low temperature storage of SRBSDV-infected rice plants cannot sustain virus transmission by white-backed planthopper. © The Authors 2015. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

The rice dwarf virus P2 protein interacts with ent-kaurene oxidases in vivo, leading to reduced biosynthesis of gibberellins and rice dwarf symptoms.

Science.gov (United States)

Zhu, Shifeng; Gao, Feng; Cao, Xuesong; Chen, Mao; Ye, Gongyin; Wei, Chunhong; Li, Yi

2005-12-01

The mechanisms of viral diseases are a major focus of biology. Despite intensive investigations, how a plant virus interacts with host factors to cause diseases remains poorly understood. The Rice dwarf virus (RDV), a member of the genus Phytoreovirus, causes dwarfed growth phenotypes in infected rice (Oryza sativa) plants. The outer capsid protein P2 is essential during RDV infection of insects and thus influences transmission of RDV by the insect vector. However, its role during RDV infection within the rice host is unknown. By yeast two-hybrid and coimmunoprecipitation assays, we report that P2 of RDV interacts with ent-kaurene oxidases, which play a key role in the biosynthesis of plant growth hormones gibberellins, in infected plants. Furthermore, the expression of ent-kaurene oxidases was reduced in the infected plants. The level of endogenous GA1 (a major active gibberellin in rice vegetative tissues) in the RDV-infected plants was lower than that in healthy plants. Exogenous application of GA3 to RDV-infected rice plants restored the normal growth phenotypes. These results provide evidence that the P2 protein of RDV interferes with the function of a cellular factor, through direct physical interactions, that is important for the biosynthesis of a growth hormone leading to symptom expression. In addition, the interaction between P2 and rice ent-kaurene oxidase-like proteins may decrease phytoalexin biosynthesis and make plants more competent for virus replication. Moreover, P2 may provide a novel tool to investigate the regulation of GA metabolism for plant growth and development.

Exploiting Illumina Sequencing for the Development of 95 Novel Polymorphic EST-SSR Markers in Common Vetch (Vicia sativa subsp. sativa

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Zhipeng Liu

2014-05-01

Full Text Available The common vetch (Vicia sativa subsp. sativa, a self-pollinating and diploid species, is one of the most important annual legumes in the world due to its short growth period, high nutritional value, and multiple usages as hay, grain, silage, and green manure. The available simple sequence repeat (SSR markers for common vetch, however, are insufficient to meet the developing demand for genetic and molecular research on this important species. Here, we aimed to develop and characterise several polymorphic EST-SSR markers from the vetch Illumina transcriptome. A total number of 1,071 potential EST-SSR markers were identified from 1025 unigenes whose lengths were greater than 1,000 bp, and 450 primer pairs were then designed and synthesized. Finally, 95 polymorphic primer pairs were developed for the 10 common vetch accessions, which included 50 individuals. Among the 95 EST-SSR markers, the number of alleles ranged from three to 13, and the polymorphism information content values ranged from 0.09 to 0.98. The observed heterozygosity values ranged from 0.00 to 1.00, and the expected heterozygosity values ranged from 0.11 to 0.98. These 95 EST-SSR markers developed from the vetch Illumina transcriptome could greatly promote the development of genetic and molecular breeding studies pertaining to in this species.

Influence of Seeding Ratio, Planting Date, and Termination Date on Rye-Hairy Vetch Cover Crop Mixture Performance under Organic Management.

Science.gov (United States)

Lawson, Andrew; Cogger, Craig; Bary, Andy; Fortuna, Ann-Marie

2015-01-01

Cover crop benefits include nitrogen accumulation and retention, weed suppression, organic matter maintenance, and reduced erosion. Organic farmers need region-specific information on winter cover crop performance to effectively integrate cover crops into their crop rotations. Our research objective was to compare cover crop seeding mixtures, planting dates, and termination dates on performance of rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth) monocultures and mixtures in the maritime Pacific Northwest USA. The study included four seed mixtures (100% hairy vetch, 25% rye-75% hairy vetch, 50% rye-50% hairy vetch, and 100% rye by seed weight), two planting dates, and two termination dates, using a split-split plot design with four replications over six years. Measurements included winter ground cover; stand composition; cover crop biomass, N concentration, and N uptake; and June soil NO3(-)-N. Rye planted in mid-September and terminated in late April averaged 5.1 Mg ha(-1) biomass, whereas mixtures averaged 4.1 Mg ha(-1) and hairy vetch 2.3 Mg ha(-1). Delaying planting by 2.5 weeks reduced average winter ground cover by 65%, biomass by 50%, and cover crop N accumulation by 40%. Similar reductions in biomass and N accumulation occurred for late March termination, compared with late April termination. Mixtures had less annual biomass variability than rye. Mixtures accumulated 103 kg ha(-1) N and had mean C:N ratio rye, 97 kg ha(-1) for the mixtures, and 119 kg ha(-1) for hairy vetch. Weeds comprised less of the mixtures biomass (20% weeds by weight at termination) compared with the monocultures (29%). Cover crop mixtures provided a balance between biomass accumulation and N concentration, more consistent biomass over the six-year study, and were more effective at reducing winter weeds compared with monocultures.

The community ecology of barley/cereal yellow dwarf viruses in Western US grasslands.

Science.gov (United States)

Power, Alison G; Borer, Elizabeth T; Hosseini, Parviez; Mitchell, Charles E; Seabloom, Eric W

2011-08-01

Research on plant viruses in natural ecosystems has been increasing rapidly over the past decade. This paper reviews recent research on the barley and cereal yellow dwarf viruses (B/CYDVs) in grasslands of the western US, beginning with the evidence that the disease caused by these viruses facilitated the invasion of western US grasslands by European annual grasses. Observational and experimental studies of B/CYDVs were carried out along a latitudinal gradient (33.8-48.8°N) from southern California to southern Canada. The prevalence and community composition of B/CYDVs were assessed over a variety of scales and under a range of biotic and abiotic conditions. The findings indicate that both biotic and abiotic factors are important influences on virus ecology and epidemiology. Introduced annual grasses are high-quality hosts that amplify both virus and vector populations in this system, but our research suggests that endemic perennial grasses are critically important for sustaining virus populations in contemporary grasslands largely composed of introduced species. Experiments indicated that increased phosphorus supply to hosts resulted in greater host biomass and higher virus prevalence. Using experimental exclosures, it was found that the presence of grazing vertebrate herbivores increased the abundance of annual grasses, resulting in increased virus prevalence. The results of these studies suggest that patterns of B/CYDV prevalence and coinfection in western US grasslands are strongly shaped by the interactions of host plants, vectors, vertebrate herbivores, and abiotic drivers including nutrients. Copyright © 2011 Elsevier B.V. All rights reserved.

Impact of vetch cover crop on runoff, soil loss, soil chemical properties and yield of chickpea in North Gondar, Ethiopia

Science.gov (United States)

Demelash, Nigus; Klik, Andreas; Holzmann, Hubert; Ziadat, Feras; Strohmeier, Stefan; Bayu, Wondimu; Zucca, Claudio; Abera, Atikilt

2016-04-01

Cover crops improve the sustainability and quality of both natural system and agro ecosystem. In Gumara-Maksegnit watershed which is located in Lake Tana basin, farmers usually use fallow during the rainy season for the preceding chickpea production system. The fallowing period can lead to soil erosion and nutrient losses. A field experiment was conducted during growing seasons 2014 and 2015 to evaluate the effect of cover crops on runoff, soil loss, soil chemical properties and yield of chickpea in North Gondar, Ethiopia. The plot experiment contained four treatments arranged in Randomized Complete Block Design with three replications: 1) Control plot (Farmers' practice: fallowing- without cover crop), 2) Chickpea planted with Di-ammonium phosphate (DAP) fertilizer with 46 k ha-1 P2O5 and 23 k ha-1 nitrogen after harvesting vetch cover crop, 3) Chick pea planted with vetch cover crop incorporated with the soil as green manure without fertilizer, 4) Chick pea planted with vetch cover crop and incorporated with the soil as green manure and with 23 k ha-1 P2O5 and 12.5 k ha-1 nitrogen. Each plot with an area of 36 m² was equipped with a runoff monitoring system. Vetch (Vicia sativa L.) was planted as cover crop at the onset of the rain in June and used as green manure. The results of the experiment showed statistically significant (P plant, above ground biomass and grain yield of chick pea. However, there was no statistically significant difference (P > 0.05) on average plant height, average number of branches and hundred seed weight. Similarly, the results indicated that cover crop has a clear impact on runoff volume and sediment loss. Plots with vetch cover crop reduce the average runoff by 65% and the average soil loss decreased from 15.7 in the bare land plot to 8.6 t ha-1 with plots covered by vetch. In general, this result reveales that the cover crops, especially vetch, can be used to improve chickpea grain yield in addition to reduce soil erosion in the

The Rice Dwarf Virus P2 Protein Interacts with ent-Kaurene Oxidases in Vivo, Leading to Reduced Biosynthesis of Gibberellins and Rice Dwarf Symptoms1

Science.gov (United States)

Zhu, Shifeng; Gao, Feng; Cao, Xuesong; Chen, Mao; Ye, Gongyin; Wei, Chunhong; Li, Yi

2005-01-01

The mechanisms of viral diseases are a major focus of biology. Despite intensive investigations, how a plant virus interacts with host factors to cause diseases remains poorly understood. The Rice dwarf virus (RDV), a member of the genus Phytoreovirus, causes dwarfed growth phenotypes in infected rice (Oryza sativa) plants. The outer capsid protein P2 is essential during RDV infection of insects and thus influences transmission of RDV by the insect vector. However, its role during RDV infection within the rice host is unknown. By yeast two-hybrid and coimmunoprecipitation assays, we report that P2 of RDV interacts with ent-kaurene oxidases, which play a key role in the biosynthesis of plant growth hormones gibberellins, in infected plants. Furthermore, the expression of ent-kaurene oxidases was reduced in the infected plants. The level of endogenous GA1 (a major active gibberellin in rice vegetative tissues) in the RDV-infected plants was lower than that in healthy plants. Exogenous application of GA3 to RDV-infected rice plants restored the normal growth phenotypes. These results provide evidence that the P2 protein of RDV interferes with the function of a cellular factor, through direct physical interactions, that is important for the biosynthesis of a growth hormone leading to symptom expression. In addition, the interaction between P2 and rice ent-kaurene oxidase-like proteins may decrease phytoalexin biosynthesis and make plants more competent for virus replication. Moreover, P2 may provide a novel tool to investigate the regulation of GA metabolism for plant growth and development. PMID:16299167

Carbon balance assessment by eddy covariance method for agroecosystems with potato plants and oats & vetch mixture on sod-podzolic soils of Russia

Science.gov (United States)

Meshalkina, J. L.; Yaroslavtsev, A. M.; Vasenev, I. I.; Andreeva, I. V.; Tihonova, M. V.

2018-01-01

The carbon balance for the agroecosystems with potato plants and oats & vetch mixture on sod-podzolics soils was evaluated using the eddy covariance approach. Absorption of carbon was recorded only during the growing season; maximum values were detected for all crops in July. The number of days during the vegetation period, when the carbon stocked in the fields with potatoes and oats & vetch mixture was about the same and accounted for 53-55 days. During this period, the increase in gross primary production (GPP) is well correlated with the crop yields. The curve of the gross primary productivity is closely linked to the phases of development of plants; for potatoes, this graph differs significantly for all phases. Form of oats & vetch mixture biomass curve shown linear increases. Carbon losses were observed for all the studied agroecosystems: for fields with an oats & vetch mixture they were 254 g C m-2 y-1, while for fields with potato plants they were 307 g C m-2 y-1. Values about 250-300 g C m-2 per year may be considered as estimated values for the total carbon uptake for agroecosystems with potato plants and oats & vetch mixture on sod-podzolic soils.

Comparison of ELISA and RT-PCR for the detection of Prunus necrotic ring spot virus and prune dwarf virus in almond (Prunus dulcis).

Science.gov (United States)

Mekuria, Genet; Ramesh, Sunita A; Alberts, Evita; Bertozzi, Terry; Wirthensohn, Michelle; Collins, Graham; Sedgley, Margaret

2003-12-01

A technique based on the reverse transcriptase-polymerase chain reaction (RT-PCR) has been developed to detect the presence of Prunus necrotic ringspot virus (PNRSV) and prune dwarf virus (PDV) simultaneously in almond. This paper presents the results of a 3-year study comparing both enzyme-linked immunosorbent assay (ELISA) and RT-PCR for the detection of PNRSV and PDV using 175 almond leaf samples. Multiplex RT-PCR was found to be more sensitive than ELISA, especially when followed by nested PCR for the detection of PDV. The RT-PCR technique has the added advantage that plant material can be tested at any time throughout the growing season.

Developing methods of strip cropping cucumbers with rye/vetch

OpenAIRE

Ogutu, Maurice Okendo

2000-01-01

The purpose of this research carried out in 1998 and 1999 was to develop methods for strip cropping of cucumbers with rye/vetch and black plastic mulch. Effects of planting methods, weed control measures, and cover crop management techniques on pest and beneficial insects, petiole sap nitrate-nitrogen, soil moisture, yields and economic viability were assessed. Four treatments, namely cucumber direct seeded in black plastic mulch on tilled bare ground (conventional); cucumber d...

Influence of Seeding Ratio, Planting Date, and Termination Date on Rye-Hairy Vetch Cover Crop Mixture Performance under Organic Management.

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Andrew Lawson

Full Text Available Cover crop benefits include nitrogen accumulation and retention, weed suppression, organic matter maintenance, and reduced erosion. Organic farmers need region-specific information on winter cover crop performance to effectively integrate cover crops into their crop rotations. Our research objective was to compare cover crop seeding mixtures, planting dates, and termination dates on performance of rye (Secale cereale L. and hairy vetch (Vicia villosa Roth monocultures and mixtures in the maritime Pacific Northwest USA. The study included four seed mixtures (100% hairy vetch, 25% rye-75% hairy vetch, 50% rye-50% hairy vetch, and 100% rye by seed weight, two planting dates, and two termination dates, using a split-split plot design with four replications over six years. Measurements included winter ground cover; stand composition; cover crop biomass, N concentration, and N uptake; and June soil NO3(--N. Rye planted in mid-September and terminated in late April averaged 5.1 Mg ha(-1 biomass, whereas mixtures averaged 4.1 Mg ha(-1 and hairy vetch 2.3 Mg ha(-1. Delaying planting by 2.5 weeks reduced average winter ground cover by 65%, biomass by 50%, and cover crop N accumulation by 40%. Similar reductions in biomass and N accumulation occurred for late March termination, compared with late April termination. Mixtures had less annual biomass variability than rye. Mixtures accumulated 103 kg ha(-1 N and had mean C:N ratio <17:1 when planted in mid-September and terminated in late April. June soil NO3(--N (0 to 30 cm depth averaged 62 kg ha(-1 for rye, 97 kg ha(-1 for the mixtures, and 119 kg ha(-1 for hairy vetch. Weeds comprised less of the mixtures biomass (20% weeds by weight at termination compared with the monocultures (29%. Cover crop mixtures provided a balance between biomass accumulation and N concentration, more consistent biomass over the six-year study, and were more effective at reducing winter weeds compared with monocultures.

Genomic and proteomic analysis of Schizaphis graminum reveals cyclophilin proteins are involved in the transmission of cereal yellow dwarf virus.

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Cecilia Tamborindeguy

Full Text Available Yellow dwarf viruses cause the most economically important virus diseases of cereal crops worldwide and are transmitted by aphid vectors. The identification of aphid genes and proteins mediating virus transmission is critical to develop agriculturally sustainable virus management practices and to understand viral strategies for circulative movement in all insect vectors. Two cyclophilin B proteins, S28 and S29, were identified previously in populations of Schizaphisgraminum that differed in their ability to transmit the RPV strain of Cereal yellow dwarf virus (CYDV-RPV. The presence of S29 was correlated with F2 genotypes that were efficient virus transmitters. The present study revealed the two proteins were isoforms, and a single amino acid change distinguished S28 and S29. The distribution of the two alleles was determined in 12 F2 genotypes segregating for CYDV-RPV transmission capacity and in 11 genetically independent, field-collected S. graminum biotypes. Transmission efficiency for CYDV-RPV was determined in all genotypes and biotypes. The S29 isoform was present in all genotypes or biotypes that efficiently transmit CYDV-RPV and more specifically in genotypes that efficiently transport virus across the hindgut. We confirmed a direct interaction between CYDV-RPV and both S28 and S29 using purified virus and bacterially expressed, his-tagged S28 and S29 proteins. Importantly, S29 failed to interact with a closely related virus that is transported across the aphid midgut. We tested for in vivo interactions using an aphid-virus co-immunoprecipitation strategy coupled with a bottom-up LC-MS/MS analysis using a Q Exactive mass spectrometer. This analysis enabled us to identify a third cyclophilin protein, cyclophilin A, interacting directly or in complex with purified CYDV-RPV. Taken together, these data provide evidence that both cyclophilin A and B interact with CYDV-RPV, and these interactions may be important but not sufficient to mediate

Exogenously applied D-pinitol and D-chiro-inositol modifies the accumulation of α-D-galactosides in developing tiny vetch (Vicia hirsuta [L.] S.F. Gray seeds

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Lesław B. Lahuta

2011-01-01

Full Text Available In the present study we have investigated the effect of exogenous cyclitols on the accumulation of their galactosides and raffinose family oligosaccharides (RFOs, as well as on some enzymes important for their biosynthesis in seeds of tiny vetch (Vicia hirsuta [L.] S.F. Gray. Immature seeds during 6-day incubation with D-chiro-inositol (naturally does not appear in seeds of tiny vetch were accumulated cyclitol and its galactosides (fagopyritols: B1 and B2. Short 4-hour incubation with D-chiro-inositol, and subsequent slow desiccation process caused accumulation of free cyclitol only, without biosynthesis of its galactosides. Feeding D-chiro-inositol to pods of tiny vetch induced accumulation of high levels of its galactosides (fagopyritol B1, B2 and B3 in maturing seeds. Similarly, feeding D-pinitol increased accumulation of its mono-, di- and tri-galactosides: GPA, GPB, DGPA and TGPA in tiny vetch seed. Accumulation of both cyclitols and their galactosides drastically reduced accumulation of verbascose. Inhibition of RFOs biosynthesis by elevated levels of free cyclitols suggests some competition between formation of both types of galactosides and similarity of both biosynthetic routes in tiny vetch seeds. Galactinol synthase (GolS from tiny vetch seeds demonstrated ability to utilize D-chiro-inositol as galactosyl acceptor, instead of myo-inositol. Presence of both cyclitols, as substrates for GolS, caused synthesis of their galactosides: fagopyritol B1 and galactinol. However, formation of galactinol was more efficient than fagopyritol B1. D-chiro-Inositol and D-pinitol at concentrations several-fold higher than myo-inositol had inhibitory effect on GolS. Thus, we suggest that a level of free cyclitols can have an influence on the rate of galactinol biosynthesis and further accumulation of RFOs and galactosyl cyclitols in tiny vetch seeds.

Polycistronic artificial miRNA-mediated resistance to Wheat dwarf virus in barley is highly efficient at low temperature.

Science.gov (United States)

Kis, András; Tholt, Gergely; Ivanics, Milán; Várallyay, Éva; Jenes, Barnabás; Havelda, Zoltán

2016-04-01

Infection of Wheat dwarf virus (WDV) strains on barley results in dwarf disease, imposing severe economic losses on crop production. As the natural resistance resources against this virus are limited, it is imperative to elaborate a biotechnological approach that will provide effective and safe immunity to a wide range of WDV strains. Because vector insect-mediated WDV infection occurs during cool periods in nature, it is important to identify a technology which is effective at lower temperature. In this study, we designed artificial microRNAs (amiRNAs) using a barley miRNA precursor backbone, which target different conservative sequence elements of the WDV strains. Potential amiRNA sequences were selected to minimize the off-target effects and were tested in a transient sensor system in order to select the most effective constructs at low temperature. On the basis of the data obtained, a polycistronic amiRNA precursor construct (VirusBuster171) was built expressing three amiRNAs simultaneously. The construct was transformed into barley under the control of a constitutive promoter. The transgenic lines were kept at 12-15 °C to mimic autumn and spring conditions in which major WDV infection and accumulation take place. We were able to establish a stable barley transgenic line displaying resistance to insect-mediated WDV infection. Our study demonstrates that amiRNA technology can be an efficient tool for the introduction of highly efficient resistance in barley against a DNA virus belonging to the Geminiviridae family, and this resistance is effective at low temperature where the natural insect vector mediates the infection process. © 2015 BSPP and John Wiley & Sons Ltd.

Benefits of Vetch and Rye Cover Crops to Sweet Corn under No-Tillage

NARCIS (Netherlands)

Zotarelli, L.; Avila, L.; Scholberg, J.M.S.; Alves, B.J.R.

2009-01-01

Leguminous cover crops (CCs) may reduce N fertilizer requirements by fixing N biologically and storing leftover N-fertilizer applied in the previous year. The objective of this study was to determine the contribution of CCs [rye (Secale cereal L.) and hairy vetch (Vicia villosa Roth)] on plant N

Detection of yellow dwarf virus onion (OYDV) and garlic common latent virus (GCLV) in Costa Rican garlic (Allium sativum L)

International Nuclear Information System (INIS)

Guillen Watson, Anny Vannesa; Chacon Cerdas, Randall; Zuniga Vega, Claudia

2011-01-01

Viral diseases have been responsible for significant losses in crop yield of garlic in the world. Costa Rican material Garlic has been analyzed to determine the incidence of : onion yellow dwarf virus (OYDV), the leek yellow stripe virus (LYSV), shallot latent virus (SLV) and garlic common latent virus (GLCV). The DAS-ELISA technique has been used for status native plant material. Bulbs field apparently normal (N), normal with yellow tunic (TA) and deformed (D) and normal field sheets (N), symptomatic (S) and possible presence of viral vectors (VT) were used. Vitroplants product have analyzed the introduction of apices of 1,0 and 0,5 cm in length teeth from normal (N) and yellow tunic (TA). The 33% of the bulbs GCLV field were analyzed for positive (TA), whereas OYDV was detected 100% appearance regardless. 100% of the plantlets have presented without infection of GCLV, the OYDV only those introduced in apices of 1,0 cm from bulbs with yellow robes have shown without effect. GCLV is determined for 100% of the samples for both batches OYDV bulb formation in vitro and in only 50%. In the Costa Rican garlic has concluded that are present the viruses of GCLV and OYDV, with a high incidence on local material and differential infection according to the organ analyzed. Various methodologies combined are recommended together with the apexes vitro cultivation, for more effective viral clearance and thus increase the value and boost the local seed crop. (author) [es

Genome sequence variation in the constricta strain dramatically alters the protein interaction and localization map of Potato yellow dwarf virus

Science.gov (United States)

The genome sequence of the constricta strain of Potato yellow dwarf virus (CYDV) was determined to be 12,792 nucleotides long and organized into seven open reading frames with the gene order 3’-N-X-P-Y-M-G-L-5’, which encodes the nucleocapsid, phosphoprotein, movement, matrix, glycoprotein and RNA-d...

Overexpression of rice black-streaked dwarf virus p7-1 in Arabidopsis results in male sterility due to non-dehiscent anthers.

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Feng Sun

Full Text Available Rice black-streaked dwarf virus (RBSDV, a member of the genus Fijivirus in the family Reoviridae, is propagatively transmitted by the small brown planthopper (Laodelphax striatellus Fallén. RBSDV causes rice black-streaked dwarf and maize rough dwarf diseases, which lead to severe yield losses in crops in China. Although several RBSDV proteins have been studied in detail, the functions of the nonstructural protein P7-1 are still largely unknown. To investigate the role of the P7-1 protein in virus pathogenicity, transgenic Arabidopsis thaliana plants were generated in which the P7-1 gene was expressed under the control of the 35S promoter. The RBSDV P7-1-transgenic Arabidopsis plants (named P7-1-OE were male sterility. Flowers and pollen from P7-1-transgenic plants were of normal size and shape, and anthers developed to the normal size but failed to dehisce. The non-dehiscent anthers observed in P7-1-OE were attributed to decreased lignin content in the anthers. Furthermore, the reactive oxygen species levels were quite low in the transgenic plants compared with the wild type. These results indicate that ectopic expression of the RBSDV P7-1 protein in A. thaliana causes male sterility, possibly through the disruption of the lignin biosynthesis and H2O2-dependent polymerization pathways.

Overexpression of rice black-streaked dwarf virus p7-1 in Arabidopsis results in male sterility due to non-dehiscent anthers.

Science.gov (United States)

Sun, Feng; Yuan, Xia; Xu, Qiufang; Zhou, Tong; Fan, Yongjian; Zhou, Yijun

2013-01-01

Rice black-streaked dwarf virus (RBSDV), a member of the genus Fijivirus in the family Reoviridae, is propagatively transmitted by the small brown planthopper (Laodelphax striatellus Fallén). RBSDV causes rice black-streaked dwarf and maize rough dwarf diseases, which lead to severe yield losses in crops in China. Although several RBSDV proteins have been studied in detail, the functions of the nonstructural protein P7-1 are still largely unknown. To investigate the role of the P7-1 protein in virus pathogenicity, transgenic Arabidopsis thaliana plants were generated in which the P7-1 gene was expressed under the control of the 35S promoter. The RBSDV P7-1-transgenic Arabidopsis plants (named P7-1-OE) were male sterility. Flowers and pollen from P7-1-transgenic plants were of normal size and shape, and anthers developed to the normal size but failed to dehisce. The non-dehiscent anthers observed in P7-1-OE were attributed to decreased lignin content in the anthers. Furthermore, the reactive oxygen species levels were quite low in the transgenic plants compared with the wild type. These results indicate that ectopic expression of the RBSDV P7-1 protein in A. thaliana causes male sterility, possibly through the disruption of the lignin biosynthesis and H2O2-dependent polymerization pathways.

Selected aspects of tiny vetch [Vicia hirsuta (L. Gray S.F.] seed ecology: generative reproduction and effects of seed maturity and seed storage on seed germination

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Magdalena Kucewicz

2012-12-01

Full Text Available Vicia hirsuta (L. Gray S.F. (tiny vetch is a common and persistent segetal weed. Tiny vetch seeds and pods reach different stages of maturity during the crop harvest season. Some seeds that mature before cereal harvest are shed in the field and deposited in the soil seed bank, while others become incorporated into seed material. The objective of this study was to describe selected aspects of tiny vetch seed ecology: to determine the rate of individual reproduction of vetch plants growing in winter and spring grain crops and to evaluate the germination of seeds at different stages of maturity, subject to storage conditions. The seeds and pods of V. hirsuta were sorted according to their development stages at harvest and divided into two groups. The first group was stored under laboratory conditions for two months. In the autumn of the same year, the seeds were subjected to germination tests. The remaining seeds were stored in a storeroom, and were planted in soil in the spring. The germination rate was evaluated after 8 months of storage. Potential productivity (developed pods and flowers, fruit buds was higher in plants fruiting in winter wheat than in spring barley. Vetch plants produced around 17-26% more pods (including cracked, mature, greenish-brown and green pods and around 25% less buds in winter wheat than in spring barley. Immature seeds were characterized by the highest germination capacity. Following storage under laboratory conditions and stratification in soil, mature seeds germinated at a rate of several percent. After storage in a storeroom, seeds at all three development stages broke dormancy at a rate of 72- 75%. The high germination power of tiny vetch seeds stored in a storeroom indicates that this plant can be classified as an obligatory speirochoric weed species.

Genome-Wide Association Mapping of Barley Yellow Dwarf Virus Tolerance in Spring Oat (Avena sativa L..

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Bradley J Foresman

Full Text Available Barley yellow dwarf viruses (BYDVs are responsible for the disease barley yellow dwarf (BYD and affect many cereals including oat (Avena sativa L.. Until recently, the molecular marker technology in oat has not allowed for many marker-trait association studies to determine the genetic mechanisms for tolerance. A genome-wide association study (GWAS was performed on 428 spring oat lines using a recently developed high-density oat single nucleotide polymorphism (SNP array as well as a SNP-based consensus map. Marker-trait associations were performed using a Q-K mixed model approach to control for population structure and relatedness. Six significant SNP-trait associations representing two QTL were found on chromosomes 3C (Mrg17 and 18D (Mrg04. This is the first report of BYDV tolerance QTL on chromosome 3C (Mrg17 and 18D (Mrg04. Haplotypes using the two QTL were evaluated and distinct classes for tolerance were identified based on the number of favorable alleles. A large number of lines carrying both favorable alleles were observed in the panel.

Assessment of reference gene stability in Rice stripe virus and Rice black streaked dwarf virus infection rice by quantitative Real-time PCR.

Science.gov (United States)

Fang, Peng; Lu, Rongfei; Sun, Feng; Lan, Ying; Shen, Wenbiao; Du, Linlin; Zhou, Yijun; Zhou, Tong

2015-10-24

Stably expressed reference gene(s) normalization is important for the understanding of gene expression patterns by quantitative Real-time PCR (RT-qPCR), particularly for Rice stripe virus (RSV) and Rice black streaked dwarf virus (RBSDV) that caused seriously damage on rice plants in China and Southeast Asia. The expression of fourteen common used reference genes of Oryza sativa L. were evaluated by RT-qPCR in RSV and RBSDV infected rice plants. Suitable normalization reference gene(s) were identified by geNorm and NormFinder algorithms. UBQ 10 + GAPDH and UBC + Actin1 were identified as suitable reference genes for RT-qPCR normalization under RSV and RBSDV infection, respectively. When using multiple reference genes, the expression patterns of OsPRIb and OsWRKY, two virus resistance genes, were approximately similar with that reported previously. Comparatively, by using single reference gene (TIP41-Like), a weaker inducible response was observed. We proposed that the combination of two reference genes could obtain more accurate and reliable normalization of RT-qPCR results in RSV- and RBSDV-infected plants. This work therefore sheds light on establishing a standardized RT-qPCR procedure in RSV- and RBSDV-infected rice plants, and might serve as an important point for discovering complex regulatory networks and identifying genes relevant to biological processes or implicated in virus.

Biomass decomposition and nutrient release from black oat and hairy vetch residues deposited in a vineyard

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Paulo Ademar Avelar Ferreira

2014-10-01

Full Text Available A significant quantity of nutrients in vineyards may return to the soil each year through decomposition of residues from cover plants. This study aimed to evaluate biomass decomposition and nutrient release from residues of black oats and hairy vetch deposited in the vines rows, with and without plastic shelter, and in the between-row areas throughout the vegetative and productive cycle of the plants. The study was conducted in a commercial vineyard in Bento Gonçalves, RS, Brazil, from October 2008 to February 2009. Black oat (Avena strigosa and hairy vetch (Vicia villosa residues were collected, subjected to chemical (C, N, P, K, Ca, and Mg and biochemical (cellulose - Cel, hemicellulose - Hem, and lignin - Lig content analyses, and placed in litter bags, which were deposited in vines rows without plastic shelter (VPRWS, in vines rows with plastic shelter (VPRS, and in the between-row areas (BR. We collected the residues at 0, 33, 58, 76, and 110 days after deposition of the litter bags, prepared the material, and subjected it to analysis of total N, P, K, Ca, and Mg content. The VPRS contained the largest quantities and percentages of dry matter and residual nutrients (except for Ca in black oat residues from October to February, which coincides with the period from flowering up to grape harvest. This practice led to greater protection of the soil surface, avoiding surface runoff of the solution derived from between the rows, but it retarded nutrient cycling. The rate of biomass decomposition and nutrient release from hairy vetch residues from October to February was not affected by the position of deposition of the residues in the vineyard, which may especially be attributed to the lower values of the C/N and Lig/N ratios. Regardless of the type of residue, black oat or hairy vetch, the greatest decomposition and nutrient release mainly occurred up to 33 days after deposition of the residues on the soil surface, which coincided with the

The 3' untranslated region of tobacco necrosis virus RNA contains a barley yellow dwarf virus-like cap-independent translation element.

Science.gov (United States)

Shen, Ruizhong; Miller, W Allen

2004-05-01

RNAs of many viruses are translated efficiently in the absence of a 5' cap structure. The tobacco necrosis virus (TNV) genome is an uncapped, nonpolyadenylated RNA whose translation mechanism has not been well investigated. Computational analysis predicted a cap-independent translation element (TE) within the 3' untranslated region (3' UTR) of TNV RNA that resembles the TE of barley yellow dwarf virus (BYDV), a luteovirus. Here we report that such a TE does indeed exist in the 3' UTR of TNV strain D. Like the BYDV TE, the TNV TE (i) functions both in vitro and in vivo, (ii) requires additional sequence for cap-independent translation in vivo, (iii) has a similar secondary structure and the conserved sequence CGGAUCCUGGGAAACAGG, (iv) is inactivated by a four-base duplication in this conserved sequence, (v) can function in the 5' UTR, and (vi) when located in its natural 3' location, may form long-distance base pairing with the viral 5' UTR that is conserved and probably required. The TNV TE differs from the BYDV TE by having only three helical domains instead of four. Similar structures were found in all members of the Necrovirus genus of the Tombusviridae family, except satellite tobacco necrosis virus, which harbors a different 3' cap-independent translation domain. The presence of the BYDV-like TE in select genera of different families indicates that phylogenetic distribution of TEs does not follow standard viral taxonomic relationships. We propose a new class of cap-independent TE called BYDV-like TE.

Hairpin RNA Targeting Multiple Viral Genes Confers Strong Resistance to Rice Black-Streaked Dwarf Virus

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Fangquan Wang

2016-05-01

Full Text Available Rice black-streaked dwarf virus (RBSDV belongs to the genus Fijivirus in the family of Reoviridae and causes severe yield loss in rice-producing areas in Asia. RNA silencing, as a natural defence mechanism against plant viruses, has been successfully exploited for engineering virus resistance in plants, including rice. In this study, we generated transgenic rice lines harbouring a hairpin RNA (hpRNA construct targeting four RBSDV genes, S1, S2, S6 and S10, encoding the RNA-dependent RNA polymerase, the putative core protein, the RNA silencing suppressor and the outer capsid protein, respectively. Both field nursery and artificial inoculation assays of three generations of the transgenic lines showed that they had strong resistance to RBSDV infection. The RBSDV resistance in the segregating transgenic populations correlated perfectly with the presence of the hpRNA transgene. Furthermore, the hpRNA transgene was expressed in the highly resistant transgenic lines, giving rise to abundant levels of 21–24 nt small interfering RNA (siRNA. By small RNA deep sequencing, the RBSDV-resistant transgenic lines detected siRNAs from all four viral gene sequences in the hpRNA transgene, indicating that the whole chimeric fusion sequence can be efficiently processed by Dicer into siRNAs. Taken together, our results suggest that long hpRNA targeting multiple viral genes can be used to generate stable and durable virus resistance in rice, as well as other plant species.

Hairpin RNA Targeting Multiple Viral Genes Confers Strong Resistance to Rice Black-Streaked Dwarf Virus.

Science.gov (United States)

Wang, Fangquan; Li, Wenqi; Zhu, Jinyan; Fan, Fangjun; Wang, Jun; Zhong, Weigong; Wang, Ming-Bo; Liu, Qing; Zhu, Qian-Hao; Zhou, Tong; Lan, Ying; Zhou, Yijun; Yang, Jie

2016-05-11

Rice black-streaked dwarf virus (RBSDV) belongs to the genus Fijivirus in the family of Reoviridae and causes severe yield loss in rice-producing areas in Asia. RNA silencing, as a natural defence mechanism against plant viruses, has been successfully exploited for engineering virus resistance in plants, including rice. In this study, we generated transgenic rice lines harbouring a hairpin RNA (hpRNA) construct targeting four RBSDV genes, S1, S2, S6 and S10, encoding the RNA-dependent RNA polymerase, the putative core protein, the RNA silencing suppressor and the outer capsid protein, respectively. Both field nursery and artificial inoculation assays of three generations of the transgenic lines showed that they had strong resistance to RBSDV infection. The RBSDV resistance in the segregating transgenic populations correlated perfectly with the presence of the hpRNA transgene. Furthermore, the hpRNA transgene was expressed in the highly resistant transgenic lines, giving rise to abundant levels of 21-24 nt small interfering RNA (siRNA). By small RNA deep sequencing, the RBSDV-resistant transgenic lines detected siRNAs from all four viral gene sequences in the hpRNA transgene, indicating that the whole chimeric fusion sequence can be efficiently processed by Dicer into siRNAs. Taken together, our results suggest that long hpRNA targeting multiple viral genes can be used to generate stable and durable virus resistance in rice, as well as other plant species.

Characterization of rice black-streaked dwarf virus- and rice stripe virus-derived siRNAs in singly and doubly infected insect vector Laodelphax striatellus.

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Junmin Li

Full Text Available Replication of RNA viruses in insect cells triggers an antiviral defense that is mediated by RNA interference (RNAi which generates viral-derived small interfering RNAs (siRNAs. However, it is not known whether an antiviral RNAi response is also induced in insects by reoviruses, whose double-stranded RNA genome replication is thought to occur within core particles. Deep sequencing of small RNAs showed that when the small brown planthopper (Laodelphax striatellus was infected by Rice black-streaked dwarf virus (RBSDV (Reoviridae; Fijivirus, more viral-derived siRNAs accumulated than when the vector insect was infected by Rice stripe virus (RSV, a negative single-stranded RNA virus. RBSDV siRNAs were predominantly 21 and 22 nucleotides long and there were almost equal numbers of positive and negative sense. RBSDV siRNAs were frequently generated from hotspots in the 5'- and 3'-terminal regions of viral genome segments but these hotspots were not associated with any predicted RNA secondary structures. Under laboratory condition, L. striatellus can be infected simultaneously with RBSDV and RSV. Double infection enhanced the accumulation of particular genome segments but not viral coat protein of RBSDV and correlated with an increase in the abundance of siRNAs derived from RBSDV. The results of this study suggest that reovirus replication in its insect vector potentially induces an RNAi-mediated antiviral response.

The 3′ Untranslated Region of Tobacco Necrosis Virus RNA Contains a Barley Yellow Dwarf Virus-Like Cap-Independent Translation Element

Science.gov (United States)

Shen, Ruizhong; Miller, W. Allen

2004-01-01

RNAs of many viruses are translated efficiently in the absence of a 5′ cap structure. The tobacco necrosis virus (TNV) genome is an uncapped, nonpolyadenylated RNA whose translation mechanism has not been well investigated. Computational analysis predicted a cap-independent translation element (TE) within the 3′ untranslated region (3′ UTR) of TNV RNA that resembles the TE of barley yellow dwarf virus (BYDV), a luteovirus. Here we report that such a TE does indeed exist in the 3′ UTR of TNV strain D. Like the BYDV TE, the TNV TE (i) functions both in vitro and in vivo, (ii) requires additional sequence for cap-independent translation in vivo, (iii) has a similar secondary structure and the conserved sequence CGGAUCCUGGGAAACAGG, (iv) is inactivated by a four-base duplication in this conserved sequence, (v) can function in the 5′ UTR, and (vi) when located in its natural 3′ location, may form long-distance base pairing with the viral 5′ UTR that is conserved and probably required. The TNV TE differs from the BYDV TE by having only three helical domains instead of four. Similar structures were found in all members of the Necrovirus genus of the Tombusviridae family, except satellite tobacco necrosis virus, which harbors a different 3′ cap-independent translation domain. The presence of the BYDV-like TE in select genera of different families indicates that phylogenetic distribution of TEs does not follow standard viral taxonomic relationships. We propose a new class of cap-independent TE called BYDV-like TE. PMID:15078948

Tripartite interactions of Barley yellow dwarf virus, Sitobion avenae and wheat varieties.

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Xiao-Feng Liu

Full Text Available The tripartite interactions in a pathosystem involving wheat (Triticum aestivum L., the Barley yellow dwarf virus (BYDV, and the BYDV vector aphid Sitobion avenae were studied under field conditions to determine the impact of these interactions on aphid populations, virus pathology and grain yield. Wheat varietal resistance to BYDV and aphids varied among the three wheat varieties studied over two consecutive years. The results demonstrated that (1 aphid peak number (APN in the aphid + BYDV (viruliferous aphid treatment was greater and occurred earlier than that in the non-viruliferous aphid treatment. The APN and the area under the curve of population dynamics (AUC on a S. avenae-resistant variety 98-10-30 was significantly lower than on two aphid-susceptible varieties Tam200(13G and Xiaoyan6. (2 The production of alatae (PA was greater on the variety 98-10-30 than on the other varieties, and PA was greater in the aphid + BYDV treatment on 98-10-30 than in the non-viruliferous aphid treatment, but this trend was reversed on Tam200(13G and Xiaoyan6. (3 The BYDV disease incidence (DIC on the variety 98-10-30 was greater than that on the other two varieties in 2012, and the disease index (DID on Tam200(13G was lower than on the other varieties in the aphid + BYDV and BYDV treatments in 2012, but not in 2011 when aphid vector numbers were generally lower. (4 Yield loss in the aphid + BYDV treatment tended to be greater than that in the aphid or BYDV alone treatments across varieties and years. We suggested that aphid population development and BYDV transmission tend to promote each other under field conditions. The aphids + BYDV treatment caused greater yield reductions than non-viruliferous aphids or virus treatment. Wheat varietal resistance in 98-10-30 affects the aphid dispersal, virus transmission and wheat yield loss though inhibits aphid populations from increasing.

Tripartite Interactions of Barley Yellow Dwarf Virus, Sitobion avenae and Wheat Varieties

Science.gov (United States)

Liu, Xiao-Feng; Hu, Xiang-Shun; Keller, Mike A.; Zhao, Hui-Yan; Wu, Yun-Feng; Liu, Tong-Xian

2014-01-01

The tripartite interactions in a pathosystem involving wheat (Triticum aestivum L.), the Barley yellow dwarf virus (BYDV), and the BYDV vector aphid Sitobion avenae were studied under field conditions to determine the impact of these interactions on aphid populations, virus pathology and grain yield. Wheat varietal resistance to BYDV and aphids varied among the three wheat varieties studied over two consecutive years. The results demonstrated that (1) aphid peak number (APN) in the aphid + BYDV (viruliferous aphid) treatment was greater and occurred earlier than that in the non-viruliferous aphid treatment. The APN and the area under the curve of population dynamics (AUC) on a S. avenae-resistant variety 98-10-30 was significantly lower than on two aphid-susceptible varieties Tam200(13)G and Xiaoyan6. (2) The production of alatae (PA) was greater on the variety 98-10-30 than on the other varieties, and PA was greater in the aphid + BYDV treatment on 98-10-30 than in the non-viruliferous aphid treatment, but this trend was reversed on Tam200(13)G and Xiaoyan6. (3) The BYDV disease incidence (DIC) on the variety 98-10-30 was greater than that on the other two varieties in 2012, and the disease index (DID) on Tam200(13)G was lower than on the other varieties in the aphid + BYDV and BYDV treatments in 2012, but not in 2011 when aphid vector numbers were generally lower. (4) Yield loss in the aphid + BYDV treatment tended to be greater than that in the aphid or BYDV alone treatments across varieties and years. We suggested that aphid population development and BYDV transmission tend to promote each other under field conditions. The aphids + BYDV treatment caused greater yield reductions than non-viruliferous aphids or virus treatment. Wheat varietal resistance in 98-10-30 affects the aphid dispersal, virus transmission and wheat yield loss though inhibits aphid populations from increasing. PMID:25184214

Seed rescue from photoperiod sensitive American Joint Vetch (Aeschynomene americana L.) accessions using hydroponic cloning and aeroponics

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American joint vetch, Aeschynomene Americana L. is a self-pollinated tropical pasture legume and the USDA, ARS, PGRCU curates 137 accessions from the United States, S. America, Mexico, Central America, and Zambia. Many accessions in this collection are photoperiod sensitive due to their typical flow...

Biomass and nitrogen accumulation of hairy vetch-cereal rye cover crop mixtures as influenced by species proportions

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The performance and suitability of a legume-grass cover crop mixture for specific functions may be influenced by the proportions of each species in the mixture. The objectives of this study were to: 1) evaluate aboveground biomass and species biomass proportions at different hairy vetch (Vicia villo...

Detection, Occurrence, and Survey of Rice Stripe and Black-Streaked Dwarf Diseases in Zhejiang Province, China

OpenAIRE

Heng-mu ZHANG; Hua-di WANG; Jian YANG; Michael J ADAMS; Jian-ping CHEN

2013-01-01

The major viral diseases that occur on rice plants in Zhejiang Province, eastern China, are stripe and rice black-streaked dwarf diseases. Rice stripe disease is only caused by rice stripe tenuivirus (RSV), while rice black-streaked dwarf disease can be caused by rice black-streaked dwarf fijivirus (RBSDV) and/or southern rice black-streaked dwarf fijivirus (SRBSDV). Here we review the characterization of these viruses, methods for their detection, and extensive surveys showing their occurren...

Complete genome sequence and integrated protein localization and interaction map for alfalfa dwarf virus, which combines properties of both cytoplasmic and nuclear plant rhabdoviruses

Energy Technology Data Exchange (ETDEWEB)

Bejerman, Nicolás, E-mail: n.bejerman@uq.edu.au [Instituto de Patología Vegetal (IPAVE), Centro de Investigaciones Agropecuarias (CIAP), Instituto Nacional de Tecnología Agropecuaria INTA, Camino a 60 Cuadras k 5,5, Córdoba X5020ICA (Argentina); Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, St Lucia, QLD 4072 (Australia); Giolitti, Fabián; Breuil, Soledad de; Trucco, Verónica; Nome, Claudia; Lenardon, Sergio [Instituto de Patología Vegetal (IPAVE), Centro de Investigaciones Agropecuarias (CIAP), Instituto Nacional de Tecnología Agropecuaria INTA, Camino a 60 Cuadras k 5,5, Córdoba X5020ICA (Argentina); Dietzgen, Ralf G. [Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, St Lucia, QLD 4072 (Australia)

2015-09-15

Summary: We have determined the full-length 14,491-nucleotide genome sequence of a new plant rhabdovirus, alfalfa dwarf virus (ADV). Seven open reading frames (ORFs) were identified in the antigenomic orientation of the negative-sense, single-stranded viral RNA, in the order 3′-N-P-P3-M-G-P6-L-5′. The ORFs are separated by conserved intergenic regions and the genome coding region is flanked by complementary 3′ leader and 5′ trailer sequences. Phylogenetic analysis of the nucleoprotein amino acid sequence indicated that this alfalfa-infecting rhabdovirus is related to viruses in the genus Cytorhabdovirus. When transiently expressed as GFP fusions in Nicotiana benthamiana leaves, most ADV proteins accumulated in the cell periphery, but unexpectedly P protein was localized exclusively in the nucleus. ADV P protein was shown to have a homotypic, and heterotypic nuclear interactions with N, P3 and M proteins by bimolecular fluorescence complementation. ADV appears unique in that it combines properties of both cytoplasmic and nuclear plant rhabdoviruses. - Highlights: • The complete genome of alfalfa dwarf virus is obtained. • An integrated localization and interaction map for ADV is determined. • ADV has a genome sequence similarity and evolutionary links with cytorhabdoviruses. • ADV protein localization and interaction data show an association with the nucleus. • ADV combines properties of both cytoplasmic and nuclear plant rhabdoviruses.

Complete genome sequence and integrated protein localization and interaction map for alfalfa dwarf virus, which combines properties of both cytoplasmic and nuclear plant rhabdoviruses

International Nuclear Information System (INIS)

Bejerman, Nicolás; Giolitti, Fabián; Breuil, Soledad de; Trucco, Verónica; Nome, Claudia; Lenardon, Sergio; Dietzgen, Ralf G.

2015-01-01

Summary: We have determined the full-length 14,491-nucleotide genome sequence of a new plant rhabdovirus, alfalfa dwarf virus (ADV). Seven open reading frames (ORFs) were identified in the antigenomic orientation of the negative-sense, single-stranded viral RNA, in the order 3′-N-P-P3-M-G-P6-L-5′. The ORFs are separated by conserved intergenic regions and the genome coding region is flanked by complementary 3′ leader and 5′ trailer sequences. Phylogenetic analysis of the nucleoprotein amino acid sequence indicated that this alfalfa-infecting rhabdovirus is related to viruses in the genus Cytorhabdovirus. When transiently expressed as GFP fusions in Nicotiana benthamiana leaves, most ADV proteins accumulated in the cell periphery, but unexpectedly P protein was localized exclusively in the nucleus. ADV P protein was shown to have a homotypic, and heterotypic nuclear interactions with N, P3 and M proteins by bimolecular fluorescence complementation. ADV appears unique in that it combines properties of both cytoplasmic and nuclear plant rhabdoviruses. - Highlights: • The complete genome of alfalfa dwarf virus is obtained. • An integrated localization and interaction map for ADV is determined. • ADV has a genome sequence similarity and evolutionary links with cytorhabdoviruses. • ADV protein localization and interaction data show an association with the nucleus. • ADV combines properties of both cytoplasmic and nuclear plant rhabdoviruses

RNAi-mediated resistance to rice black-streaked dwarf virus in transgenic rice.

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Ahmed, Mohamed M S; Bian, Shiquan; Wang, Muyue; Zhao, Jing; Zhang, Bingwei; Liu, Qiaoquan; Zhang, Changquan; Tang, Shuzhu; Gu, Minghong; Yu, Hengxiu

2017-04-01

Rice black-streaked dwarf virus (RBSDV), a member of the genus Fijivirus in the family Reoviridae, causes significant economic losses in rice production in China and many other Asian countries. Development of resistant varieties by using conventional breeding methods is limited, as germplasm with high level of resistance to RBSDV have not yet been found. One of the most promising methods to confer resistance against RBSDV is the use of RNA interference (RNAi) technology. RBSDV non-structural protein P7-2, encoded by S7-2 gene, is a potential F-box protein and involved in the plant-virus interaction through the ubiquitination pathway. P8, encoded by S8 gene, is the minor core protein that possesses potent active transcriptional repression activity. In this study, we transformed rice calli using a mini-twin T-DNA vector harboring RNAi constructs of the RBSDV genes S7-2 or S8, and obtained plants harboring the target gene constructs and the selectable marker gene, hygromycin phosphotransferase (HPT). From the offspring of these transgenic plants, we obtained selectable marker (HPT gene)-free plants. Homozygous T 5 transgenic lines which harbored either S7-2-RNAi or S8-RNAi exhibited high level resistance against RBSDV under field infection pressure from indigenous viruliferous small brown planthoppers. Thus, our results showed that RNA interference with the expression of S7-2 or S8 genes seemed an effective way to induce high level resistance in rice against RBSD disease.

Profile of small interfering RNAs from cotton plants infected with the polerovirus Cotton leafroll dwarf virus

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Schrago Carlos EG

2011-08-01

Full Text Available Abstract Background In response to infection, viral genomes are processed by Dicer-like (DCL ribonuclease proteins into viral small RNAs (vsRNAs of discrete sizes. vsRNAs are then used as guides for silencing the viral genome. The profile of vsRNAs produced during the infection process has been extensively studied for some groups of viruses. However, nothing is known about the vsRNAs produced during infections of members of the economically important family Luteoviridae, a group of phloem-restricted viruses. Here, we report the characterization of a population of vsRNAs from cotton plants infected with Cotton leafroll dwarf virus (CLRDV, a member of the genus Polerovirus, family Luteoviridae. Results Deep sequencing of small RNAs (sRNAs from leaves of CLRDV-infected cotton plants revealed that the vsRNAs were 21- to 24-nucleotides (nt long and that their sequences matched the viral genome, with higher frequencies of matches in the 3- region. There were equivalent amounts of sense and antisense vsRNAs, and the 22-nt class of small RNAs was predominant. During infection, cotton Dcl transcripts appeared to be up-regulated, while Dcl2 appeared to be down-regulated. Conclusions This is the first report on the profile of sRNAs in a plant infected with a virus from the family Luteoviridae. Our sequence data strongly suggest that virus-derived double-stranded RNA functions as one of the main precursors of vsRNAs. Judging by the profiled size classes, all cotton DCLs might be working to silence the virus. The possible causes for the unexpectedly high accumulation of 22-nt vsRNAs are discussed. CLRDV is the causal agent of Cotton blue disease, which occurs worldwide. Our results are an important contribution for understanding the molecular mechanisms involved in this and related diseases.

Profile of small interfering RNAs from cotton plants infected with the polerovirus Cotton leafroll dwarf virus.

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Silva, Tatiane F; Romanel, Elisson A C; Andrade, Roberto R S; Farinelli, Laurent; Østerås, Magne; Deluen, Cécile; Corrêa, Régis L; Schrago, Carlos E G; Vaslin, Maite F S

2011-08-24

In response to infection, viral genomes are processed by Dicer-like (DCL) ribonuclease proteins into viral small RNAs (vsRNAs) of discrete sizes. vsRNAs are then used as guides for silencing the viral genome. The profile of vsRNAs produced during the infection process has been extensively studied for some groups of viruses. However, nothing is known about the vsRNAs produced during infections of members of the economically important family Luteoviridae, a group of phloem-restricted viruses. Here, we report the characterization of a population of vsRNAs from cotton plants infected with Cotton leafroll dwarf virus (CLRDV), a member of the genus Polerovirus, family Luteoviridae. Deep sequencing of small RNAs (sRNAs) from leaves of CLRDV-infected cotton plants revealed that the vsRNAs were 21- to 24-nucleotides (nt) long and that their sequences matched the viral genome, with higher frequencies of matches in the 3- region. There were equivalent amounts of sense and antisense vsRNAs, and the 22-nt class of small RNAs was predominant. During infection, cotton Dcl transcripts appeared to be up-regulated, while Dcl2 appeared to be down-regulated. This is the first report on the profile of sRNAs in a plant infected with a virus from the family Luteoviridae. Our sequence data strongly suggest that virus-derived double-stranded RNA functions as one of the main precursors of vsRNAs. Judging by the profiled size classes, all cotton DCLs might be working to silence the virus. The possible causes for the unexpectedly high accumulation of 22-nt vsRNAs are discussed. CLRDV is the causal agent of Cotton blue disease, which occurs worldwide. Our results are an important contribution for understanding the molecular mechanisms involved in this and related diseases.

White dwarf-red dwarf binaries in the Galaxy

NARCIS (Netherlands)

Besselaar, E.J.M. van den

2007-01-01

This PhD thesis shows several studies on white dwarf - red dwarf binaries. White dwarfs are the end products of most stars and red dwarfs are normal hydrogen burning low-mass stars. White dwarf - red dwarf binaries are both blue (white dwarf) and red (red dwarf). Together with the fact that they are

Weed Control Efficiency of wild Safflower (Carthamus oxyacanthus M. Bieb in Replacement Series Technique of Barley (Hordeum vulgare L. and Common Vetch (Vicia sativa L.

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abdolreza ahmadi

2017-08-01

Full Text Available Introduction In agronomy, natural outlook has been expressed in different forms which stable agriculture is an example. Stable agriculture is ascribed to the authentic management of agricultural resources, which in addition to fulfilling the ever-changing needs of humans, maintains the health of environment and capacity of water and soil resources. Application of herbicides, besides being costly, resulted in the selection of herbicide resistant weed species and has become an environmental contamination factor. However, reduction of herbicide consumption is one of the goals of modern agriculture, with several methods being suggested, including intercropping. In natural conditions of production, environment conservation of weed existence requires cost. One of the important preparations in weed control from the perspective of sustainable agriculture, is using intercropping system. The aim of this study was to determine the role of crop diversity on weed and crop production based on the beneficial effects of intercropping system than pure. Materials and methods In order to study effects of mixed and sole cropping of barley with common vetch on their biologic yield and utilization indices, an experiment was conducted in Agricultural college of the University of Lorestan, during the growing season of 2013-2014 with 24 treatments using the method of rows replacement series technique by the randomized complete block design in a factorial arrangement with three replications. First factor included 6 levels of intercropping: sole cropping of common vetch (100%, 55-45 (Common vetch-barley, 35-65, 45-55, 65-35 and sole cropping of barley and second factor included 4 levels of weed wild safflower, control, 10, 15 and 20 plants per m2. In this experiment WCE, LER and CR were measured. The data were subjected to analysis of variance (ANOVA using Mstat-C computer software. Mean comparisons were performed using Duncan’s multiple range test at two levels of

Nitrogen cycling in an ecological farming system of milk vetch culture - pig raising - biogas fermentation - rice culture

NARCIS (Netherlands)

Liu, J.R.; Berge, ten H.F.M.; Zhang, M.L.; Wu, J.F.; Guo, C.Z.; Liu, W.

2002-01-01

The [15]N - labeled technique was used to study the stock, transformation, fate and utilization efficiency of N in the farming-pig husbandry-biogas ecosystem in rice areas. It was shown that the crude protein digestibility of the ensilaged milk vetch by pig was 53.76%, the recovery rates of

Researches on Determination Yield and Yield Components of Some Common Vetch (Vicia sativa L. Genotypes in Ecological Conditions of Diyarbakır

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Seyithan SEYDOŞOĞLU

2014-09-01

Full Text Available The research was conducted to determine yield and yield components of some common vetch genotypes in order to examine some of the traits, during 2011-2013 seasons in GAP International Agricultural Research and Training Center was carried out on the experimental field. In the study, a total of 20 different genotypes were used common vetch, field trials randomized block design with 3 replications was established. In the study, herbage yield, hay yield and seed yield in addition to days to %50 flowering duration, plant height, main stem length, main stem number, pod number per plant, grain number per pod as affecting yield some properties were also investigated. In both years of the study, days to %50 flowering duration and grain number per pod characteristics examined, except among genotypes for all other parameters are determined significant differences in statistical terms. According to the average of two years result; days to %50 flowering duration, plant height, main stem length, main stem number, pod number per plant, grain number per pod, herbage yield, hay yield, seed yield, 1000 seed weight were changed between 157.8-174.0 days, 33.9-62.6 cm, 52.0-83.3 cm, 1.6-2.6 number, 13.5-21.2 number, 4.7-5.6 number, 1522.0-3232.3 kg da-1, 308.0-919.5 kg da-1, 92.2-293.7 kg da-1, 46.5-84.5 g, respectively. According to these results, under the climate and soil conditions of Diyarbakır; for the grass production common vetch genotypes "D-135" was suggested and for the seed production common vetch genotypes "IFVS-715" and "GAP-59998" were suggested.

The P0 protein encoded by cotton leafroll dwarf virus (CLRDV) inhibits local but not systemic RNA silencing.

Science.gov (United States)

Delfosse, Verónica C; Agrofoglio, Yamila C; Casse, María F; Kresic, Iván Bonacic; Hopp, H Esteban; Ziegler-Graff, Véronique; Distéfano, Ana J

2014-02-13

Plants employ RNA silencing as a natural defense mechanism against viruses. As a counter-defense, viruses encode silencing suppressor proteins (SSPs) that suppress RNA silencing. Most, but not all, the P0 proteins encoded by poleroviruses have been identified as SSP. In this study, we demonstrated that cotton leafroll dwarf virus (CLRDV, genus Polerovirus) P0 protein suppressed local silencing that was induced by sense or inverted repeat transgenes in Agrobacterium co-infiltration assay in Nicotiana benthamiana plants. A CLRDV full-length infectious cDNA clone that is able to infect N. benthamiana through Agrobacterium-mediated inoculation also inhibited local silencing in co-infiltration assays, suggesting that the P0 protein exhibits similar RNA silencing suppression activity when expressed from the full-length viral genome. On the other hand, the P0 protein did not efficiently inhibit the spread of systemic silencing signals. Moreover, Northern blotting indicated that the P0 protein inhibits the generation of secondary but not primary small interfering RNAs. The study of CLRDV P0 suppression activity may contribute to understanding the molecular mechanisms involved in the induction of cotton blue disease by CLRDV infection. Copyright © 2013 Elsevier B.V. All rights reserved.

Barley yellow dwarf virus in barley crops in Tunisia: prevalence and molecular characterization

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Asma NAJAR

2017-05-01

Full Text Available A field survey was conducted in Tunisia in the North-Eastern regions (Bizerte, CapBon and Zaghouan, the North-Western region (Kef and the Central-Eastern region (Kairouan during the 2011/2012 growing season, in order to determine the incidence and the geographic distribution of Barley yellow dwarf virus (BYDVs in barley fields. Tissue blot immunoassays (TBIA showed that BYDV was most common in Zaghouan (incidence 14%, Cap Bon (14% and Bizerte (35%, in randomly collected samples from these three locations.Among the different BYDVs identified, BYDV-PAV (64% was the most common followed by BYDV-MAV (16% and CYDV-RPV (3%. The coat protein gene sequences of six isolates collected from different regions shared >98% pairwise similarity. In comparisons with other BYDV sequences from around the world, the Tunisian sequences shared greatest homology with isolates 109 and ASL1 from the United States of America and Germany (≈97%, and <90% with all other isolate sequences available in public databases.

Evaluation of Rice Resistance to Southern Rice Black-Streaked Dwarf Virus and Rice Ragged Stunt Virus through Combined Field Tests, Quantitative Real-Time PCR, and Proteome Analysis.

Science.gov (United States)

Wang, Zhenchao; Yu, Lu; Jin, Linhong; Wang, Wenli; Zhao, Qi; Ran, Longlu; Li, Xiangyang; Chen, Zhuo; Guo, Rong; Wei, Yongtian; Yang, Zhongcheng; Liu, Enlong; Hu, Deyu; Song, Baoan

2017-02-22

Diseases caused by southern rice black-streaked dwarf virus (SRBSDV) and rice ragged stunt virus (RRSV) considerably decrease grain yield. Therefore, determining rice cultivars with high resistance to SRBSDV and RRSV is necessary. In this study, rice cultivars with high resistance to SRBSDV and RRSV were evaluated through field trials in Shidian and Mangshi county, Yunnan province, China. SYBR Green I-based quantitative real-time polymerase chain reaction (qRT-PCR) analysis was used to quantitatively detect virus gene expression levels in different rice varieties. The following parameters were applied to evaluate rice resistance: acre yield (A.Y.), incidence of infected plants (I.I.P.), virus load (V.L.), disease index (D.I.), and insect quantity (I.Q.) per 100 clusters. Zhongzheyou1 (Z1) and Liangyou2186 (L2186) were considered the most suitable varieties with integrated higher A.Y., lower I.I.P., V.L., D.I. and I.Q. In order to investigate the mechanism of rice resistance, comparative label-free shotgun liquid chromatography tandem-mass spectrometry (LC-MS/MS) proteomic approaches were applied to comprehensively describe the proteomics of rice varieties' SRBSDV tolerance. Systemic acquired resistance (SAR)-related proteins in Z1 and L2186 may result in the superior resistance of these varieties compared with Fengyouxiangzhan (FYXZ).

Virus incidence in orchardgrass (Dactylis glomerata L.) seed production fields in the Willamette Valley

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A survey was conducted over the course of three years (2014-2016) for the presence of Barley yellow dwarf virus (BYDV-MAV and BYDV-PAV), Cereal yellow dwarf virus (CYDV-RPV), and Cocksfoot mottle virus (CfMV) in orchardgrass (Dactylis glomerata) fields in the Willamette Valley, Oregon. There was an ...

The complete nucleotide sequence of the barley yellow dwarf GPV isolate from China shows that it is a new member of the genus Polerovirus.

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Zhang, Wenwei; Cheng, Zhuomin; Xu, Lei; Wu, Maosen; Waterhouse, Peter; Zhou, Guanghe; Li, Shifang

2009-01-01

The complete nucleotide sequence of the ssRNA genome of a Chinese GPV isolate of barley yellow dwarf virus (BYDV) was determined. It comprised 5673 nucleotides, and the deduced genome organization resembled that of members of the genus Polerovirus. It was most closely related to cereal yellow dwarf virus-RPV (77% nt identity over the entire genome; coat protein amino acid identity 79%). The GPV isolate also differs in vector specificity from other BYDV strains. Biological properties, phylogenetic analyses and detailed sequence comparisons suggest that GPV should be considered a member of a new species within the genus, and the name Wheat yellow dwarf virus-GPV is proposed.

A novel method for transmitting southern rice black-streaked dwarf virus to rice without insect vector.

Science.gov (United States)

Yu, Lu; Shi, Jing; Cao, Lianlian; Zhang, Guoping; Wang, Wenli; Hu, Deyu; Song, Baoan

2017-08-15

Southern rice black-streaked dwarf virus (SRBSDV) has spread from the south of China to the north of Vietnam in the past few years, and has severely influenced rice production. However, previous study of traditional SRBSDV transmission method by the natural virus vector, the white-backed planthopper (WBPH, Sogatella furcifera), in the laboratory, researchers are frequently confronted with lack of enough viral samples due to the limited life span of infected vectors and rice plants and low virus acquisition and inoculation efficiency by the vector. Meanwhile, traditional mechanical inoculation of virus only apply to dicotyledon because of the higher content of lignin in the leaves of the monocot. Therefore, establishing an efficient and persistent-transmitting model, with a shorter virus transmission time and a higher virus transmission efficiency, for screening novel anti-SRBSDV drugs is an urgent need. In this study, we firstly reported a novel method for transmitting SRBSDV in rice using the bud-cutting method. The transmission efficiency of SRBSDV in rice was investigated via the polymerase chain reaction (PCR) method and the replication of SRBSDV in rice was also investigated via the proteomics analysis. Rice infected with SRBSDV using the bud-cutting method exhibited similar symptoms to those infected by the WBPH, and the transmission efficiency (>80.00%), which was determined using the PCR method, and the virus transmission time (30 min) were superior to those achieved that transmitted by the WBPH. Proteomics analysis confirmed that SRBSDV P1, P2, P3, P4, P5-1, P5-2, P6, P8, P9-1, P9-2, and P10 proteins were present in infected rice seedlings infected via the bud-cutting method. The results showed that SRBSDV could be successfully transmitted via the bud-cutting method and plants infected SRBSDV exhibited the symptoms were similar to those transmitted by the WBPH. Therefore, the use of the bud-cutting method to generate a cheap, efficient, reliable supply of

Mapping the nuclear localization signal in the matrix protein of potato yellow dwarf virus.

Science.gov (United States)

Anderson, Gavin; Jang, Chanyong; Wang, Renyuan; Goodin, Michael

2018-05-01

The ability of the matrix (M) protein of potato yellow dwarf virus (PYDV) to remodel nuclear membranes is controlled by a di-leucine motif located at residues 223 and 224 of its primary structure. This function can be uncoupled from that of its nuclear localization signal (NLS), which is controlled primarily by lysine and arginine residues immediately downstream of the LL motif. In planta localization of green fluorescent protein fusions, bimolecular fluorescence complementation assays with nuclear import receptor importin-α1 and yeast-based nuclear import assays provided three independent experimental approaches to validate the authenticity of the M-NLS. The carboxy terminus of M is predicted to contain a nuclear export signal, which is belived to be functional, given the ability of M to bind the Arabidopsis nuclear export receptor 1 (XPO1). The nuclear shuttle activity of M has implications for the cell-to-cell movement of PYDV nucleocapsids, based upon its interaction with the N and Y proteins.

Biosynthesis of raffinose family oligosaccharides and galactosyl pinitols in developing and maturing seeds of winter vetch (Vicia vlllosa Roth.

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Lesław B. Lahuta

2011-01-01

Full Text Available Changes in the accumulation of two types of α-D-galactosides: raffinose family oligosaccharides and galactosyl pinitols were compared with changes in the activities of galactosyltransferases during winter vetch (Vicia villosa Roth. seed development and maturation. Occurrence of galactinol and raffinose in young seeds and changes in activities of galactinol synthase and raffinose synthase during seed development indicated that formation of raffinose oligosaccharides (RFOs preceded synthesis of galactopinitols. Although transfer of galactose residues into raffinose oligosaccharides increased as seeds were maturing, at late stages of seed maturation the accumulation of galactopinitols was preferred to that of RFOs. In the present study, activities of enzymes transferring galactose moieties from galactinol to D-pinitol forming galactopinitol A, and further transfer of galactose moieties from galactinol to mono- and di-galactopinitol A were detected throughout seed development and maturation. This is a new observation, indicating biological potential of winter vetch seeds to synthesize mono-, di- and tri-galactosides of D-pinitol in a pathway similar to RFOs. The pattern of changes in activities of stachyose synthase and enzymes synthesizing galactopinitols (named galactopinitol A synthase and ciceritol synthase suggests that formation of stachyose, mono- and di-galactopinitol A (ciceritol is catalyzed by one enzyme. High correlation between activities of verbascose synthase and enzyme catalyzing synthesis of tri-galactopinitol A from galactinol and ciceritol (named tri-galactopinitol A synthase also suggests that biosynthesis of both types of tri-galactosides was catalyzed by one enzyme, but distinct from stachyose synthase. Changes in concentrations of galactosyl acceptors (sucrose and D-pinitol can be a factor which regulates splitting of galactose moieties between both types of galactosides in winter vetch seeds.

Incidence of viruses in fescue (Festuca sp.) seed production fields in the Willamette Valley in 2016

Science.gov (United States)

Tall Fescue seed production fields of Western Oregon were sampled and tested for the presence or absence of three viruses, Barley yellow dwarf virus (BYDV) -MAV and -PAV, and Cereal yellow dwarf virus (CYDV). There was no BYDV-MAV detected in any of the Fescue seed fields. The BYDV-PAV occurred in ...

Genetic variation of eggplant mottled dwarf virus from annual and perennial plant hosts.

Science.gov (United States)

Pappi, Polyxeni G; Maliogka, Varvara I; Amoutzias, Gregory D; Katis, Nikolaos I

2016-03-01

The genetic diversity of eggplant mottled dwarf virus (EMDV), a member of the family Rhabdoviridae, was studied using isolates collected from different herbaceous and woody plant species and remote geographic areas. Sequences corresponding to the N, X, P, Y, M and G ORFs as well as the untranslated regions (UTRs) between ORFs were determined from all isolates. Low genetic diversity was found in almost all genomic regions studied except for the X ORF and the UTRs, which were more variable, while interestingly, an EMDV isolate from caper possessed a truncated G gene sequence. Furthermore, low d N /d S ratios, indicative of purifying selection, were calculated for all genes. Phylogenetic analysis showed that the EMDV isolates clustered in three distinct subgroups based on their geographical origin, with the exception of one subgroup that consisted of isolates from northern Greece and Cyprus. Overall, the level of genetic diversity of EMDV differed between seed- and asexually propagated plants in our collection, and this could be related to the mode of transmission.

Selective constraints, molecular recombination structure and phylogenetic reconstruction of isometric plant RNA viruses of the families Luteoviridae and Tymoviridae.

Science.gov (United States)

Boulila, Moncef

2011-02-01

In an effort to enhance the knowledge on molecular evolution of currently the known members of the families Luteoviridae and Tymoviridae, in-depth molecular investigations in the entire genome of 147 accessions retrieved from the international databases, were carried out. Two algorithms (RECCO and RDP version 3.31β) adapted to the mosaic structure of viruses were utilized. The recombination frequency along the sequences was dissected and demonstrated that the three virus genera of the family Luteoviridae comprise numerous members subjected to recombination. It has pointed out that the major viruses swapped a few but long genomic segments. In addition, in Barley yellow dwarf virus, heredity material might be exchanged between two different serotypes. Even more, putative recombination events occurred between two different genera. Based on Fisher's Exact Test of Neutrality, positive selection acting on protein expression was detected only in the poleroviruses Cereal yellow dwarf virus, Potato leafroll virus and Wheat yellow dwarf virus. In contrast, several components of the family Tymoviridae were highly recombinant. Genomic portion exchange arose in many positions consisting of short fragments. Furthermore, no positive selection was detected. The evolutionary history showed, in the Luteoviridae, that all screened isolates split into three clusters corresponding to the three virus genera forming this family. Moreover, in the serotype PAV of Barley yellow dwarf virus, two major clades corresponding to PAV-USA and PAV-China, were delineated. Similarly, in the Tymoviridae, all analyzed isolates fell into four groups corresponding to the three virus genera composing this family along with the unclassified Tymoviridae. Inferred phylogenies reshuffled the existing classification and showed that Wheat yellow dwarf virus-RPV was genetically closely related to Cereal yellow dwarf virus and the unclassified Tymoviridae Grapevine syrah virus-1 constituted an integral part of

Identification of virus isolates inducing mosaic of sugarcane in ...

African Journals Online (AJOL)

Sugarcane mosaic disease caused by sugarcane mosaic virus (SCMV), Johnsongrass mosaic virus (JGMV), maize dwarf mosaic virus (MDMV) and sorghum mosaic Virus (SrMV) is an economically important viral disease of sugarcane worldwide. Field survey was conducted to assess the presence of the viruses involve in ...

Star Formation in Dwarf-Dwarf Mergers: Fueling Hierarchical Assembly

Science.gov (United States)

Stierwalt, Sabrina; Johnson, K. E.; Kallivayalil, N.; Patton, D. R.; Putman, M. E.; Besla, G.; Geha, M. C.

2014-01-01

We present early results from the first systematic study a sample of isolated interacting dwarf pairs and the mechanisms governing their star formation. Low mass dwarf galaxies are ubiquitous in the local universe, yet the efficiency of gas removal and the enhancement of star formation in dwarfs via pre-processing (i.e. dwarf-dwarf interactions occurring before the accretion by a massive host) are currently unconstrained. Studies of Local Group dwarfs credit stochastic internal processes for their complicated star formation histories, but a few intriguing examples suggest interactions among dwarfs may produce enhanced star formation. We combine archival UV imaging from GALEX with deep optical broad- and narrow-band (Halpha) imaging taken with the pre- One Degree Imager (pODI) on the WIYN 3.5-m telescope and with the 2.3-m Bok telescope at Steward Observatory to confirm the presence of stellar bridges and tidal tails and to determine whether dwarf-dwarf interactions alone can trigger significant levels of star formation. We investigate star formation rates and global galaxy colors as a function of dwarf pair separation (i.e. the dwarf merger sequence) and dwarf-dwarf mass ratio. This project is a precursor to an ongoing effort to obtain high spatial resolution HI imaging to assess the importance of sequential triggering caused by dwarf-dwarf interactions and the subsequent affect on the more massive hosts that later accrete the low mass systems.

Allelopathy in the natural and agricultural ecosystems and isolation of potent allelochemicals from Velvet bean (Mucuna pruriens) and Hairy vetch (Vicia villosa).

Science.gov (United States)

Fujii, Yoshiharu

2003-06-01

We have studied on allelopathy of plants and developed methods to identify the effective substances in root exudates, leaf leacheate, and volatile chemicals emitted from plants. We found traditional cover plants that show allelopathic activity are useful for weed control. It could eliminate the use of synthetic chemicals for this purpose. Allelopathy is a natural power of plants to protect themselves by producing natural organic chemicals. Some endemic plants in Asia, already known by farmers in the region, as either cover crops used in intercropping, hedgerow, or agroforestry, were found to possess strong allelopathic abilities. Our group identified several allelochemicals from these plants. These allelopathic cover crops, mostly leguminous plants, provide protein rich food, and grow easily without artificial fertilizers, herbicides, insecticides and fungicides. In this regards, these allelopathic cover crops could save food shortage in rural area, and are useful for environmental conservation. Screenings of allelopathic plants by specific bioassays and field tests have been conducted. Hairy vetch (Vicia villosa) and Velvet bean (Mucuna pruriens) are two promising species for the practical application of allelopathy. An amino acid, L-DOPA, unusual in plants, plays an important role as allelochemical in Velvet bean (Mucuna pruriens). Hairy vetch is the most promising cover plant for the weed control in orchard, vegetable and rice production and even for landscape amendment in abandoned field in Japan. We have isolated "cyanamide", a well known nitrogen fertilizer, from Hairy vetch. This is the first finding of naturally produced cyanamide in the world.

Chemical composition and some anti-nutrient content of raw and processed bitter vetch (Vicia ervilia) seed for use as feeding stuff in poultry diet.

Science.gov (United States)

Sadeghi, Gh; Pourreza, J; Samei, A; Rahmani, H

2009-01-01

An experiment was conducted to determine chemical composition of raw and treated bitter vetch seed for use in poultry diets. Processing methods were: soaked in water for 12 h, then autoclaved and dried (SA); coarsely ground, soaked in water for 24 h, autoclaved and dried (GSA); coarsely ground, soaked in water for 47 h with exchange of water every 12 h, cooked and dried (GSC); coarsely ground, soaked in solution of 1% acetic acid for 24 h at 60 degrees C and dried (GAA). Raw bitter vetch seed was contained 94.52, 26.56, 0.4, 58.86, 3.38, 5.32, 12.28 and 14.20 percent DM, CP, EE, NFE, Ash, CF, ADF and NDF, respectively. Its GE, AME, AMEn, TME and TMEn values were 18.10, 13.15, 14.38, 14.10 and 14.69 MJ/kg, respectively. Results indicated that bitter vetch is a good source of Fe (340 ppm) and Cu (46.7 ppm). It s amino acid profile was suitable and methionine was the first limiting amino acid when compared with broiler and layer chicks requirements. Its canavanine and tannin content were 0.78 and 6.7 mg/kgDM, respectively. Processing methods improved CP and in some cases AMEn. All processing methods especially GSC resulted in a significant (P < 0.05) reduction in canavanine and tannin.

Infrared Colors of Dwarf-Dwarf Galaxy Interactions

Science.gov (United States)

Liss, Sandra; Stierwalt, Sabrina; Johnson, Kelsey; Patton, Dave; Kallivayalil, Nitya

2015-10-01

We request Spitzer Warm Mission IRAC Channel 1 & 2 imaging for a sample of 60 isolated dwarf galaxy pairs as a key component of a larger, multi-wavelength effort to understand the role low-mass mergers play in galaxy evolution. A systematic study of dwarf-dwarf mergers has never been done, and we wish to characterize the impact such interactions have on fueling star formation in the nearby universe. The Spitzer imaging proposed here will allow us to determine the extent to which the 3.6 and 4.5 mum bands are dominated by stellar light and investigate a) the extent to which interacting pairs show IR excess and b) whether the excess is related to the pair separation. Second, we will use this IR photometry to constrain the processes contributing to the observed color excess and scatter in each system. We will take advantage of the wealth of observations available in the Spitzer Heritage Archive for 'normal' non-interacting dwarfs by comparing the stellar populations of those dwarfs with the likely interacting dwarfs in our sample. Ultimately, we can combine the Spitzer imaging proposed here with our current, ongoing efforts to obtain groundbased optical photometry to model the star formation histories of these dwarfs and to help constrain the timescales and impact dwarf-dwarf mergers have on fueling star formation. The sensitivity and resolution offered by Spitzer are necessary to determine the dust properties of these interacting systems, and how these properties vary as a function of pair separation, mass ratio, and gas fraction.

Satellite dwarf galaxies in a hierarchical universe: the prevalence of dwarf-dwarf major mergers

International Nuclear Information System (INIS)

Deason, Alis; Wetzel, Andrew; Garrison-Kimmel, Shea

2014-01-01

Mergers are a common phenomenon in hierarchical structure formation, especially for massive galaxies and clusters, but their importance for dwarf galaxies in the Local Group remains poorly understood. We investigate the frequency of major mergers between dwarf galaxies in the Local Group using the ELVIS suite of cosmological zoom-in dissipationless simulations of Milky Way- and M31-like host halos. We find that ∼10% of satellite dwarf galaxies with M star > 10 6 M ☉ that are within the host virial radius experienced a major merger of stellar mass ratio closer than 0.1 since z = 1, with a lower fraction for lower mass dwarf galaxies. Recent merger remnants are biased toward larger radial distance and more recent virial infall times, because most recent mergers occurred shortly before crossing within the virial radius of the host halo. Satellite-satellite mergers also occur within the host halo after virial infall, catalyzed by the large fraction of dwarf galaxies that fell in as part of a group. The merger fraction doubles for dwarf galaxies outside of the host virial radius, so the most distant dwarf galaxies in the Local Group are the most likely to have experienced a recent major merger. We discuss the implications of these results on observable dwarf merger remnants, their star formation histories, the gas content of mergers, and massive black holes in dwarf galaxies.

Satellite dwarf galaxies in a hierarchical universe: the prevalence of dwarf-dwarf major mergers

Energy Technology Data Exchange (ETDEWEB)

Deason, Alis [Department of Astronomy and Astrophysics, University of California Santa Cruz, Santa Cruz, CA (United States); Wetzel, Andrew [TAPIR, California Institute of Technology, Pasadena, CA (United States); Garrison-Kimmel, Shea, E-mail: alis@ucolick.org [Center for Cosmology, Department of Physics and Astronomy, University of California, Irvine, CA (United States)

2014-10-20

Mergers are a common phenomenon in hierarchical structure formation, especially for massive galaxies and clusters, but their importance for dwarf galaxies in the Local Group remains poorly understood. We investigate the frequency of major mergers between dwarf galaxies in the Local Group using the ELVIS suite of cosmological zoom-in dissipationless simulations of Milky Way- and M31-like host halos. We find that ∼10% of satellite dwarf galaxies with M {sub star} > 10{sup 6} M {sub ☉} that are within the host virial radius experienced a major merger of stellar mass ratio closer than 0.1 since z = 1, with a lower fraction for lower mass dwarf galaxies. Recent merger remnants are biased toward larger radial distance and more recent virial infall times, because most recent mergers occurred shortly before crossing within the virial radius of the host halo. Satellite-satellite mergers also occur within the host halo after virial infall, catalyzed by the large fraction of dwarf galaxies that fell in as part of a group. The merger fraction doubles for dwarf galaxies outside of the host virial radius, so the most distant dwarf galaxies in the Local Group are the most likely to have experienced a recent major merger. We discuss the implications of these results on observable dwarf merger remnants, their star formation histories, the gas content of mergers, and massive black holes in dwarf galaxies.

THE FORNAX DWARF GALAXY AS A REMNANT OF RECENT DWARF-DWARF MERGING IN THE LOCAL GROUP

International Nuclear Information System (INIS)

Yozin, C.; Bekki, K.

2012-01-01

We present results from the first numerical analysis to support the hypothesis, first proposed in Coleman et al., that the Fornax dwarf galaxy was formed from the minor merging of two dwarfs about 2 Gyr ago. Using orbits for the Fornax dwarf that are consistent with the latest proper motion measurements, our dynamical evolution models show that the observed asymmetric shell-like substructures can be formed from the remnant of a smaller dwarf during minor merging. These models also predict the formation of diffuse stellar streams. We discuss how these stellar substructures depend on model parameters of dwarf-dwarf merging, and how the intermediate-age subpopulations found in the vicinity of these substructures may be formed from gas accretion in past merger events. We also suggest that one of Fornax's globular clusters originates from a merged dwarf companion, and demonstrate where as yet undetected tidal streams or H I gas formed from the dwarf merging may be found in the outer halo of the Galaxy.

Virus Diseases Infecting Almond Germplasm in Lebanon

OpenAIRE

Adeeb Saad; Yusuf Abou-Jawdah; Zahi Kanaan-Atallah

2000-01-01

Cultivated and wild almond species were surveyed for virus diseases. Four viruses infected cultivated almonds (Prunus dulcis): Prunus necrotic ringspot virus (PNRSV), Prune dwarf virus (PDV), Apple chlorotic leaf spot virus (ACLSV) and Apple mosaic virus (ApMV). Only ACLSV and ApMV were detected on wild almonds, (Prunus orientalis and P. korschinskii). The occurence of PNRSV or PDV on seeds used for the production of rootstocks, on seedlings in nurseries, and on mother plants reve...

Jasmonic acid-mediated defense suppresses brassinosteroid-mediated susceptibility to Rice black streaked dwarf virus infection in rice.

Science.gov (United States)

He, Yuqing; Zhang, Hehong; Sun, Zongtao; Li, Junmin; Hong, Gaojie; Zhu, Qisong; Zhou, Xuebiao; MacFarlane, Stuart; Yan, Fei; Chen, Jianping

2017-04-01

Plant hormones play a vital role in plant immune responses. However, in contrast to the relative wealth of information on hormone-mediated immunity in dicot plants, little information is available on monocot-virus defense systems. We used a high-throughput-sequencing approach to compare the global gene expression of Rice black-streaked dwarf virus (RBSDV)-infected rice plants with that of healthy plants. Exogenous hormone applications and transgenic rice were used to test RBSDV infectivity and pathogenicity. Our results revealed that the jasmonic acid (JA) pathway was induced while the brassinosteroid (BR) pathway was suppressed in infected plants. Foliar application of methyl jasmonate (MeJA) or brassinazole (BRZ) resulted in a significant reduction in RBSDV incidence, while epibrassinolide (BL) treatment increased RBSDV infection. Infection studies using coi1-13 and Go mutants demonstrated JA-mediated resistance and BR-mediated susceptibility to RBSDV infection. A mixture of MeJA and BL treatment resulted in a significant reduction in RBSDV infection compared with a single BL treatment. MeJA application efficiently suppressed the expression of BR pathway genes, and this inhibition depended on the JA coreceptor OsCOI1. Collectively, our results reveal that JA-mediated defense can suppress the BR-mediated susceptibility to RBSDV infection. © 2016 The Authors. New Phytologist © 2016 New Phytologist Trust.

Ecological Fitness of Non-vector Planthopper Sogatella furcifera on Rice Plants Infected with Rice Black Streaked Dwarf Virus

Directory of Open Access Journals (Sweden)

Xiao-chan HE

2012-12-01

Full Text Available We evaluated the effects of rice black streak dwarf virus (RBSDV-infested rice plants on the ecological parameters and its relevant defensive and detoxification enzymes of white-backed planthopper (WBPH in laboratory for exploring the relationship between RBSDV and the non-vector planthopper. The results showed that nymph survival rate, female adult weight and fecundity, and egg hatchability of WBPH fed on RBSDV-infested rice plants did not markedly differ from those on healthy plants, whereas the female adult longevity and egg duration significantly shortened on diseased plants. Furthermore, significantly higher activities of defensive enzymes (dismutase, catalase and peroxidase and detoxification enzymes (acetylcholinesterase, carboxylesterase and glutathione S-transferase were found in WBPH adults fed on infected plants. Results implied that infestation by RBSDV increased the ecological fitness of non-vector planthopper population.

Molecular Genetic Analysis and Evolution of Segment 7 in Rice Black-Streaked Dwarf Virus in China.

Directory of Open Access Journals (Sweden)

Yu Zhou

Full Text Available Rice black-streaked dwarf virus (RBSDV causes maize rough dwarf disease or rice black-streaked dwarf disease and can lead to severe yield losses in maize and rice. To analyse RBSDV evolution, codon usage bias and genetic structure were investigated in 111 maize and rice RBSDV isolates from eight geographic locations in 2013 and 2014. The linear dsRNA S7 is A+U rich, with overall codon usage biased toward codons ending with A (A3s, S7-1: 32.64%, S7-2: 29.95% or U (U3s, S7-1: 44.18%, S7-2: 46.06%. Effective number of codons (Nc values of 45.63 in S7-1 (the first open reading frame of S7 and 39.96 in S7-2 (the second open reading frame of S7 indicate low degrees of RBSDV-S7 codon usage bias, likely driven by mutational bias regardless of year, host, or geographical origin. Twelve optimal codons were detected in S7. The nucleotide diversity (π of S7 sequences in 2013 isolates (0.0307 was significantly higher than in 2014 isolates (0.0244, P = 0.0226. The nucleotide diversity (π of S7 sequences in isolates from Jinan (0.0391 was higher than that from the other seven locations (P < 0.01. Only one S7 recombinant was detected in Baoding. RBSDV isolates could be phylogenetically classified into two groups according to S7 sequences, and further classified into two subgroups. S7-1 and S7-2 were under negative and purifying selection, with respective Ka/Ks ratios of 0.0179 and 0.0537. These RBSDV populations were expanding (P < 0.01 as indicated by negative values for Tajima's D, Fu and Li's D, and Fu and Li's F. Genetic differentiation was detected in six RBSDV subpopulations (P < 0.05. Absolute Fst (0.0790 and Nm (65.12 between 2013 and 2014, absolute Fst (0.1720 and Nm (38.49 between maize and rice, and absolute Fst values of 0.0085-0.3069 and Nm values of 0.56-29.61 among these eight geographic locations revealed frequent gene flow between subpopulations. Gene flow between 2013 and 2014 was the most frequent.

Bean Yellow Dwarf Virus replicons for high-level transgene expression in transgenic plants and cell cultures.

Science.gov (United States)

Zhang, Xiuren; Mason, Hugh

2006-02-05

A novel stable transgenic plant expression system was developed using elements of the replication machinery of Bean Yellow Dwarf Virus (BeYDV). The system contains two transgenes: 1) The BeYDV replicon vector with an expression cassette flanked by cis-acting DNA elements of BeYDV, and 2) The viral replication initiator protein (Rep) controlled by an alcohol-inducible promoter. When Rep expression was triggered by treatment with ethanol, it induced release of the BeYDV replicon from stably integrated T-DNA and episomal replication to high copy number. Replicon amplification resulted in substantially increased transgene mRNA levels (up to 80-fold) and translation products (up to 10-fold) after induction of Rep expression by ethanol treatment in tobacco NT1 cells and leaves of whole potato plants. Thus, the BeYDV stable transformant replicon system is a powerful tool for plant-based production of recombinant proteins. (c) 2005 Wiley Periodicals, Inc.

The stress granule component G3BP is a novel interaction partner for the nuclear shuttle proteins of the nanovirus pea necrotic yellow dwarf virus and geminivirus abutilon mosaic virus.

Science.gov (United States)

Krapp, Susanna; Greiner, Eva; Amin, Bushra; Sonnewald, Uwe; Krenz, Björn

2017-01-02

Stress granules (SGs) are structures within cells that regulate gene expression during stress response, e.g. viral infection. In mammalian cells assembly of SGs is dependent on the Ras-GAP SH3-domain-binding protein (G3BP). The C-terminal domain of the viral nonstructural protein 3 (nsP3) of Semliki Forest virus (SFV) forms a complex with mammalian G3BP and sequesters it into viral RNA replication complexes in a manner that inhibits the formation of SGs. The binding domain of nsP3 to HsG3BP was mapped to two tandem 'FGDF' repeat motifs close to the C-terminus of the viral proteins. It was speculated that plant viruses employ a similar strategy to inhibit SG function. This study identifies an Arabidopsis thaliana NTF2-RRM domain-containing protein as a G3BP-like protein (AtG3BP), which localizes to plant SGs. Moreover, the nuclear shuttle protein (NSP) of the begomovirus abutilon mosaic virus (AbMV), which harbors a 'FVSF'-motif at its C-terminal end, interacts with the AtG3BP-like protein, as does the 'FNGSF'-motif containing NSP of pea necrotic yellow dwarf virus (PNYDV), a member of the Nanoviridae family. We therefore propose that SG formation upon stress is conserved between mammalian and plant cells and that plant viruses may follow a similar strategy to inhibit plant SG function as it has been shown for their mammalian counterparts. Copyright © 2016 Elsevier B.V. All rights reserved.

Short communication. First report of Eggplant mottled dwarf virus in China rose in southern Spain

Directory of Open Access Journals (Sweden)

G. Parrella

2013-01-01

Full Text Available Eggplant mottled dwarf virus (EMDV, genus Nucleorhabdovirus, family Rhabdoviridae is transmitted in nature by leafhoppers and its natural host range includes vegetable crops (eggplant, tomato, potato, pepper, ornamentals (pittosporum, honeysuckle, pelargonium and wild plants (caper, Solanum nigrum. The prevalence of infections is generally very low. EMDV has been demonstrated to be the causal agent of a vein yellowing disease of China rose (Hibiscus rosa-sinensis in southern Italy. In this work, four locations from Málaga and Granada provinces (southern Spain were surveyed in 2011 to study the prevalence of EMDV infections in China rose by serological and molecular methods. Overall, EMDV was detected in 77.3% of the samples (33 out of 45 samples tested. Mechanical transmission tests and immunoelectron microscopy confirmed the presence of EMDV. The possible causes of such a high and unexpected prevalence are discussed. The use of molecular hibridization with an EMDV specific riboprobe is proposed for early screening of vegetative propagated China rose plants to avoid dissemination of infected material.

Naming Disney's Dwarfs.

Science.gov (United States)

Sidwell, Robert T.

1980-01-01

Discusses Disney's version of the folkloric dwarfs in his production of "Snow White" and weighs the Disney rendition of the dwarf figure against the corpus of traits and behaviors pertaining to dwarfs in traditional folklore. Concludes that Disney's dwarfs are "anthropologically true." (HOD)

Effects of cover crops incorporation and nitrogen fertilization on N2O and CO2 emissions

Science.gov (United States)

Kandel, T. P.; Gowda, P. H.; Northup, B. K.; DuPont, J.; Somenahally, A. C.; Rocateli, A.

2017-12-01

In this study, we measured N2O and CO2 fluxes from plots planted to hairy vetch (winter cover crop) and broadleaf vetch (spring cover crop) as N sources for the following crabgrass (summer forage crop) in El Reno, Oklahoma, USA. Comparisons also included 0 and 60 kg ha-1 mineral N fertilizer supplied as dry urea. No significant N2O fluxes were observed during rapid growing periods of cover crops (March-April, 2017), however, large fluxes were observed after hairy vetch incorporation. Immediately after the hairy vetch biomass incorporation, large rainfall events were recorded. The fluxes subsided gradually with drying soil condition but were enhanced after every consecutive rainfall events. A rainfall induced flux measuring up to 8.2 kg N2O ha-1 day-1 was observed after 26 days of biomass incorporation. In total, 29 kg N2O ha-1 (18 kg N ha-1) was emitted within a month after biomass incorporation from hairy vetch plots. Growth of broadleaf vetch was poor and N2O fluxes were also lower. Similarly, plots fertilized with 60 kg N ha-1 had significant fluxes of N2O but the magnitude was much lower than the hairy vetch plots. Dynamics of N2O and CO fluxes correlated strongly. The results thus indicated that although cover crops may provide many environmental/agronomic benefits such as N fixation, soil carbon built-up, weed suppression and erosion control, high N2O emissions may dwarf these benefits.

Temperatures and luminosities of white dwarfs in dwarf novae

International Nuclear Information System (INIS)

Smak, J.

1984-01-01

Far ultraviolet radiation observed in dwarf novae at minimum can only be attributed to their white dwarfs. In three systems white dwarfs are detected directly through their eclipses. These data are used to determine the effective temperatures and luminosities of white dwarfs. The resulting temperatures range from about logT e = 4.1 to about 4.9, with typical values of about 4.5. The luminosities range from about logL 1 = 31.0 to about 33.5 and show correlation with the average accretion rates. Radiation from white dwarfs is likely to be the source of excitation of the emission lines from disks. It is also argued that the heating by the white dwarf can significantly modify the structure of the innermost parts of the disk and, particularly, inhibit the incidence of thermal instability in that region. 26 refs., 2 figs., 1 tab. (author)

Barley yellow dwarf virus Infection Leads to Higher Chemical Defense Signals and Lower Electrophysiological Reactions in Susceptible Compared to Tolerant Barley Genotypes.

Science.gov (United States)

Paulmann, Maria K; Kunert, Grit; Zimmermann, Matthias R; Theis, Nina; Ludwig, Anatoli; Meichsner, Doreen; Oelmüller, Ralf; Gershenzon, Jonathan; Habekuss, Antje; Ordon, Frank; Furch, Alexandra C U; Will, Torsten

2018-01-01

Barley yellow dwarf virus (BYDV) is a phloem limited virus that is persistently transmitted by aphids. Due to huge yield losses in agriculture, the virus is of high economic relevance. Since the control of the virus itself is not possible, tolerant barley genotypes are considered as the most effective approach to avoid yield losses. Although several genes and quantitative trait loci are known and used in barley breeding for virus tolerance, little is known about molecular and physiological backgrounds of this trait. Therefore, we compared the anatomy and early defense responses of a virus susceptible to those of a virus-tolerant cultivar. One of the very early defense responses is the transmission of electrophysiological reactions. Electrophysiological reactions to BYDV infection might differ between susceptible and tolerant cultivars, since BYDV causes disintegration of sieve elements in susceptible cultivars. The structure of vascular bundles, xylem vessels and sieve elements was examined using microscopy. All three were significantly decreased in size in infected susceptible plants where the virus causes disintegration of sieve elements. This could be associated with an uncontrolled ion exchange between the sieve-element lumen and apoplast. Further, a reduced electrophysiological isolation would negatively affect the propagation of electrophysiological reactions. To test the influence of BYDV infection on electrophysiological reactions, electropotential waves (EPWs) induced by leaf-tip burning were recorded using aphids as bioelectrodes. EPWs in infected susceptible plants disappeared already after 10 cm in contrast to those in healthy susceptible or infected tolerant or healthy tolerant plants. Another early plant defense reaction is an increase in reactive oxygen species (ROS). Using a fluorescent dye, we found a significant increase in ROS content in infected susceptible plants but not in infected tolerant plants. Similar results were found for the

Influence of Seeding Ratio, Planting Date, and Termination Date on Rye-Hairy Vetch Cover Crop Mixture Performance under Organic Management

OpenAIRE

Lawson, Andrew; Cogger, Craig; Bary, Andy; Fortuna, Ann-Marie

2015-01-01

Cover crop benefits include nitrogen accumulation and retention, weed suppression, organic matter maintenance, and reduced erosion. Organic farmers need region-specific information on winter cover crop performance to effectively integrate cover crops into their crop rotations. Our research objective was to compare cover crop seeding mixtures, planting dates, and termination dates on performance of rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth) monocultures and mixtures in the ma...

An unsuccessful search for brown dwarf companions to white dwarf stars

Science.gov (United States)

Shipman, Harry L.

1986-01-01

The results of a survey to detect excess infrared emission from white dwarf stars which would be attributable to a low mass companion are reviewed. Neither a simple comparison of spectroscopically identified white dwarf stars with the IRAS Point Source Catalog nor the coadding of IRAS survey data resulted in a detection of a brown dwarf. The seven nearest stars where the most stringent limits to the presence of a brown dwarf were obtained are listed, and an effort to detect brown dwarfs in the solar neighborhood is discussed.

Interactive Effects of Southern Rice Black-Streaked Dwarf Virus Infection of Host Plant and Vector on Performance of the Vector, Sogatella furcifera (Homoptera: Delphacidae).

Science.gov (United States)

Lei, Wenbin; Liu, Danfeng; Li, Pei; Hou, Maolin

2014-10-01

Performance of insect vectors can be influenced by the viruses they transmit, either directly by infection of the vectors or indirectly via infection of the host plants. Southern rice black-streaked dwarf virus (SRBSDV) is a propagative virus transmitted by the white-backed planthopper, Sogatella furcifera (Hovath). To elucidate the influence of SRBSDV on the performance of white-backed planthopper, life parameters of viruliferous and nonviruliferous white-backed planthopper fed rice seedlings infected or noninfected with SRBSDV were measured using a factorial design. Regardless of the infection status of the rice plant host, viruliferous white-backed planthopper nymphs took longer to develop from nymph to adult than did nonviruliferous nymphs. Viruliferous white-backed planthopper females deposited fewer eggs than nonviruliferous females and both viruliferous and nonviruliferous white-backed planthopper females laid fewer eggs on infected than on noninfected plants. Longevity of white-backed planthopper females was also affected by the infection status of the rice plant and white-backed planthopper. Nonviruliferous white-backed planthopper females that fed on infected rice plants lived longer than the other three treatment groups. These results indicate that the performance of white-backed planthopper is affected by SRBSDV either directly (by infection of white-backed planthopper) or indirectly (by infection of rice plant). The extended development of viruliferous nymphs and the prolonged life span of nonviruliferous adults on infected plants may increase their likelihood of transmitting virus, which would increase virus spread. © 2014 Entomological Society of America.

Influence of rice black streaked dwarf virus on the ecological fitness of non-vector planthopper Nilaparvata lugens (Hemiptera: Delphacidae).

Science.gov (United States)

Xu, Hong-Xing; He, Xiao-Chan; Zheng, Xu-Song; Yang, Ya-Jun; Lu, Zhong-Xian

2014-08-01

Rice black streak dwarf virus (RBSDV) is transmitted by the small brown planthopper (SBPH), Laodelphax striatellus (Fallen). Non-vector rice brown planthopper (BPH), Nilaparvata lugens (Stål), shares the same host rice plants with SBPH in paddy fields. The changes in nutritional composition of rice plants infected by RBSDV and the ecological fitness of BPH feeding on the infected plants were studied under both artificial climate chamber and field conditions. Contents of 16 detected amino acids and soluble sugar in RBSDV infected rice plants were higher than those in the healthy ones. On the diseased plants BPH had significantly higher nymphal survival rates, nymphal duration of the males, weight of the female adults, as well as egg hatchability compared to BPH being fed on healthy plants. However, there was no obvious difference in female nymph duration, longevity and fecundity. Defense enzymes (superoxidase dismutase, SOD and catalase, CAT) and detoxifying enzymes (carboxylesterase, CAE and glutathione S-transferase, GST) in BPH adults fed on diseased plants had markedly higher activities. The results indicate rice plants infected by RBSDV improved the ecological fitness of the brown planthopper, a serious pest but not a transmitter of the RBSDV virus. © 2013 Institute of Zoology, Chinese Academy of Sciences.

White dwarf radii and boundary-layer constraints in three dwarf novae

International Nuclear Information System (INIS)

Wood, J.H.

1990-01-01

The structure of the boundary layer between the accretion disc and white dwarf in three quiescent dwarf novae is explored with high signal-to-noise eclipse light curves obtained by phase folding 12-20 eclipses. Models of the eclipse shapes of various white dwarf/boundary layer configurations that might be at the centres of the accretion discs are calculated and compared with observations of the eclipses in Z Cha, OY Car and HT Cas. Possible models for the central objects are found to be a white dwarf with or without its lower hemisphere occulted by the disc, or a white dwarf with an optically thick boundary layer significantly extended in latitude up and down its sides. The most likely of these models for each system is an unocculted white dwarf with no boundary layer contributing significantly to the optical flux, or a white dwarf totally covered by an optically thick boundary layer. (author)

Identification and profiling of conserved and novel microRNAs in Laodelphax striatellus in response to rice black-streaked dwarf virus (RBSDV infection

Directory of Open Access Journals (Sweden)

Jun-Min Li

2015-03-01

Full Text Available MicroRNAs (miRNAs are small non-coding endogenous RNA molecules that play important roles in various biological processes. This study examined microRNA profiles of Laodelphax striatellus using the small RNA libraries derived from virus free (VF and rice black-streaked dwarf virus (RBSDV infected (RB insects. A total of 59 mature miRNAs (46 miRNA families were identified as conserved insect miRNAs in both VF and RB libraries. Among these conserved miRNAs, 24 were derived from the two arms of 12 miRNA precursors. Nine conserved L. striatellus miRNAs were up-regulated and 12 were down-regulated in response to RBSDV infection. In addition, a total of 20 potential novel miRNA candidates were predicted in the VF and RB libraries. The miRNA transcriptome profiles and the identification of L. striatellus miRNAs differentially expressed in response to RBSDV infection will contribute to future studies to elucidate the complex miRNA-mediated regulatory network activated by pathogen challenge in insect vectors.

SATELLITE DWARF GALAXIES IN A HIERARCHICAL UNIVERSE: THE PREVALENCE OF DWARF-DWARF MAJOR MERGERS

OpenAIRE

Deason, A; Wetzel, A; Garrison-Kimmel, S

2014-01-01

Mergers are a common phenomenon in hierarchical structure formation, especially for massive galaxies and clusters, but their importance for dwarf galaxies in the Local Group remains poorly understood. We investigate the frequency of major mergers between dwarf galaxies in the Local Group using the ELVIS suite of cosmological zoom-in dissipationless simulations of Milky Way- and M31-like host halos. We find that ~10% of satellite dwarf galaxies with M_star > 10^6 M_sun that are within the host...

In vitro synthesis of minus-strand RNA by an isolated cereal yellow dwarf virus RNA-dependent RNA polymerase requires VPg and a stem-loop structure at the 3' end of the virus RNA.

Science.gov (United States)

Osman, Toba A M; Coutts, Robert H A; Buck, Kenneth W

2006-11-01

Cereal yellow dwarf virus (CYDV) RNA has a 5'-terminal genome-linked protein (VPg). We have expressed the VPg region of the CYDV genome in bacteria and used the purified protein (bVPg) to raise an antiserum which was able to detect free VPg in extracts of CYDV-infected oat plants. A template-dependent RNA-dependent RNA polymerase (RdRp) has been produced from a CYDV membrane-bound RNA polymerase by treatment with BAL 31 nuclease. The RdRp was template specific, being able to utilize templates from CYDV plus- and minus-strand RNAs but not those of three unrelated viruses, Red clover necrotic mosaic virus, Cucumber mosaic virus, and Tobacco mosaic virus. RNA synthesis catalyzed by the RdRp required a 3'-terminal GU sequence and the presence of bVPg. Additionally, synthesis of minus-strand RNA on a plus-strand RNA template required the presence of a putative stem-loop structure near the 3' terminus of CYDV RNA. The base-paired stem, a single-nucleotide (A) bulge in the stem, and the sequence of a tetraloop were all required for the template activity. Evidence was produced showing that minus-strand synthesis in vitro was initiated by priming by bVPg at the 3' end of the template. The data are consistent with a model in which the RdRp binds to the stem-loop structure which positions the active site to recognize the 3'-terminal GU sequence for initiation of RNA synthesis by the addition of an A residue to VPg.

White dwarf heating and the ultraviolet flux in dwarf novae

International Nuclear Information System (INIS)

Pringle, J.E.

1988-01-01

An investigation is made of the heating of the outer layers of the white dwarf which is likely to occur during a dwarf nova outburst. It is shown that the decline in IUE flux, observed during quiescent intervals in the dwarf novae VW Hydri and WX Hydri, may be due to the outer layers cooling off once the heat source is removed. The calculations here assume uniformity of the heat source over the white dwarf surface. This is unlikely to be realized from disc accretion, and we discuss that further calculations are required. (author)

Searching for benchmark systems containing ultra-cool dwarfs and white dwarfs

Directory of Open Access Journals (Sweden)

Pinfield D.J.

2013-04-01

Full Text Available We have used the 2MASS all-sky survey and WISE to look for ultracool dwarfs that are part of multiple systems containing main sequence stars. We cross-matched L dwarf candidates from the surveys with Hipparcos and Gliese stars, finding two new systems. We consider the binary fraction for L dwarfs and main sequence stars, and further assess possible unresolved multiplicity within the full companion sample. This analysis shows that some of the L dwarfs in this sample might actually be unresolved binaries themselves. We have also identified a sample of common proper motion systems in which a main sequence star has a white dwarf as wide companion. These systems can help explore key issues in star evolution theory, as the initial-final mass relationship of white dwarfs, or the chromospheric activity-age relationship for stars still in the main sequence. Spectroscopy for 50 white dwarf candidates, selected from the SuperCOSMOS Science Archive, was obtained. We have also observed 6 of the main sequence star companions, and have estimated their effective temperatures, rotational and microturbulent velocities and metallicities.

Label-Free Quantitative Proteomic Analysis of Chitosan Oligosaccharide-Treated Rice Infected with Southern Rice Black-Streaked Dwarf Virus.

Science.gov (United States)

Yang, Anming; Yu, Lu; Chen, Zhuo; Zhang, Shanxue; Shi, Jing; Zhao, Xiaozhen; Yang, Yuanyou; Hu, Deyu; Song, Baoan

2017-05-18

Southern rice black-streaked dwarf virus (SRBSDV) has spread from thesouth of China to the north of Vietnam in the past few years and severelyinfluenced rice production. Its long incubation period and early symptoms are not evident; thus, controlling it is difficult. Chitosan oligosaccharide (COS) is a green plant immunomodulator. Early studies showed that preventing and controlling SRBSDV have a certain effect and reduce disease infection rate, but its underlying controlling and preventing mechanism is unclear. In this study, label-free proteomics was used to analyze differentially expressed proteins in rice after COS treatment. The results showed that COS can up-regulate the plant defense-related proteins and down-regulate the protein expression levels of SRBSDV. Meanwhile, quantitative real-time PCR test results showed that COS can improve defense gene expression in rice. Moreover, COS can enhance the defense enzymatic activities of peroxidase, superoxide dismutase and catalase through mitogen-activated protein kinase signaling cascade pathway, and enhance the rice disease resistance.

An integrated protein localization and interaction map for Potato yellow dwarf virus, type species of the genus Nucleorhabdovirus

International Nuclear Information System (INIS)

Bandyopadhyay, Anindya; Kopperud, Kristin; Anderson, Gavin; Martin, Kathleen; Goodin, Michael

2010-01-01

The genome of Potato yellow dwarf virus (PYDV; Nucleorhabdovirus type species) was determined to be 12,875 nucleotides (nt). The antigenome is organized into seven open reading frames (ORFs) ordered 3'-N-X-P-Y-M-G-L-5', which likely encode the nucleocapsid, phospho, movement, matrix, glyco and RNA-dependent RNA polymerase proteins, respectively, except for X, which is of unknown function. The ORFs are flanked by a 3' leader RNA of 149 nt and a 5' trailer RNA of 97 nt, and are separated by conserved intergenic junctions. Phylogenetic analyses indicated that PYDV is closely related to other leafhopper-transmitted rhabdoviruses. Functional protein assays were used to determine the subcellular localization of PYDV proteins. Surprisingly, the M protein was able to induce the intranuclear accumulation of the inner nuclear membrane in the absence of any other viral protein. Finally, bimolecular fluorescence complementation was used to generate the most comprehensive protein interaction map for a plant-adapted rhabdovirus to date.

FIRST DIRECT EVIDENCE THAT BARIUM DWARFS HAVE WHITE DWARF COMPANIONS

International Nuclear Information System (INIS)

Gray, R. O.; McGahee, C. E.; Griffin, R. E. M.; Corbally, C. J.

2011-01-01

Barium II (Ba) stars are chemically peculiar F-, G-, and K-type objects that show enhanced abundances of s-process elements. Since s-process nucleosynthesis is unlikely to take place in stars prior to the advanced asymptotic giant branch (AGB) stage, the prevailing hypothesis is that each present Ba star was contaminated by an AGB companion which is now a white dwarf (WD). Unless the initial mass ratio of such a binary was fairly close to unity, the receiving star is thus at least as likely to be a dwarf as a giant. So although most known Ba stars appear to be giants, the hypothesis requires that Ba dwarfs be comparably plentiful and moreover that they should all have WD companions. However, despite dedicated searches with the IUE satellite, no WD companions have been directly detected to date among the classical Ba dwarfs, even though some 90% of those stars are spectroscopic binaries, so the contamination hypothesis is therefore presently in some jeopardy. In this paper, we analyze recent deep, near-UV and far-UV Galaxy Evolution Explorer (GALEX) exposures of four of the brightest of the class (HD 2454, 15360, 26367, and 221531), together with archived GALEX data for two newly recognized Ba dwarfs: HD 34654 and HD 114520 (which also prove to be spectroscopic binaries). The GALEX observations of the Ba dwarfs as a group show a significant far-UV excess compared to a control sample of normal F-type dwarfs. We suggest that this ensemble far-UV excess constitutes the first direct evidence that Ba dwarfs have WD companions.

White Dwarf Stars

OpenAIRE

Kepler, S. O.; Romero, Alejandra Daniela; Pelisoli, Ingrid; Ourique, Gustavo

2017-01-01

White dwarf stars are the final stage of most stars, born single or in multiple systems. We discuss the identification, magnetic fields, and mass distribution for white dwarfs detected from spectra obtained by the Sloan Digital Sky Survey up to Data Release 13 in 2016, which lead to the increase in the number of spectroscopically identified white dwarf stars from 5000 to 39000. This number includes only white dwarf stars with log g >= 6.5 stars, i.e., excluding the Extremely Low Mass white dw...

Radiation of dwarf novae

International Nuclear Information System (INIS)

Bruch, A.

1987-01-01

The nature of dwarf novae with their components white dwarf star, cool star, accretion disk, boundary layer and hot spot is investigated. It is shown that very different physical states and processes occur in the components of dwarf novae. Spectroscopical and photometrical observations are carried out. For better understanding the radiation portions of the single dwarf novae components are separated from the total electromagnetic spectrum recieved from the dwarf novae. The model assumptions are compared with the observations and verified

Identification of virus isolates inducing mosaic of sugarcane in ...

African Journals Online (AJOL)

SAM

2014-03-19

Mar 19, 2014 ... (JGMV), maize dwarf mosaic virus (MDMV) and sorghum mosaic Virus (SrMV) is an economically important viral disease of sugarcane ... race (“Bahausa”) and the least infected was the white land race (“fararkwama”). ... stripes symptoms on leaf blade and white stripe on stem in infected sugarcane and are ...

WHITE DWARF/M DWARF BINARIES AS SINGLE DEGENERATE PROGENITORS OF TYPE Ia SUPERNOVAE

International Nuclear Information System (INIS)

Wheeler, J. Craig

2012-01-01

Limits on the companions of white dwarfs in the single-degenerate scenario for the origin of Type Ia supernovae (SNe Ia) have gotten increasingly tight, yet igniting a nearly Chandrasekhar mass C/O white dwarf from a condition of near hydrostatic equilibrium provides compelling agreement with observed spectral evolution. The only type of non-degenerate stars that survive the tight limits, M V ∼> 8.4 on the SN Ia in SNR 0509-67.5 and M V ∼> 9.5 in the remnant of SN 1572, are M dwarfs. While M dwarfs are observed in cataclysmic variables, they have special properties that have not been considered in most work on the progenitors of SNe Ia: they have small but finite magnetic fields and they flare frequently. These properties are explored in the context of SN Ia progenitors. White dwarf/M dwarf pairs may be sufficiently plentiful to provide, in principle, an adequate rate of explosions even with slow orbital evolution due to magnetic braking or gravitational radiation. Even modest magnetic fields on the white dwarf and M dwarf will yield adequate torques to lock the two stars together, resulting in a slowly rotating white dwarf, with the magnetic poles pointing at one another in the orbital plane. The mass loss will be channeled by a 'magnetic bottle' connecting the two stars, landing on a concentrated polar area on the white dwarf. This enhances the effective rate of accretion compared to spherical accretion. Luminosity from accretion and hydrogen burning on the surface of the white dwarf may induce self-excited mass transfer. The combined effects of self-excited mass loss, polar accretion, and magnetic inhibition of mixing of accretion layers give possible means to beat the 'nova limit' and grow the white dwarf to the Chandrasekhar mass even at rather moderate mass accretion rates.

VARIABILITY OF LENGTH OF STEM OF DETERMINATE AND INDETERMINATE CULTIVARS OF COMMON VETCH (VICIA SATIVA L. SSP. SATIVA AND ITS IMPACT ON SELECTED CROPPING FEATURES

Directory of Open Access Journals (Sweden)

Jadwiga ANDRZEJEWSKA

2006-12-01

Full Text Available In the years 2001 and 2002, the study was conducted in six experiments in order to examine the conditioning of the length of stem variability and its impact on cropping features of determinate and indeterminate cultivars of common vetch. Rainfall in June and July as well as during the whole growing season was positively correlated with length of stem, but negatively correlated with seed yield, to a larger extent in the group of indeterminate cultivars than in the determinate one. Duration of blooming stage, length of stem, and seed yield showed the largest variability in both groups. Increase in length of stem of plants of indeterminate cultivars led to the delay in maturation, to less even maturation, and to the decrease in the thousand seed weight and seed yield. Increase in length of stem of plants of determinate cultivars delayed reaching the phase of technical maturation and decreased evenness of plant maturation. Determinate growth of common vetch did not lead to the reduction of lodging.

FORMATION OF ULTRA-COMPACT BLUE DWARF GALAXIES AND THEIR EVOLUTION INTO NUCLEATED DWARFS

International Nuclear Information System (INIS)

Bekki, Kenji

2015-01-01

We propose that there is an evolutionary link between ultra-compact blue dwarf galaxies (UCBDs) with active star formation and nucleated dwarfs based on the results of numerical simulations of dwarf–dwarf merging. We consider the observational fact that low-mass dwarfs can be very gas-rich, and thereby investigate the dynamical and chemical evolution of very gas-rich, dissipative dwarf–dwarf mergers. We find that the remnants of dwarf–dwarf mergers can be dominated by new stellar populations formed from the triggered starbursts and consequently can have blue colors and higher metallicities (Z ∼ [0.2–1]Z ⊙ ). We also find that the remnants of these mergers can have rather high mass densities (10 4 M ⊙ pc −3 ) within the central 10 pc and small half-light radii (40−100 pc). The radial stellar structures of some merger remnants are similar to those of nucleated dwarfs. Star formation can continue in nuclear gas disks (R < 100 pc) surrounding stellar galactic nuclei (SGNs) so that the SGNs can finally have multiple stellar populations with different ages and metallicities. These very compact blue remnants can be identified as UCBDs soon after merging and as nucleated dwarfs after the young stars fade. We discuss these results in the context of the origins of metal-rich ultra-compact dwarfs and SGNs

FORMATION OF ULTRA-COMPACT BLUE DWARF GALAXIES AND THEIR EVOLUTION INTO NUCLEATED DWARFS

Energy Technology Data Exchange (ETDEWEB)

Bekki, Kenji [ICRAR, M468, The University of Western Australia 35 Stirling Highway, Crawley Western Australia, 6009 (Australia)

2015-10-10

We propose that there is an evolutionary link between ultra-compact blue dwarf galaxies (UCBDs) with active star formation and nucleated dwarfs based on the results of numerical simulations of dwarf–dwarf merging. We consider the observational fact that low-mass dwarfs can be very gas-rich, and thereby investigate the dynamical and chemical evolution of very gas-rich, dissipative dwarf–dwarf mergers. We find that the remnants of dwarf–dwarf mergers can be dominated by new stellar populations formed from the triggered starbursts and consequently can have blue colors and higher metallicities (Z ∼ [0.2–1]Z{sub ⊙}). We also find that the remnants of these mergers can have rather high mass densities (10{sup 4} M{sub ⊙} pc{sup −3}) within the central 10 pc and small half-light radii (40−100 pc). The radial stellar structures of some merger remnants are similar to those of nucleated dwarfs. Star formation can continue in nuclear gas disks (R < 100 pc) surrounding stellar galactic nuclei (SGNs) so that the SGNs can finally have multiple stellar populations with different ages and metallicities. These very compact blue remnants can be identified as UCBDs soon after merging and as nucleated dwarfs after the young stars fade. We discuss these results in the context of the origins of metal-rich ultra-compact dwarfs and SGNs.

New Light on Dark Stars Red Dwarfs, Low-Mass Stars, Brown Dwarfs

CERN Document Server

Reid, I. Neill

2005-01-01

There has been very considerable progress in research into low-mass stars, brown dwarfs and extrasolar planets during the past few years, particularly since the fist edtion of this book was published in 2000. In this new edtion the authors present a comprehensive review of both the astrophysical nature of individual red dwarf and brown dwarf stars and their collective statistical properties as an important Galactic stellar population. Chapters dealing with the observational properies of low-mass dwarfs, the stellar mass function and extrasolar planets have been completely revised. Other chapters have been significantly revised and updated as appropriate, including important new material on observational techniques, stellar acivity, the Galactic halo and field star surveys. The authors detail the many discoveries of new brown dwarfs and extrasolar planets made since publication of the first edition of the book and provide a state-of-the-art review of our current knowledge of very low-mass stars, brown dwarfs a...

Distinguishing CDM dwarfs from SIDM dwarfs in baryonic simulations

Science.gov (United States)

Strickland, Emily; Fitts, Alex B.; Boylan-Kolchin, Michael

2017-06-01

Dwarf galaxies in the nearby Universe are the most dark-matter-dominated systems known. They are therefore natural probes of the nature of dark matter, which remains unknown. Our collaboration has performed several high-resolution cosmological zoom-in simulations of isolated dwarf galaxies. We simulate each galaxy in standard cold dark matter (ΛCDM) as well as self-interacting dark matter (SIDM, with a cross section of σ/m ~ 1 cm2/g), both with and without baryons, in order to identify distinguishing characteristics between the two. The simulations are run using GIZMO, a meshless-finite-mass hydrodynamical code, and are part of the Feedback in Realistic Environments (FIRE) project. By analyzing both the global properties and inner structure of the dwarfs in varying dark matter prescriptions, we provide a side-by-side comparison of isolated, dark-matter-dominated galaxies at the mass scale where differences in the two models of dark matter are thought to be the most obvious. We find that the edge of classical dwarfs and ultra-faint dwarfs (at stellar masses of ~105 solar masses) provides the clearest window for distinguishing between the two theories. At these low masses, our SIDM galaxies have a cored inner density profile, while their CDM counterparts have “cuspy” centers. The SIDM versions of each galaxy also have measurably lower stellar velocity dispersions than their CDM counterparts. Future observations of ultra faint dwarfs with JWST and 30-m telescopes will be able to discern whether such alternate theories of dark matter are viable.

THE BROWN DWARF KINEMATICS PROJECT (BDKP). III. PARALLAXES FOR 70 ULTRACOOL DWARFS

International Nuclear Information System (INIS)

Faherty, Jacqueline K.; Shara, Michael M.; Cruz, Kelle L.; Burgasser, Adam J.; Walter, Frederick M.; Van der Bliek, Nicole; West, Andrew A.; Vrba, Frederick J.; Anglada-Escudé, Guillem

2012-01-01

We report parallax measurements for 70 ultracool dwarfs (UCDs) including 11 late-M, 32 L, and 27 T dwarfs. In this sample, 14 M and L dwarfs exhibit low surface gravity features, 6 are close binary systems, and 2 are metal-poor subdwarfs. We combined our new measurements with 114 previously published UCD parallaxes and optical-mid-IR photometry to examine trends in spectral-type/absolute magnitude, and color-color diagrams. We report new polynomial relations between spectral type and M JHK . Including resolved L/T transition binaries in the relations, we find no reason to differentiate between a 'bright' (unresolved binary) and a 'faint' (single source) sample across the L/T boundary. Isolating early T dwarfs, we find that the brightening of T0-T4 sources is prominent in M J where there is a [1.2-1.4] mag difference. A similar yet dampened brightening of [0.3-0.5] mag happens at M H and a plateau or dimming of [–0.2 to –0.3] mag is seen in M K . Comparison with evolutionary models that vary gravity, metallicity, and cloud thickness verifies that for L into T dwarfs, decreasing cloud thickness reproduces brown dwarf near-IR color-magnitude diagrams. However we find that a near constant temperature of 1200 ±100 K along a narrow spectral subtype of T0-T4 is required to account for the brightening and color-magnitude diagram of the L-dwarf/T-dwarf transition. There is a significant population of both L and T dwarfs which are red or potentially 'ultra-cloudy' compared to the models, many of which are known to be young indicating a correlation between enhanced photospheric dust and youth. For the low surface gravity or young companion L dwarfs we find that 8 out of 10 are at least [0.2-1.0] mag underluminous in M JH and/or M K compared to equivalent spectral type objects. We speculate that this is a consequence of increased dust opacity and conclude that low surface gravity L dwarfs require a completely new spectral-type/absolute magnitude polynomial for analysis.

THE BROWN DWARF KINEMATICS PROJECT (BDKP). III. PARALLAXES FOR 70 ULTRACOOL DWARFS

Energy Technology Data Exchange (ETDEWEB)

Faherty, Jacqueline K.; Shara, Michael M.; Cruz, Kelle L. [Department of Astrophysics, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10034 (United States); Burgasser, Adam J. [Center of Astrophysics and Space Sciences, Department of Physics, University of California, San Diego, CA 92093 (United States); Walter, Frederick M. [Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794-3800 (United States); Van der Bliek, Nicole [CTIO/National Optical Astronomy Observatory (Chile); West, Andrew A. [Department of Astronomy, Boston University, 725 Commonwealth Ave Boston, MA 02215 (United States); Vrba, Frederick J. [US Naval Observatory, Flagstaff Station, P.O. Box 1149, Flagstaff, AZ 86002 (United States); Anglada-Escude, Guillem, E-mail: jfaherty@amnh.org [Department of Terrestrial Magnetism, Carnegie Institution of Washington 5241 Broad Branch Road, NW, Washington, DC 20015 (United States)

2012-06-10

We report parallax measurements for 70 ultracool dwarfs (UCDs) including 11 late-M, 32 L, and 27 T dwarfs. In this sample, 14 M and L dwarfs exhibit low surface gravity features, 6 are close binary systems, and 2 are metal-poor subdwarfs. We combined our new measurements with 114 previously published UCD parallaxes and optical-mid-IR photometry to examine trends in spectral-type/absolute magnitude, and color-color diagrams. We report new polynomial relations between spectral type and M{sub JHK}. Including resolved L/T transition binaries in the relations, we find no reason to differentiate between a 'bright' (unresolved binary) and a 'faint' (single source) sample across the L/T boundary. Isolating early T dwarfs, we find that the brightening of T0-T4 sources is prominent in M{sub J} where there is a [1.2-1.4] mag difference. A similar yet dampened brightening of [0.3-0.5] mag happens at M{sub H} and a plateau or dimming of [-0.2 to -0.3] mag is seen in M{sub K} . Comparison with evolutionary models that vary gravity, metallicity, and cloud thickness verifies that for L into T dwarfs, decreasing cloud thickness reproduces brown dwarf near-IR color-magnitude diagrams. However we find that a near constant temperature of 1200 {+-}100 K along a narrow spectral subtype of T0-T4 is required to account for the brightening and color-magnitude diagram of the L-dwarf/T-dwarf transition. There is a significant population of both L and T dwarfs which are red or potentially 'ultra-cloudy' compared to the models, many of which are known to be young indicating a correlation between enhanced photospheric dust and youth. For the low surface gravity or young companion L dwarfs we find that 8 out of 10 are at least [0.2-1.0] mag underluminous in M{sub JH} and/or M{sub K} compared to equivalent spectral type objects. We speculate that this is a consequence of increased dust opacity and conclude that low surface gravity L dwarfs require a completely new

Activity and Kinematics of White Dwarf-M Dwarf Binaries from the SUPERBLINK Proper Motion Survey

International Nuclear Information System (INIS)

Skinner, Julie N.; Morgan, Dylan P.; West, Andrew A.; Lépine, Sébastien; Thorstensen, John R.

2017-01-01

We present an activity and kinematic analysis of high proper motion white dwarf-M dwarf binaries (WD+dMs) found in the SUPERBLINK survey, 178 of which are new identifications. To identify WD+dMs, we developed a UV–optical–IR color criterion and conducted a spectroscopic survey to confirm each candidate binary. For the newly identified systems, we fit the two components using model white dwarf spectra and M dwarf template spectra to determine physical parameters. We use H α chromospheric emission to examine the magnetic activity of the M dwarf in each system, and investigate how its activity is affected by the presence of a white dwarf companion. We find that the fraction of WD+dM binaries with active M dwarfs is significantly higher than their single M dwarf counterparts at early and mid-spectral types. We corroborate previous studies that find high activity fractions at both close and intermediate separations. At more distant separations, the binary fraction appears to approach the activity fraction for single M dwarfs. Using derived radial velocities and the proper motions, we calculate 3D space velocities for the WD+dMs in SUPERBLINK. For the entire SUPERBLINK WD+dMs, we find a large vertical velocity dispersion, indicating a dynamically hotter population compared to high proper motion samples of single M dwarfs. We compare the kinematics for systems with active M dwarfs and those with inactive M dwarfs, and find signatures of asymmetric drift in the inactive sample, indicating that they are drawn from an older population.

Activity and Kinematics of White Dwarf-M Dwarf Binaries from the SUPERBLINK Proper Motion Survey

Energy Technology Data Exchange (ETDEWEB)

Skinner, Julie N. [Institute for Astrophysical Research, Boston University, 725 Commonwealth Avenue, Boston, MA 02215 (United States); Morgan, Dylan P.; West, Andrew A. [Department of Astronomy, Boston University, 725 Commonwealth Avenue, Boston, MA 02215 (United States); Lépine, Sébastien [Department of Physics and Astronomy, Georgia State University, 25 Park Place NE, Atlanta, GA, 30303 (United States); Thorstensen, John R., E-mail: jskinner@bu.edu [Department of Physics and Astronomy, 6127 Wilder Laboratory, Dartmouth College, Hanover, NH 03755 (United States)

2017-09-01

We present an activity and kinematic analysis of high proper motion white dwarf-M dwarf binaries (WD+dMs) found in the SUPERBLINK survey, 178 of which are new identifications. To identify WD+dMs, we developed a UV–optical–IR color criterion and conducted a spectroscopic survey to confirm each candidate binary. For the newly identified systems, we fit the two components using model white dwarf spectra and M dwarf template spectra to determine physical parameters. We use H α chromospheric emission to examine the magnetic activity of the M dwarf in each system, and investigate how its activity is affected by the presence of a white dwarf companion. We find that the fraction of WD+dM binaries with active M dwarfs is significantly higher than their single M dwarf counterparts at early and mid-spectral types. We corroborate previous studies that find high activity fractions at both close and intermediate separations. At more distant separations, the binary fraction appears to approach the activity fraction for single M dwarfs. Using derived radial velocities and the proper motions, we calculate 3D space velocities for the WD+dMs in SUPERBLINK. For the entire SUPERBLINK WD+dMs, we find a large vertical velocity dispersion, indicating a dynamically hotter population compared to high proper motion samples of single M dwarfs. We compare the kinematics for systems with active M dwarfs and those with inactive M dwarfs, and find signatures of asymmetric drift in the inactive sample, indicating that they are drawn from an older population.

Activity and Kinematics of White Dwarf-M Dwarf Binaries from the SUPERBLINK Proper Motion Survey

Science.gov (United States)

Skinner, Julie N.; Morgan, Dylan P.; West, Andrew A.; Lépine, Sébastien; Thorstensen, John R.

2017-09-01

We present an activity and kinematic analysis of high proper motion white dwarf-M dwarf binaries (WD+dMs) found in the SUPERBLINK survey, 178 of which are new identifications. To identify WD+dMs, we developed a UV-optical-IR color criterion and conducted a spectroscopic survey to confirm each candidate binary. For the newly identified systems, we fit the two components using model white dwarf spectra and M dwarf template spectra to determine physical parameters. We use Hα chromospheric emission to examine the magnetic activity of the M dwarf in each system, and investigate how its activity is affected by the presence of a white dwarf companion. We find that the fraction of WD+dM binaries with active M dwarfs is significantly higher than their single M dwarf counterparts at early and mid-spectral types. We corroborate previous studies that find high activity fractions at both close and intermediate separations. At more distant separations, the binary fraction appears to approach the activity fraction for single M dwarfs. Using derived radial velocities and the proper motions, we calculate 3D space velocities for the WD+dMs in SUPERBLINK. For the entire SUPERBLINK WD+dMs, we find a large vertical velocity dispersion, indicating a dynamically hotter population compared to high proper motion samples of single M dwarfs. We compare the kinematics for systems with active M dwarfs and those with inactive M dwarfs, and find signatures of asymmetric drift in the inactive sample, indicating that they are drawn from an older population. Based on observations obtained at the MDM Observatory operated by Dartmouth College, Columbia University, The Ohio State University, and the University of Michigan.

37 NEW T-TYPE BROWN DWARFS IN THE CANADA-FRANCE BROWN DWARFS SURVEY

International Nuclear Information System (INIS)

Albert, Loic; Artigau, Etienne; Delorme, Philippe; Reyle, Celine; Forveille, Thierry; Delfosse, Xavier; Willott, Chris J.

2011-01-01

The Canada-France Brown Dwarfs Survey is an i'- and z'-band survey realized with MegaCam at the Canada-France-Hawaii Telescope that covers a surface area of 780 deg 2 . Image analysis is now completed while J-band follow-up campaigns are ∼90% done. The survey identified about 70 T dwarf candidates, of which 43 now have near-infrared spectra obtained with NIRI and GNIRS at Gemini and ISAAC at the Very Large Telescope. Six of these were previously published and we present here the 37 new discoveries, all T dwarfs. They range from T0 to T8.5 with four being of type T7 or later. Both newly identified T8 dwarfs are possibly high log (g) massive brown dwarfs of thin disk age. One T4.5 dwarf shows signs of sub-metallicity. We present proper motions and near-infrared photometry, and discuss about the most peculiar/interesting objects in some details.

Mid-Infrared Observations of the White Dwarf Brown Dwarf Binary GD 1400

OpenAIRE

Farihi, J.; Zuckerman, B.; Becklin, E. E.

2005-01-01

Fluxes are measured for the DA white dwarf plus brown dwarf pair GD 1400 with the Infrared Array Camera on the {\\em Spitzer Space Telescope}. GD 1400 displays an infrared excess over the entire $3-8\\mu$m region consistent with the presence of a mid- to late-type L dwarf companion. A discussion is given regarding current knowledge of this unique system.

Epidemiology and integrated management of persistently transmitted aphid-borne viruses of legume and cereal crops in West Asia and North Africa.

Science.gov (United States)

Makkouk, Khaled M; Kumari, Safaa G

2009-05-01

Cool-season food legumes (faba bean, lentil, chickpea and pea) and cereals (bread and durum wheat and barley) are the most important and widely cultivated crops in West Asia and North Africa (WANA), where they are the main source of carbohydrates and protein for the majority of the population. Persistently transmitted aphid-borne viruses pose a significant limitation to legume and cereal production worldwide. Surveys conducted in many countries in WANA during the last three decades established that the most important of these viruses are: Faba bean necrotic yellows virus (FBNYV: genus Nanovirus; family Nanoviridae), Bean leafroll virus (BLRV: genus Luteovirus; family Luteoviridae), Beet western yellows virus (BWYV: genus Polerovirus; family Luteoviridae), Soybean dwarf virus (SbDV: genus Luteovirus; family Luteoviridae) and Chickpea chlorotic stunt virus (CpCSV: genus Polerovirus; family Luteoviridae) which affect legume crops, and Barley yellow dwarf virus-PAV (BYDV-PAV: genus Luteovirus; family Luteoviridae), Barley yellow dwarf virus-MAV (BYDV-MAV: genus Luteovirus; family Luteoviridae) and Cereal yellow dwarf virus-RPV (CYDV-RPV: genus Polerovirus; family Luteoviridae) which affect cereal crops. Loss in yield caused by these viruses is usually high when infection occurs early in the growing season. Many aphid vector species for the above-mentioned viruses are reported to be prevalent in the WANA region. In addition, in this region many wild species (annual or perennial) were found infected with these viruses and may play an important role in their ecology and spread. Fast spread of these diseases was always associated with high aphid vector populations and activity. Although virus disease management can be achieved by combining several control measures, development of resistant genotypes is undoubtedly one of the most appropriate control methods. Over the last three decades barley and wheat genotypes resistant to BYDV, faba bean genotypes resistant to BLRV, and

Stark Broadening and White Dwarfs

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Dimitrijević Milan S.

2011-12-01

Full Text Available White dwarf and pre-white dwarfs are the best types of stars for the application of Stark broadening research results in astrophysics, since in the atmospheres of these stars physical conditions are very favorable for this line broadening mechanism - in hot hydrogen-deficient white dwarfs and pre-white dwarfs Teff = 75 000–180 000 K and log g = 5.5–8 [cgs]. Even for much cooler DA and DB white dwarfs with the typical effective temperatures 10 000-20 000 K, Stark broadening is usually the dominant broadening mechanism. In this review, Stark broadening in white dwarf spectra is considered, and the attention is drawn to the STARK-B database (http://stark-b.obspm.fr/, containing the parameters needed for analysis and synthesis of white dwarf spectra, as well as for the collective efforts to develop the Virtual Atomic and Molecular Data Center.

Dwarf Mice and Aging.

Science.gov (United States)

Masternak, Michal M; Darcy, Justin; Victoria, Berta; Bartke, Andrzej

2018-01-01

Dwarf mice have been studied for many decades, however, the focus of these studies shifted in 1996 when it was shown by Brown-Borg and her coworkers that Ames dwarf (Prop1 df ) mice are exceptionally long-lived. Since then, Snell dwarf (Pit1 dw ) and growth hormone receptor knockout (GHR-KO, a.k.a. Laron dwarf) mice were also shown to be exceptionally long-lived, presumably due to their growth hormone (GH)-deficiency or -resistance, respectively. What is of equal importance in these dwarf mice is their extended health span, that is, these animals have a longer period of life lived free of frailty and age-related diseases. This review article focuses on recent studies conducted in these dwarf mice, which concerned brown and white adipose tissue biology, microRNA (miRNA) profiling, as well as early-life dietary and hormonal interventions. Results of these studies identify novel mechanisms linking reduced GH action with extensions of both life span and health span. Copyright © 2017. Published by Elsevier Inc.

Benchmarking Brown Dwarf Models With a Non-irradiated Transiting Brown Dwarf in Praesepe

Science.gov (United States)

Beatty, Thomas; Marley, Mark; Line, Michael; Gizis, John

2018-05-01

We wish to use 9.4 hours of Spitzer time to observe two eclipses, one each at 3.6um and 4.5um, of the transiting brown dwarf AD 3116b. AD 3116b is a 54.2+/-4.3 MJ, 1.08+/-0.07 RJ object on a 1.98 day orbit about a 3200K M-dwarf. Uniquely, AD 3116 and its host star are both members of Praesepe, a 690+/-60 Myr old open cluster. AD 3116b is thus one of two transiting brown dwarfs for which we have a robust isochronal age that is not dependent upon brown dwarf evolutionary models, and the youngest brown dwarf for which this is the case. Importantly, the flux AD 3116b receives from its host star is only 0.7% of its predicted internal luminosity (Saumon & Marley 2008). This makes AD 3116b the first known transiting brown dwarf that simultaneously has a well-defined age, and that receives a negligible amount of external irradiation, and a unique laboratory to test radius and luminosity predictions from brown dwarf evolutionary models. Our goal is to measure the emission from the brown dwarf. AD 3116b should have large, 25 mmag, eclipse depths in the Spitzer bandpasses, and we expect to measure them with a precision of +/-0.50 mmag at 3.6um and +/-0.54 mmag at 4.5um. This will allow us to make measure AD 3116b?s internal effective temperature to +/-40K. We will also use the upcoming Gaia DR2 parallaxes to measure AD 3116b's absolute IRAC magnitudes and color, and hence determine the cloud properties of the atmosphere. As the only known brown dwarf with an independently measured mass, radius, and age, Spitzer measurements of AD 3116b's luminosity and clouds will provide a critical benchmark for brown dwarf observation and theory.

Variation in Susceptibility to Wheat dwarf virus among Wild and Domesticated Wheat

Science.gov (United States)

Nygren, Jim; Shad, Nadeem; Kvarnheden, Anders; Westerbergh, Anna

2015-01-01

We investigated the variation in plant response in host-pathogen interactions between wild (Aegilops spp., Triticum spp.) and domesticated wheat (Triticum spp.) and Wheat dwarf virus (WDV). The distribution of WDV and its wild host species overlaps in Western Asia in the Fertile Crescent, suggesting a coevolutionary relationship. Bread wheat originates from a natural hybridization between wild emmer wheat (carrying the A and B genomes) and the wild D genome donor Aegilops tauschii, followed by polyploidization and domestication. We studied whether the strong selection during these evolutionary processes, leading to genetic bottlenecks, may have resulted in a loss of resistance in domesticated wheat. In addition, we investigated whether putative fluctuations in intensity of selection imposed on the host-pathogen interactions have resulted in a variation in susceptibility to WDV. To test our hypotheses we evaluated eighteen wild and domesticated wheat taxa, directly or indirectly involved in wheat evolution, for traits associated with WDV disease such as leaf chlorosis, different growth traits and WDV content. The plants were exposed to viruliferous leafhoppers (Psammotettix alienus) in a greenhouse trial and evaluated at two time points. We found three different plant response patterns: i) continuous reduction in growth over time, ii) weak response at an early stage of plant development but a much stronger response at a later stage, and iii) remission of symptoms over time. Variation in susceptibility may be explained by differences in the intensity of natural selection, shaping the coevolutionary interaction between WDV and the wild relatives. However, genetic bottlenecks during wheat evolution have not had a strong impact on WDV resistance. Further, this study indicates that the variation in susceptibility may be associated with the genome type and that the ancestor Ae. tauschii may be useful as genetic resource for the improvement of WDV resistance in wheat. PMID

Variation in susceptibility to Wheat dwarf virus among wild and domesticated wheat.

Directory of Open Access Journals (Sweden)

Jim Nygren

Full Text Available We investigated the variation in plant response in host-pathogen interactions between wild (Aegilops spp., Triticum spp. and domesticated wheat (Triticum spp. and Wheat dwarf virus (WDV. The distribution of WDV and its wild host species overlaps in Western Asia in the Fertile Crescent, suggesting a coevolutionary relationship. Bread wheat originates from a natural hybridization between wild emmer wheat (carrying the A and B genomes and the wild D genome donor Aegilops tauschii, followed by polyploidization and domestication. We studied whether the strong selection during these evolutionary processes, leading to genetic bottlenecks, may have resulted in a loss of resistance in domesticated wheat. In addition, we investigated whether putative fluctuations in intensity of selection imposed on the host-pathogen interactions have resulted in a variation in susceptibility to WDV. To test our hypotheses we evaluated eighteen wild and domesticated wheat taxa, directly or indirectly involved in wheat evolution, for traits associated with WDV disease such as leaf chlorosis, different growth traits and WDV content. The plants were exposed to viruliferous leafhoppers (Psammotettix alienus in a greenhouse trial and evaluated at two time points. We found three different plant response patterns: i continuous reduction in growth over time, ii weak response at an early stage of plant development but a much stronger response at a later stage, and iii remission of symptoms over time. Variation in susceptibility may be explained by differences in the intensity of natural selection, shaping the coevolutionary interaction between WDV and the wild relatives. However, genetic bottlenecks during wheat evolution have not had a strong impact on WDV resistance. Further, this study indicates that the variation in susceptibility may be associated with the genome type and that the ancestor Ae. tauschii may be useful as genetic resource for the improvement of WDV resistance in

Marvel-ous Dwarfs: Results from Four Heroically Large Simulated Volumes of Dwarf Galaxies

Science.gov (United States)

Munshi, Ferah; Brooks, Alyson; Weisz, Daniel; Bellovary, Jillian; Christensen, Charlotte

2018-01-01

We present results from high resolution, fully cosmological simulations of cosmic sheets that contain many dwarf galaxies. Together, they create the largest collection of simulated dwarf galaxies to date, with z=0 stellar masses comparable to the LMC or smaller. In total, we have simulated almost 100 luminous dwarf galaxies, forming a sample of simulated dwarfs which span a wide range of physical (stellar and halo mass) and evolutionary properties (merger history). We show how they can be calibrated against a wealth of observations of nearby galaxies including star formation histories, HI masses and kinematics, as well as stellar metallicities. We present preliminary results answering the following key questions: What is the slope of the stellar mass function at extremely low masses? Do halos with HI and no stars exist? What is the scatter in the stellar to halo mass relationship as a function of dwarf mass? What drives the scatter? With this large suite, we are beginning to statistically characterize dwarf galaxies and identify the types and numbers of outliers to expect.

From strange stars to strange dwarfs

International Nuclear Information System (INIS)

Glendenning, N.K.; Kettner, C.; Weber, F.

1995-01-01

We determine all possible equilibrium sequences of compact strange-matter stars with nuclear crusts, which range from massive strange stars to strange white dwarf endash like objects (strange dwarfs). The properties of such stars are compared with those of their nonstrange counterparts emdash neutron stars and ordinary white dwarfs. The main emphasis of this paper is on strange dwarfs, which we divide into two distinct categories. The first one consists of a core of strange matter enveloped within ordinary white dwarf matter. Such stars are hydrostatically stable with or without the strange core and are therefore referred to as open-quote open-quote trivial close-quote close-quote strange dwarfs. This is different for the second category which forms an entirely new class of dwarf stars that contain nuclear material up to 4x10 4 times denser than in ordinary white dwarfs of average mass, M∼0.6 M circle-dot , and still about 400 times denser than in the densest white dwarfs. The entire family of such dwarfs, denoted dense strange dwarfs, owes its hydrostatic stability to the strange core. A striking features of strange dwarfs is that the entire sequence from the maximum-mass strange star to the maximum-mass strange dwarf is stable to radial oscillations. The minimum-mass star is only conditionally stable, and the sequences on both sides are stable. Such a stable, continuous connection does not exist between ordinary white dwarfs and neutron stars, which are known to be separated by a broad range of unstable stars. We find an expansive range of very low mass (planetary-like) strange-matter stars (masses even below 10 -4 M circle-dot are possible) that arise as natural dark-matter candidates, which if abundant enough in our Galaxy, should be seen in the gravitational microlensing searches that are presently being performed. copyright 1995 The American Astronomical Society

Hubble Space Telescope Imaging and Spectral Analysis of Two Brown Dwarf Binaries at the L Dwarf/T Dwarf Transition

OpenAIRE

Burgasser, Adam J.; Gagliuffi, Daniella C. Bardalez; Gizis, John E.

2010-01-01

We present a detailed examination of the brown dwarf multiples 2MASS J08503593+1057156 and 2MASS J17281150+3948593, both suspected of harboring components that straddle the L dwarf/T dwarf transition. Resolved photometry from Hubble Space Telescope/NICMOS show opposite trends in the relative colors of the components, with the secondary of 2MASS J0850+1057 being redder than its primary, while that of 2MASS J1728+3948 is bluer. We determine near-infrared component types by matching combined-lig...

Brown dwarfs as dark galactic halos

International Nuclear Information System (INIS)

Adams, F.C.; Walker, T.P.

1990-01-01

The possibility that the dark matter in galactic halos can consist of brown dwarf stars is considered. The radiative signature for such halos consisting solely of brown dwarfs is calculated, and the allowed range of brown dwarf masses, the initial mass function (IMF), the stellar properties, and the density distribution of the galactic halo are discussed. The prediction emission from the halo is compared with existing observations. It is found that, for any IMF of brown dwarfs below the deuterium burning limit, brown dwarf halos are consistent with observations. Brown dwarf halos cannot, however, explain the recently observed near-IR background. It is shown that future satellite missions will either detect brown dwarf halos or place tight constraints on the allowed range of the IMF. 30 refs

Agronomic performances of three vetch species growing under different drought levels

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Sywar Haffani

2014-09-01

Full Text Available The current challenge of agriculture is to get the best yields while overcoming frequent water deficit conditions. The objective of this study was to compare performances of three vetch species (Vicia narbonensis L., V. sativa L., and V. villosa Roth subjected to water stress. Plants were sown in pots under rainout shelter and submitted to four water regimes: control (100% field capacity [FC], 80%, 60%, and 40% FC through 3 yr experiment. Results showed that V. narbonensis had the smallest declines in all the studied variables in response to water restriction but the highest water use efficiency (WUE and stress tolerance index (STI in both control and water-treated plants. This indicates the greater tolerance of this species to water constraint and its better water use. Vicia villosa was characterized by drastic declines in leaf area and DM yield (75% and 64%, respectively. It had also the smallest WUE and STI suggesting its low adaptation to water stress. Vicia sativa showed severe reductions in seed yield and yield components; accordingly, it was the most sensitive species in terms of seed yield. The three species implied avoidance strategies to cope with water stress. The different levels of drought tolerance explain the species ecological distribution in Tunisia.

Testing Gravity Using Dwarf Stars

OpenAIRE

Sakstein, Jeremy

2015-01-01

Generic scalar-tensor theories of gravity predict deviations from Newtonian physics inside astrophysical bodies. In this paper, we point out that low mass stellar objects, red and brown dwarf stars, are excellent probes of these theories. We calculate two important and potentially observable quantities: the radius of brown dwarfs and the minimum mass for hydrogen burning in red dwarfs. The brown dwarf radius can differ significantly from the GR prediction and upcoming surveys that probe the m...

The galactic population of white dwarfs

International Nuclear Information System (INIS)

Napiwotzki, Ralf

2009-01-01

The contribution of white dwarfs of the different Galactic populations to the stellar content of our Galaxy is only poorly known. Some authors claim a vast population of halo white dwarfs, which would be in accordance with some investigations of the early phases of Galaxy formation claiming a top-heavy initial- mass- function. Here, I present a model of the population of white dwarfs in the Milky Way based on observations of the local white dwarf sample and a standard model of Galactic structure. This model will be used to estimate the space densities of thin disc, thick disc and halo white dwarfs and their contribution to the baryonic mass budget of the Milky Way. One result of this investigation is that white dwarfs of the halo population contribute a large fraction of the Galactic white dwarf number count, but they are not responsible for the lion's share of stellar mass in the Milky Way. Another important result is the substantial contribution of the - often neglected - population of thick disc white dwarfs. Misclassification of thick disc white dwarfs is responsible for overestimates of the halo population in previous investigations.

Dwarfs in ancient Egypt.

Science.gov (United States)

Kozma, Chahira

2006-02-15

Ancient Egypt was one of the most advanced and productive civilizations in antiquity, spanning 3000 years before the "Christian" era. Ancient Egyptians built colossal temples and magnificent tombs to honor their gods and religious leaders. Their hieroglyphic language, system of organization, and recording of events give contemporary researchers insights into their daily activities. Based on the record left by their art, the ancient Egyptians documented the presence of dwarfs in almost every facet of life. Due to the hot dry climate and natural and artificial mummification, Egypt is a major source of information on achondroplasia in the old world. The remains of dwarfs are abundant and include complete and partial skeletons. Dwarfs were employed as personal attendants, animal tenders, jewelers, and entertainers. Several high-ranking dwarfs especially from the Old Kingdom (2700-2190 BCE) achieved important status and had lavish burial places close to the pyramids. Their costly tombs in the royal cemeteries and the inscriptions on their statutes indicate their high-ranking position in Egyptian society and their close relation to the king. Some of them were Seneb, Pereniankh, Khnumhotpe, and Djeder. There were at least two dwarf gods, Ptah and Bes. The god Ptah was associated with regeneration and rejuvenation. The god Bes was a protector of sexuality, childbirth, women, and children. He was a favored deity particularly during the Greco-Roman period. His temple was recently excavated in the Baharia oasis in the middle of Egypt. The burial sites and artistic sources provide glimpses of the positions of dwarfs in daily life in ancient Egypt. Dwarfs were accepted in ancient Egypt; their recorded daily activities suggest assimilation into daily life, and their disorder was not shown as a physical handicap. Wisdom writings and moral teachings in ancient Egypt commanded respect for dwarfs and other individuals with disabilities. Copyright (c) 2005 Wiley-Liss, Inc.

THE LINK BETWEEN PLANETARY SYSTEMS, DUSTY WHITE DWARFS, AND METAL-POLLUTED WHITE DWARFS

International Nuclear Information System (INIS)

Debes, John H.; Walsh, Kevin J.; Stark, Christopher

2012-01-01

It has long been suspected that metal-polluted white dwarfs (types DAZ, DBZ, and DZ) and white dwarfs with dusty disks possess planetary systems, but a specific physical mechanism by which planetesimals are perturbed close to a white dwarf has not yet been fully posited. In this paper, we demonstrate that mass loss from a central star during post-main-sequence evolution can sweep planetesimals into interior mean motion resonances with a single giant planet. These planetesimals are slowly removed through chaotic excursions of eccentricity that in time create radial orbits capable of tidally disrupting the planetesimal. Numerical N-body simulations of the solar system show that a sufficient number of planetesimals are perturbed to explain white dwarfs with both dust and metal pollution, provided other white dwarfs have more massive relic asteroid belts. Our scenario requires only one Jupiter-sized planet and a sufficient number of asteroids near its 2:1 interior mean motion resonance. Finally, we show that once a planetesimal is perturbed into a tidal crossing orbit, it will become disrupted after the first pass of the white dwarf, where a highly eccentric stream of debris forms the main reservoir for dust-producing collisions. These simulations, in concert with observations of white dwarfs, place interesting limits on the frequency of planetary systems around main-sequence stars, the frequency of planetesimal belts, and the probability that dust may obscure future terrestrial planet finding missions.

Search for brown dwarfs and late M dwarfs in the Hyades and the Pleiades

International Nuclear Information System (INIS)

Zuckerman, B.; Becklin, E.E.; Hawaii Univ., Honolulu)

1987-01-01

The J and K colors of 14 white dwarfs that are believed to be single stars and members of either the Hyades or Pleiades clusters or the Hyades supercluster were measured, and no indication of any excess 2.2 micron (K) emission above that expected from the white dwarf was found. Based on recently published theoretical cooling curves for brown dwarfs, the existence of any cool companion stars, with masses greater than approximately 0.03 solar mass within a radius of 6 arcsec of eight white dwarfs in the Hyades cluster and greater than approximately 0.015 solar mass toward the single white dwarf in the Pleiades, is ruled out. This latter limit, only 15 Jupiter masses, is probably the lowest that has yet been established for any star by purely infrared techniques. 21 references

Influence of Conservation Tillage on some Soil Physical Properties and Crop Yield in Vetch-Wheat Rotation in Dryland Cold Region

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I Eskandari

2017-10-01

Full Text Available Introduction Winter wheat is an important, well-adapted grain crop under dryland condition of the northwest of Iran. Soil water is the most limiting resource for crop growth in dryland areas. Therefore, farmers need to use crop residues and minimum tillage to control the soil erosion and effectively store and to use the limited precipitation received for crop production. Crop rotation and tillage system could affect crop yield due to their effects on water conservation and soil chemical and physical properties. Galantini et al., (2000 studied the effect of crop rotation on wheat productivity in the Pampean semi-arid region of Argentina and found that a wheat–vetch (Vicia sativa L. rotation resulted in higher yield and protein content, and greater yield components than the other rotations.Payne et al. (2000 stated that where precipitation amount is marginal (400 mm, dry field pea offers a potential alternative to summer fallowing. The purpose of this study was to identify the optimal tillage system for increasing crop productivity in a vetch–wheat rotation in dryland farming of the northwest of Iran. Materials and Methods The field experiment was carried out from 2010 to 2014 at the Dryland Agricultural Research Station (latitude37° 12´N; longitude 46◦20´E; 1730 m a.s.l., 25 km east of Maragheh, East Azerbaijan Province, Iran. The long-term (10 years average precipitation, temperature and relative humidity of the station are 336.5 mm, 9.4 ◦C and 47.5%, respectively. The soil (Fine Mixed, Mesic, Vertic Calcixerepts, USDA system; Calcisols, FAO system at the study site had a clay loam texture in the 0–15 cm surface layer and a clay texture in the 15–80 cm depth. This study was conducted in vetch (Vicia pannonica- wheat (Triticum aestivum L. rotation. The experiment was arranged in a randomized complete block design with four replications. The tillage treatments consisted of (1 conventional tillage: moldboard plowing followed by one

The Weeds Response to the Winter Vetch (Vicia villosa and Chicklingpea (Lathyrus sativus Cover Crops under Different Tillage Methods in Corn Fields

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Javad Hamzei

2017-01-01

Full Text Available Introduction: Using cover crops in conservation tillage systems offers many advantages, one of which is weed control through physical and chemical interferences. Most of the benefits of cover crops are well known. They prevent form wind and water erosions, conserve soil moisture by reducing evaporation and increasing infiltration, increase the content of organic matter, increase fertility by recycling nutrients, add nitrogen if they are legumes, and improve soil structure. Proper cover crops can also suppress weed growth by allelopathic activities and light interference. They impact on environmental quality through the protection of surface water and groundwater, as well as eliminating the need for using preemergence herbicides. Either increase or decreases have been reported for crop yields when the crop residues remain on soil surface. No-till system has been reported to increase the presence of certain difficult to control weeds. Therefore, the aim of this study was to investigate the effect of tillage systems and cover crops on weed control and corn yield. Materials and Methods: Experiment was carried out as split plot based on randomized complete block design with three replications at the Bu-Ali Sina University in growing season of 2011. Tillage with moldboard, tillage with chisel (minimum tillage, and no tillage were considered as main plots and two cover crops, winter vetch and chicklingpea, chemical weed control and weed-infest treatment (control were considered as sub-plots. Cover crops were cultivated in late March 2011. In early June 2011, cover crops were harvested and were spread over the soil surface. The Plot size was 22.50 m-2. Five rows were in each plot with 75 cm intervals among rows and 18 cm among seedlings. 2 square were picked in the three central rows of each plot in order to determine the yield and yield components. From each plot three quadrants (1×1 mrandomly were picked and weeds and cover crops was separated. All

Binary Star Orbits. V. The Nearby White Dwarf/Red Dwarf Pair 40 Eri BC

Science.gov (United States)

Mason, Brian D.; Hartkopf, William I.; Miles, Korie N.

2017-11-01

A new relative orbit solution with new dynamical masses is determined for the nearby white dwarf-red dwarf pair 40 Eri BC. The period is 230.09 ± 0.68 years. It is predicted to close slowly over the next half-century, getting as close as 1.″32 in early 2066. We determine masses of 0.575 ± 0.018 {{ M }}⊙ for the white dwarf and 0.2041 ± 0.0064 {{ M }}⊙ for the red dwarf companion. The inconsistency of the masses determined by gravitational redshift and dynamical techniques, due to a premature orbit calculation, no longer exists.

Productivity of lactating cows fed on a diet of haylage from a vetch pea-oat mixture with the introduction of new biological preservative

OpenAIRE

P. I. Baryshnikov; V. N. Khaustov; S. V. Burtseva; R. V. Nekrasov; M. G. Chabaev; A. А. Zelenchikova; D. A. Durnikin

2016-01-01

The effect of a new biological preservative representing a mix of lyophilized Lactobacillus plantarum VKPM V-4173, Lactococcus lactis subsp. lactis VKPM V-2092 and Propionibacterium acidipropionici VKPMV-5723 strains (40 : 40 : 20) on the quality of haylage prepared from a mix of vetch, oats, and pea has been studied. The total bacteria content in the preservative was 1·1011 CFU/g. Five different variants of conservation of alfalfa haylage prepared at the budding stage were evaluated under la...

The ultracool-field dwarf luminosity-function and space density from the Canada-France Brown Dwarf Survey

Science.gov (United States)

Reylé, C.; Delorme, P.; Willott, C. J.; Albert, L.; Delfosse, X.; Forveille, T.; Artigau, E.; Malo, L.; Hill, G. J.; Doyon, R.

2010-11-01

Context. Thanks to recent and ongoing large scale surveys, hundreds of brown dwarfs have been discovered in the last decade. The Canada-France Brown Dwarf Survey is a wide-field survey for cool brown dwarfs conducted with the MegaCam camera on the Canada-France-Hawaii Telescope. Aims: Our objectives are to find ultracool brown dwarfs and to constrain the field brown-dwarf luminosity function and the mass function from a large and homogeneous sample of L and T dwarfs. Methods: We identify candidates in CFHT/MegaCam i' and z' images and follow them up with pointed near infrared (NIR) imaging on several telescopes. Halfway through our survey we found ~50 T dwarfs and ~170 L or ultra cool M dwarfs drawn from a larger sample of 1400 candidates with typical ultracool dwarfs i'-z' colours, found in 780 square degrees. Results: We have currently completed the NIR follow-up on a large part of the survey for all candidates from mid-L dwarfs down to the latest T dwarfs known with utracool dwarfs' colours. This allows us to draw on a complete and well defined sample of 102 ultracool dwarfs to investigate the luminosity function and space density of field dwarfs. Conclusions: We found the density of late L5 to T0 dwarfs to be 2.0+0.8-0.7 × 10-3 objects pc-3, the density of T0.5 to T5.5 dwarfs to be 1.4+0.3-0.2 × 10-3 objects pc-3, and the density of T6 to T8 dwarfs to be 5.3+3.1-2.2 × 10-3 objects pc-3. We found that these results agree better with a flat substellar mass function. Three latest dwarfs at the boundary between T and Y dwarfs give the high density 8.3+9.0-5.1 × 10-3 objects pc-3. Although the uncertainties are very large this suggests that many brown dwarfs should be found in this late spectral type range, as expected from the cooling of brown dwarfs, whatever their mass, down to very low temperature. Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT), which is operated by

MicroRNAs responding to southern rice black-streaked dwarf virus infection and their target genes associated with symptom development in rice.

Science.gov (United States)

Xu, Donglin; Mou, Guiping; Wang, Kang; Zhou, Guohui

2014-09-22

Southern rice black-streaked dwarf virus (SRBSDV) is a recently emerged rice virus that has spread across Asia. This devastating virus causes rice plants to produce a variety of symptoms during different growth stages. MicroRNAs (miRNAs) comprise a large group of 21-24-nt RNA molecules that are important regulators of plant development processes and stress responses. In this study, we used microarray profiling to investigate rice miRNAs responding to SRBSDV infection at 3, 9, 15, and 20 days post-inoculation (dpi). Expression levels of 56 miRNAs were altered in SRBSDV-infected rice plants, with these changes classified into eight different regulation patterns according to their temporal expression dynamics. Fourteen miRNAs belonging to six families (miR164, R396, R530, R1846, R1858, and R2097) were significantly regulated at 20 dpi. We used RT-qPCR to search for expression level correlations between members of these families and their putative targets at 3, 9, and 15 dpi. Some members of the miR164, R396, R530, and R1846 families were found to be positively or negatively correlated with their respective targets during 3-15 days after SRBSDV infection, whereas in more cases the rice miRNAs were not in correlation with their targets along the post-inoculation period, suggesting that some additional factors may be involved in rice miRNA-target interactions. The reported functions of rice genes targeted by the miR164, R396, R530, R1846, and R1858 families indicated that these genes are associated with symptom development. These results provide insights into miRNA-mediated SRBSDV-rice interactions. Copyright © 2014 Elsevier B.V. All rights reserved.

Effect of silage from ryegrass intercropped with winter or common vetch for grazing dairy cows in small-scale dairy systems in Mexico.

Science.gov (United States)

Hernández-Ortega, Martha; Heredia-Nava, Darwin; Espinoza-Ortega, Angelica; Sánchez-Vera, Ernesto; Arriaga-Jordán, Carlos M

2011-06-01

The objective was to determine the effect of including silages of annual ryegrass (Lolium multiflorum) intercropped with winter vetch (Vicia villosa) (ARG-VV) or with common vetch (Vicia sativa) (ARG-VS) compared with maize silage (MS) on milk yield and milk composition of dairy cows grazing cultivated perennial ryegrass-white clover pastures with supplemented concentrate during the dry season. Six Holstein dairy cows with a mean yield of 19.0 kg/cow/day at the beginning of the experiment were randomly assigned to a 3 × 3 repeated Latin square. Treatments were: 8 h/day intensive grazing, 3.6 kg of dry matter (DM) per cow per day of concentrate plus MS, and ARG-VV or ARG-VS ad libitum at a stocking rate of 3.0 cows/ha for three experimental periods of 3 weeks each. Milk yield (MY) and milk composition, live weight and body condition score as well as silage and concentrate intakes were recorded during the third week of each experimental period, and pasture intake was estimated indirectly from utilised metabolisable energy. Economic analysis was obtained by preparing partial budgets. There were no statistical differences (P > 0.10) in MY, milk fat or protein content nor for live weight, but there was significant difference (P dairy production systems in the dry season as it is comparable to MS in animal performance and slightly better in economic terms.

Rice Dwarf Virus P2 Protein Hijacks Auxin Signaling by Directly Targeting the Rice OsIAA10 Protein, Enhancing Viral Infection and Disease Development.

Directory of Open Access Journals (Sweden)

Lian Jin

2016-09-01

Full Text Available The phytohormone auxin plays critical roles in regulating myriads of plant growth and developmental processes. Microbe infection can disturb auxin signaling resulting in defects in these processes, but the underlying mechanisms are poorly understood. Auxin signaling begins with perception of auxin by a transient co-receptor complex consisting of an F-box transport inhibitor response 1/auxin signaling F-box (TIR1/AFB protein and an auxin/indole-3-acetic acid (Aux/IAA protein. Auxin binding to the co-receptor triggers ubiquitination and 26S proteasome degradation of the Aux/IAA proteins, leading to subsequent events, including expression of auxin-responsive genes. Here we report that Rice dwarf virus (RDV, a devastating pathogen of rice, causes disease symptoms including dwarfing, increased tiller number and short crown roots in infected rice as a result of reduced sensitivity to auxin signaling. The RDV capsid protein P2 binds OsIAA10, blocking the interaction between OsIAA10 and OsTIR1 and inhibiting 26S proteasome-mediated OsIAA10 degradation. Transgenic rice plants overexpressing wild-type or a dominant-negative (degradation-resistant mutant of OsIAA10 phenocopy RDV symptoms are more susceptible to RDV infection; however, knockdown of OsIAA10 enhances the resistance of rice to RDV infection. Our findings reveal a previously unknown mechanism of viral protein reprogramming of a key step in auxin signaling initiation that enhances viral infection and pathogenesis.

The brown dwarf kinematics project

Science.gov (United States)

Faherty, Jackie K.

2010-10-01

Brown dwarfs are a recent addition to the plethora of objects studied in Astronomy. With theoretical masses between 13 and 75 MJupiter , they lack sustained stable Hydrogen burning so they never join the stellar main sequence. They have physical properties similar to both planets and low-mass stars so studies of their population inform on both. The distances and kinematics of brown dwarfs provide key statistical constraints on their ages, moving group membership, absolute brightnesses, evolutionary trends, and multiplicity. Yet, until my thesis, fundamental measurements of parallax and proper motion were made for only a relatively small fraction of the known population. To address this deficiency, I initiated the Brown Dwarf Kinematics (BDKP). Over the past four years I have re-imaged the majority of spectroscopically confirmed field brown dwarfs (or ultracool dwarfs---UCDs) and created the largest proper motion catalog for ultracool dwarfs to date. Using new astrometric information I examined population characteristics such as ages calculated from velocity dispersions and correlations between kinematics and colors. Using proper motions, I identified several new wide co-moving companions and investigated binding energy (and hence formation) limitations as well as the frequency of hierarchical companions. Concurrently over the past four years I have been conducting a parallax survey of 84 UCDs including those showing spectral signatures of youth, metal-poor brown dwarfs, and those within 20 pc of the Sun. Using absolute magnitude relations in J,H, and K, I identified overluminous binary candidates and investigated known flux-reversal binaries. Using current evolutionary models, I compared the MK vs J-K color magnitude diagram to model predictions and found that the low-surface gravity dwarfs are significantly red-ward and underluminous of predictions and a handful of late-type T dwarfs may require thicker clouds to account for their scatter.

Relating N2O emissions from energy crops to the avoided fossil fuel-derived CO2 – a study on bioethanol and biogas produced from organically managed maize, rye, vetch and grass-clover

DEFF Research Database (Denmark)

Carter, Mette Sustmann; Hauggard-Nielsen, Henrik; Thomsen, Sune Tjalfe

2010-01-01

‐derived CO2, where the N2O emission has been subtracted. This value does not account for farm machinery CO2 emissions and fuel consumption during biofuel production. We obtained the greatest net reduction in greenhouse gas emissions by co‐production of bioethanol and biogas or by biogas alone produced from...... fuel‐derived CO2, which is obtained when energy crops are used for biofuel production. The analysis includes five organically managed crops (viz. maize, rye, rye‐vetch, vetch and grass‐clover) and three scenarios for conversion of biomass to biofuel. The scenarios are 1) bioethanol production, 2......) biogas production and 3) co‐production of bioethanol and biogas, where the energy crops are first used for bioethanol fermentation and subsequently the residues from this process are utilized for biogas production. The net reduction in greenhouse gas missions is calculated as the avoided fossil fuel...

White dwarfs - the once and future suns

International Nuclear Information System (INIS)

Trimble, V.

1986-01-01

The history and properties of white dwarfs (Bessel's conclusion that Sirius and Procyon have invisible companions, Clark's discovery of Sirius B, Adams and Russell's study of white dwarf spectra, Chandrasekhar's explanation of white dwarf structure by equations incorporating quantum mechanics and relativity) are treated. Formation of white dwarfs, degeneracy, binary white dwarfs (and novae and supernovae) are explained. A mystery nearly 50 years old regarding the spectrum of the star Greenwich +70 degrees-8247 has been solved: it involves a stationary line phenomenon and a magnetic field of 300-500 million gauss. Processes being studied in white dwarfs and white dwarf models include gravitational settling, accretion, dredge-up, radiation pressure, and diffusive hydrogen burning

WHITE DWARF-RED DWARF SYSTEMS RESOLVED WITH THE HUBBLE SPACE TELESCOPE. II. FULL SNAPSHOT SURVEY RESULTS

International Nuclear Information System (INIS)

Farihi, J.; Hoard, D. W.; Wachter, S.

2010-01-01

Results are presented for a Hubble Space Telescope Advanced Camera for Surveys high-resolution imaging campaign of 90 white dwarfs with known or suspected low-mass stellar and substellar companions. Of the 72 targets that remain candidate and confirmed white dwarfs with near-infrared excess, 43 are spatially resolved into two or more components, and a total of 12 systems are potentially triples. For 68 systems where a comparison is possible, 50% have significant photometric distance mismatches between their white dwarf and M dwarf components, suggesting that white dwarf parameters derived spectroscopically are often biased due to the cool companion. Interestingly, 9 of the 30 binaries known to have emission lines are found to be visual pairs and hence widely separated, indicating an intrinsically active cool star and not irradiation from the white dwarf. There is a possible, slight deficit of earlier spectral types (bluer colors) among the spatially unresolved companions, exactly the opposite of expectations if significant mass is transferred to the companion during the common envelope phase. Using the best available distance estimates, the low-mass companions to white dwarfs exhibit a bimodal distribution in projected separation. This result supports the hypothesis that during the giant phases of the white dwarf progenitor, any unevolved companions either migrate inward to short periods of hours to days, or outward to periods of hundreds to thousands of years. No intermediate projected separations of a few to several AU are found among these pairs. However, a few double M dwarfs (within triples) are spatially resolved in this range, empirically demonstrating that such separations were readily detectable among the binaries with white dwarfs. A straightforward and testable prediction emerges: all spatially unresolved, low-mass stellar and substellar companions to white dwarfs should be in short-period orbits. This result has implications for substellar companion and

Formation of dwarf ellipticals and dwarf irregular galaxies by interaction of giant galaxies under environmental influence

OpenAIRE

Chattopadhyay, Tanuka; Debsarma, Suma; Karmakar, Pradip; Davoust, Emmanuel

2014-01-01

A model is proposed for the formation of gas-rich dwarf irregular galaxies and gas-poor, rotating dwarf elliptical galaxies following the interaction between two giant galaxies as a function of space density. The formation of dwarf galaxies is considered to depend on a random variable, the tidal index theta, an environmental parameter defined by Karachentsev et al. (2004), such that for theta less than zero, the formation of dwarf irregular galaxy is assured whereas for theta greater than zer...

Asteroseismology of White Dwarf Stars

Science.gov (United States)

Hansen, Carl J.

1997-01-01

The primary purpose of this investigation has been to study various aspects of multimode pulsations in variable white dwarfs. In particular, nonlinear interactions among pulsation modes in white dwarfs (and, to some extent, in other variable stars), analysis of recent observations where such interactions are important, and preliminary work on the effects of crystallization in cool white dwarfs are reported.

SDSS DR7 WHITE DWARF CATALOG

Energy Technology Data Exchange (ETDEWEB)

Kleinman, S. J.; Nitta, A. [Gemini Observatory, 670 North A' ohoku Place, Hilo, HI 96720 (United States); Kepler, S. O.; Pelisoli, Ingrid; Pecanha, Viviane; Costa, J. E. S. [Instituto de Fisica, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS (Brazil); Koester, D. [Institut fuer Theoretische Physik und Astrophysik, Universitaet Kiel, D-24098 Kiel (Germany); Krzesinski, J. [Mt. Suhora Observatory, Pedagogical University of Cracow, ul. Podchorazych 2, 30-084 Cracow (Poland); Dufour, P.; Lachapelle, F.-R.; Bergeron, P. [Departement de Physique, Universite de Montreal, C. P. 6128, Succ. Centre-Ville, Montreal, Quebec H3C 3J7 (Canada); Yip, Ching-Wa [Department of Physics and Astronomy, The Johns Hopkins University, 3701 San Martin Drive, Baltimore, MD 21218 (United States); Harris, Hugh C. [United States Naval Observatory, Flagstaff Station, 10391 West Naval Observatory Road, Flagstaff, AZ 86001-8521 (United States); Eisenstein, Daniel J. [Harvard Smithsonian Center for Astrophysics, 60 Garden Street, MS 20, Cambridge, MA 02138 (United States); Althaus, L.; Corsico, A., E-mail: hch@nofs.navy.mil [Facultad de Ciencias Astronomicas y Geofisicas, Paseo del Bosque S/N, (1900) La Plata (Argentina)

2013-01-15

We present a new catalog of spectroscopically confirmed white dwarf stars from the Sloan Digital Sky Survey (SDSS) Data Release 7 spectroscopic catalog. We find 20,407 white dwarf spectra, representing 19,712 stars, and provide atmospheric model fits to 14,120 DA and 1011 DB white dwarf spectra from 12,843 and 923 stars, respectively. These numbers represent more than a factor of two increase in the total number of white dwarf stars from the previous SDSS white dwarf catalogs based on DR4 data. Our distribution of subtypes varies from previous catalogs due to our more conservative, manual classifications of each star in our catalog, supplementing our automatic fits. In particular, we find a large number of magnetic white dwarf stars whose small Zeeman splittings mimic increased Stark broadening that would otherwise result in an overestimated log g if fit as a non-magnetic white dwarf. We calculate mean DA and DB masses for our clean, non-magnetic sample and find the DB mean mass is statistically larger than that for the DAs.

The late-M dwarfs

International Nuclear Information System (INIS)

Bessell, M.S.

1991-01-01

Far-red spectra and VRIJHK photometry have been obtained for a sample of late-M dwarfs selected on the basis of large reduced red magnitudes from the LHS Catalog. Half of the stars in the three faintest 1 mag bins are late-M stars, the other red stars are metallic-hydride subdwarfs. Relations between various colors for the late-M dwarfs are investigated. Of all the colors I - K most reliably correlates with spectral type. FeH bands near 9900 A are clearly seen in the spectra of all dwarf stars later than M5. Two stars cooler than VB10, and similar in temperature to LHS2924 have been identified; both have H-alpha in emission and appear variable in magnitude and R - I color; one is a flare star. The other stars are of earlier spectral type and resemble W359 and VB8. The observed MI, I - K main sequence is in good agreement with the IG theoretical main sequence of Stringfellow, and the faintest stars could be about 0.09 solar mass red dwarfs or lower mass brown dwarfs. 65 refs

Understanding Brown Dwarf Variability

Science.gov (United States)

Marley, Mark S.

2013-01-01

Surveys of brown dwarf variability continue to find that roughly half of all brown dwarfs are variable. While variability is observed amongst all types of brown dwarfs, amplitudes are typically greatest for L-T transition objects. In my talk I will discuss the possible physical mechanisms that are responsible for the observed variability. I will particularly focus on comparing and contrasting the effects of changes in atmospheric thermal profile and cloud opacity. The two different mechanisms will produce different variability signatures and I will discuss the extent to which the current datasets constrain both mechanisms. By combining constraints from studies of variability with existing spectral and photometric datasets we can begin to construct and test self-consistent models of brown dwarf atmospheres. These models not only aid in the interpretation of existing objects but also inform studies of directly imaged giant planets.

Evolution models of helium white dwarf-main-sequence star merger remnants: the mass distribution of single low-mass white dwarfs

Science.gov (United States)

Zhang, Xianfei; Hall, Philip D.; Jeffery, C. Simon; Bi, Shaolan

2018-02-01

It is not known how single white dwarfs with masses less than 0.5Msolar -- low-mass white dwarfs -- are formed. One way in which such a white dwarf might be formed is after the merger of a helium-core white dwarf with a main-sequence star that produces a red giant branch star and fails to ignite helium. We use a stellar-evolution code to compute models of the remnants of these mergers and find a relation between the pre-merger masses and the final white dwarf mass. Combining our results with a model population, we predict that the mass distribution of single low-mass white dwarfs formed through this channel spans the range 0.37 to 0.5Msolar and peaks between 0.45 and 0.46Msolar. Helium white dwarf--main-sequence star mergers can also lead to the formation of single helium white dwarfs with masses up to 0.51Msolar. In our model the Galactic formation rate of single low-mass white dwarfs through this channel is about 8.7X10^-3yr^-1. Comparing our models with observations, we find that the majority of single low-mass white dwarfs (<0.5Msolar) are formed from helium white dwarf--main-sequence star mergers, at a rate which is about $2$ per cent of the total white dwarf formation rate.

Complete genome sequence of a divergent strain of lettuce chlorosis virus from Periwinkle in China

Science.gov (United States)

A novel strain of Lettuce chlorosis virus (LCV) was identified from periwinkle in China (PW) with foliar interveinal chlorosis and plant dwarfing. Complete nucleotide (nt) sequences of genomic RNA1 and RNA2 of the virus are 8,602 nt and 8,456 nt, respectively. The genomic organization of LCV-PW rese...

EROS 2 proper motion survey a field brown dwarf and an L dwarf companion to LHS 102

CERN Document Server

Goldman, B; Forveille, T; Afonso, C; Alard, C; Albert, J N; Andersen, J; Ansari, R; Aubourg, E; Bareyre, P; Bauer, F; Beaulieu, J P; Borsenberger, J; Bouquet, A; Char, S; Charlot, X; Couchot, F; Coutures, C; Derue, F; Ferlet, R; Fouqué, P; Glicenstein, J F; Gould, A; Graff, D S; Gros, M H; Haïssinski, J; Hamilton, J C; Hardin, D P; De Kat, J; Kim, A; Lasserre, T; Lesquoy, E; Loup, C; Magneville, C; Mansoux, B; Marquette, J B; Martín, E L; Maurice, E; Milshtein, A I; Moniez, M; Palanque-Delabrouille, Nathalie; Perdereau, O; Prévôt, L; Regnault, N; Rich, J; Spiro, Michel; Vidal-Madjar, A; Virgoux, L; Zylberajch, S

1999-01-01

We report the discovery of two L dwarfs (the new spectral class defined for dwarfs cooler than the M type) in a two-epoch CCD proper motion survey of 413 square degrees, complemented by infrared photometry from DENIS. One of them has a strong lithium line and is therefore a brown dwarf. The other is a common proper motion companion to the mid-M dwarf LHS 102 (GJ 1001), which has a well determined trigonometric parallax. LHS 102B is thus the coolest L dwarf of known distance and luminosity. Its infrared absolute photometry are very well reproduced by the Allard et al DUSTY models.

Mild and severe cereal yellow dwarf viruses differ in silencing suppressor efficiency of the P0 protein.

Science.gov (United States)

Almasi, Reza; Miller, W Allen; Ziegler-Graff, Véronique

2015-10-02

Viral pathogenicity has often been correlated to the expression of the viral encoded-RNA silencing suppressor protein (SSP). The silencing suppressor activity of the P0 protein encoded by cereal yellow dwarf virus-RPV (CYDV-RPV) and -RPS (CYDV-RPS), two poleroviruses differing in their symptomatology was investigated. CYDV-RPV displays milder symptoms in oat and wheat whereas CYDV-RPS is responsible for more severe disease. We showed that both P0 proteins (P0(CY-RPV) and P0(CY-RPS)) were able to suppress local RNA silencing induced by either sense or inverted repeat transgenes in an Agrobacterium tumefaciens-mediated expression assay in Nicotiana benthamiana. P0(CY-RPS) displayed slightly higher activity. Systemic spread of the silencing signal was not impaired. Analysis of short-interfering RNA (siRNA) abundance revealed that accumulation of primary siRNA was not affected, but secondary siRNA levels were reduced by both CYDV P0 proteins, suggesting that they act downstream of siRNA production. Correlated with this finding we showed that both P0 proteins partially destabilized ARGONAUTE1. Finally both P0(CY-RPV) and P0(CY-RPS) interacted in yeast cells with ASK2, a component of an E3-ubiquitin ligase, with distinct affinities. Copyright © 2015 Elsevier B.V. All rights reserved.

Infrared photometry of cool white dwarfs

International Nuclear Information System (INIS)

Wickramasinghe, D.T.; Allen, D.A.; Bessell, M.S.

1982-01-01

The results are presented of a search for the effects of pressure induced H 2 dipole opacity on the infrared JHK magnitudes of cool white dwarfs. LHS 1126 is found to be a very cool (Tsub(e) approximately 4250 K) DC white dwarf with a H rich atmospheric composition dominated by H 2 dipole opacity in the infrared. JHK photometry also favours a H rich atmospheric composition for the DK white dwarfs LP 658-2 and W 489. The surprisingly high proportion of hydrogen rich white dwarfs in the sample appears to suggest that the mechanism which inhibits the accretion of hydrogen in the hotter helium stars becomes less effective at low (Tsub(e) approximately 3 + ion in cool hydrogen rich white dwarf atmospheres is pointed out and it is suggested that the opacity due to this ion may be responsible for the blanketing observed in the U and B magnitudes of some cool white dwarfs. (author)

The Hunt for Missing Dwarf Galaxies

Science.gov (United States)

Kohler, Susanna

2015-11-01

Theories of galaxy formation and evolution predict that there should be significantly more dwarf galaxies than have been observed. Are our theories wrong? Or are dwarf galaxies just difficult to detect? Recent results from a survey of a galaxy cluster 62 million light-years away suggest there may be lots of undiscovered dwarf galaxies hiding throughout the universe!Hiding in FaintnessThe missing dwarf problem has had hints of a resolution with the recent discovery of Ultra-Diffuse Galaxies (UDGs) in the Coma and Virgo galaxy clusters. UDGs have low masses and large radii, resulting in a very low surface brightness that makes them extremely difficult to detect. If many dwarfs are UDGs, this could well explain why weve been missing them!But the Coma and Virgo galaxy clusters are similar in that theyre both very massive. Are there UDGs in other galaxy clusters as well? To answer this question, an international team of scientists is running the Next Generation Fornax Survey (NGFS), a survey searching for faint dwarf galaxies in the central 30 square degrees of the Fornax galaxy cluster.The NGFS uses near-UV and optical observations from the Dark Energy Camera mounted on the 4m Blanco Telescope in Chile. The survey is still underway, but in a recent publication led by Roberto P. Muoz (Institute of Astrophysics at the Pontifical Catholic University of Chile), the team has released an overview of the first results from only the central 3 square degrees of the NGFS field.Surprising DetectionGalaxy radii vs. their absolute i-band magnitudes, for the dwarfs found in NGFS as well as other stellar systems in the nearby universe. The NGFS dwarfs are similar to the ultra-diffuse dwarfs found in the Virgo and Coma clusters, but are several orders of magnitude fainter. [Muoz et al. 2015]In just this small central field, the team has found an astounding 284 low-surface-brightness dwarf galaxy candidates 158 of them previously undetected. At the bright end of this sample are dwarf

Characteristics of siRNAs derived from Southern rice black-streaked dwarf virus in infected rice and their potential role in host gene regulation.

Science.gov (United States)

Xu, Donglin; Zhou, Guohui

2017-02-10

Virus-derived siRNAs (vsiRNAs)-mediated RNA silencing plays important roles in interaction between plant viruses and their hosts. Southern rice black-streaked dwarf virus (SRBSDV) is a newly emerged devastating rice reovirus with ten dsRNA genomic segments. The characteristics of SRBSDV-derived siRNAs and their biological implications in SRBSDV-rice interaction remain unexplored. VsiRNAs profiling from SRBSDV-infected rice samples was done via small RNA deep sequencing. The putative rice targets of abundantly expressed vsiRNAs were bioinformatically predicted and subjected to functional annotation. Differential expression analysis of rice targets and RNA silencing components between infected and healthy samples was done using RT-qPCR. The vsiRNA was barely detectable at 14 days post infection (dpi) but abundantly present along with elevated expression level of the viral genome at 28 dpi. From the 28-dpi sample, 70,878 reads of 18 ~ 30-nt vsiRNAs were recognized (which mostly were 21-nt and 22-nt), covering 75 ~ 91% of the length of the ten genomic segments respectively. 86% of the vsiRNAs had a rice genes, including several types of host resistance or pathogenesis related genes encoding F-box/LRR proteins, receptor-like protein kinases, universal stress proteins, tobamovirus multiplication proteins, and RNA silencing components OsDCL2a and OsAGO17 respectively, some of which showed down regulation in infected plants in RT-qPCR. GO and KEGG classification showed that a majority of the predicted targets were related to cell parts and cellular processes and involved in carbohydrate metabolism, translation, and signal transduction. The silencing component genes OsDCL2a, OsDCL2b, OsDCL4, and OsAGO18 were down regulated, while OsAGO1d, OsAGO2, OsRDR1 and OsRDR6 were up regulated, significantly, upon SRBSDV infection. SRBSDV can regulate the expression of rice RNA silencing pathway components and the virus might compromise host defense and influence host

Lists of semi-dwarf cereal stocks

International Nuclear Information System (INIS)

1984-01-01

The lists are prepared in relation to the Co-ordinated Research Programme. At the first Research Co-ordination Meeting on evaluation of cereal semi-dwarf mutants for cross breeding, March 1981, programme participants were requested to list semi-dwarf mutants available at their institutes including also non-induced semi-dwarf stocks being used in cross-breeding programme for short stature. List-I is prepared from such lists provided by programme participants. Further it was requested to name breeders and institutes providing characteristics of the listed semi-dwarf stocks. List-II gives that information. In the List-I: Parents of semi-dwarf stocks derived from cross breeding, are shown in brackets. In column ''Culm length'', figures are in cm and those of parent cultivars are shown in brackets

Pulsations in white dwarf stars

OpenAIRE

Van Grootel, Valérie; Fontaine, Gilles; Brassard, Pierre; Dupret, Marc-Antoine

2017-01-01

I will present a description of the six distinct families of pulsating white dwarfs that are currently known. Pulsations are present at various stages of the evolution (from hot, pre-white dwarfs to cool white dwarfs), at various stellar masses, and for various atmospheric compositions. In all of them, a mechanism linked to opacity changes along the evolution drives the oscillations. The existence of these oscillations offers the opportunity to apply asteroseismology for constraining physics ...

White dwarfs in the WTS: Eclipsing binaries

Directory of Open Access Journals (Sweden)

Burleigh M.R.

2013-04-01

Full Text Available We have identified photometric white dwarf candidates in the WFCAM transit survey through a reduced proper motion versus colour approach. Box-fitting with parameters adjusted to detect the unique signature of a white dwarf + planet/brown dwarf transit/eclipse event was performed, as well as looking for variability due to the irradiation of the companions atmosphere by the white dwarf's high UV flux. We have also performed a simple sensitivity analysis in order to assess the ability of the survey to detect companions to white dwarfs via the transit method.

Habitability of planets around red dwarf stars.

Science.gov (United States)

Heath, M J; Doyle, L R; Joshi, M M; Haberle, R M

1999-08-01

Recent models indicate that relatively moderate climates could exist on Earth-sized planets in synchronous rotation around red dwarf stars. Investigation of the global water cycle, availability of photosynthetically active radiation in red dwarf sunlight, and the biological implications of stellar flares, which can be frequent for red dwarfs, suggests that higher plant habitability of red dwarf planets may be possible.

A systematic search for brown dwarfs orbiting nearby stars

International Nuclear Information System (INIS)

Henry, T.J.; Mccarthy, D.W. Jr.

1990-01-01

Survey data for brown dwarf and stellar companions relative to known M dwarf stars within 5 pc north of -30 deg are analyzed. A region 0.2 to 5 arcsec in radius around 27 stars at the IR H and K bands are examined using IR speckle interferometry. The frequency of binary versus single M dwarfs in the solar neighborhood is examined. The IR mass-magnitude relations and mass-luminosity-age relation are studied. The data reveal that there are 19 single M dwarfs, 8 M dwarf binaries, 1 M dwarf triple system, and 1 M dwarf in a triple system for M dwarfs within 5 pc north of -30 deg. Also of the 27 M dwarfs studied none was found to have a brown dwarf companion. 64 refs

The Metallicity of Void Dwarf Galaxies

Science.gov (United States)

Kreckel, K.; Croxall, K.; Groves, B.; van de Weygaert, R.; Pogge, R. W.

2015-01-01

The current ΛCDM cosmological model predicts that galaxy evolution proceeds more slowly in lower density environments, suggesting that voids are a prime location to search for relatively pristine galaxies that are representative of the building blocks of early massive galaxies. To test the assumption that void galaxies are more pristine, we compare the evolutionary properties of a sample of dwarf galaxies selected specifically to lie in voids with a sample of similar isolated dwarf galaxies in average density environments. We measure gas-phase oxygen abundances and gas fractions for eight dwarf galaxies (Mr > -16.2), carefully selected to reside within the lowest density environments of seven voids, and apply the same calibrations to existing samples of isolated dwarf galaxies. We find no significant difference between these void dwarf galaxies and the isolated dwarf galaxies, suggesting that dwarf galaxy chemical evolution proceeds independent of the large-scale environment. While this sample is too small to draw strong conclusions, it suggests that external gas accretion is playing a limited role in the chemical evolution of these systems, and that this evolution is instead dominated mainly by the internal secular processes that are linking the simultaneous growth and enrichment of these galaxies.

Evolution of White Dwarf Stars

OpenAIRE

L. G. Althaus

2001-01-01

This paper is aimed at presenting the main results we have obtained for the study of the evoution of white dwarf stars. The calculations are carried out by means of a detailed evolutionary code based on an updated physical description. In particular, we briefly discuss the results for the evolution of white dwarfs of different stellar masses and chemical composition, and the evolution of whit e dwarfs in the framework of a varying gravitational constant G scenario as well.

Calibrating Detailed Chemical Analysis of M dwarfs

Science.gov (United States)

Veyette, Mark; Muirhead, Philip Steven; Mann, Andrew; Brewer, John; Allard, France; Homeier, Derek

2018-01-01

The ability to perform detailed chemical analysis of Sun-like F-, G-, and K-type stars is a powerful tool with many applications including studying the chemical evolution of the Galaxy, assessing membership in stellar kinematic groups, and constraining planet formation theories. Unfortunately, complications in modeling cooler stellar atmospheres has hindered similar analysis of M-dwarf stars. Large surveys of FGK abundances play an important role in developing methods to measure the compositions of M dwarfs by providing benchmark FGK stars that have widely-separated M dwarf companions. These systems allow us to empirically calibrate metallicity-sensitive features in M dwarf spectra. However, current methods to measure metallicity in M dwarfs from moderate-resolution spectra are limited to measuring overall metallicity and largely rely on astrophysical abundance correlations in stellar populations. In this talk, I will discuss how large, homogeneous catalogs of precise FGK abundances are crucial to advancing chemical analysis of M dwarfs beyond overall metallicity to direct measurements of individual elemental abundances. I will present a new method to analyze high-resolution, NIR spectra of M dwarfs that employs an empirical calibration of synthetic M dwarf spectra to infer effective temperature, Fe abundance, and Ti abundance. This work is a step toward detailed chemical analysis of M dwarfs at a similar precision achieved for FGK stars.

Observations of Superwinds in Dwarf Galaxies

Science.gov (United States)

Marlowe, A. T.; Heckman, T. M.; Wyse, R.; Schommer, R.

1993-12-01

Dwarf galaxies are important in developing our understanding of the formation and evolution of galaxies, and of the structure in the universe. The concept of supernova-driven mass outflows is a vital ingredient in theories of the structure and evolution of dwarfs galaxies. We have begun a detailed multi-waveband search for outflows in starbursting dwarf galaxies, and have obtained Fabry-Perot images and Echelle spectra of 20 nearby actively-star-forming dwarf galaxies. In about half the sample, the Fabry-Perot Hα images show loops and filaments with sizes of one to a few kpc. The Echelle spectra taken through the loops and filaments show kinematics consistent with expanding bubble-like structures. We describe these data, and present seven dwarfs in our sample that have the strongest evidence of outflows.

Evidence for the Translocation of Gibberellin A_3 and Gibberellin-Like Substances in Grafts between Normal, Dwarf_1 and Dwarf_5 Seedlings of Zea mays L.

OpenAIRE

M., Katsumi; D.E., Foard; B.O., Phinney; Biology Department, International Christian University; Department of Botany and Plant Pathology, Purdue University; Department of Biology, University of California

1983-01-01

Approach grafts were made between the cut surfaces of mesocotyls from normal and dwarf seedlings of Zea mays L. (maize). The dwarfs were the non-allelic single gene gibberellin mutants, dwarf_1 and dwarf_5. The graft combinations were normal-normal, normal-dwarf_1, normal-dwarf_5, dwarf_1-dwarf_1, dwarf_5-dwarf_5, and dwarf_1-dwarf_5. The grafts were used to demonstrate the movement of gibberellin-like substances across the union. GA_3, added to one member of the graft, resulted in leaf-sheat...

PREFACE: 16th European White Dwarfs Workshop

Science.gov (United States)

Garcia-Berro, Enrique; Hernanz, Margarita; Isern, Jordi; Torres, Santiago

2009-07-01

The 16th European Workshop on White Dwarfs was held in Barcelona, Spain, from 30 June to 4 July 2008 at the premises of the UPC. Almost 120 participants from Europe (France, Germany, United Kingdom, Italy, and several others), America (USA, Canada, Argentina, Brazil, and Chile), and other continents (Australia, South Africa, . . . ) attended the workshop. Among these participants were the most relevant specialists in the field. The topics covered by the conference were: White dwarf structure and evolution Progenitors and Planetary Nebulae White dwarfs in binaries: cataclysmic variables, double degenerates and other binaries White dwarfs, dust disks and planetary systems Atmospheres, chemical composition, magnetic fields Variable white dwarfs White dwarfs in stellar clusters and the halo White Dwarfs as SNIa progenitors The programme included 54 talks, and 45 posters. The oral presentations were distributed into the following sessions: Luminosity function, mass function and populations White dwarf structure and evolution White dwarf ages White dwarf catalogs and surveys Central stars of planetary nebulae Supernovae progenitors White dwarfs in novae and CVs Physical processes in white dwarfs and magnetic white dwarfs Disks, dust and planets around white dwarfs Pulsating white dwarfs Additionally we had a special open session about Spitzer and white dwarfs. The Proceedings of the 16th European Workshop on White Dwarfs are representative of the current state-of-the-art of the research field and include new and exciting results. We acknowledge the very positive attitude of the attendants to the workshop, which stimulated very fruitful discussions that took place in all the sessions and after the official schedule. Also, the meeting allowed new collaborations tp start that will undoubtedly result in significant advances in the research field. We also acknowledge the willingness of the participants to deliver their contributions before the final deadline. We sincerely

Simultaneous Detection of Barley Virus Diseases in Korea

Directory of Open Access Journals (Sweden)

Bong-Choon Lee

2017-12-01

Full Text Available Barley mild mosaic virus (BaMMV, Barley yellow mosaic virus (BaYMV and Barley yellow dwarf virus (BYDV have been identified as an important causative agents for an economically important disease of winter barley in Korea. In this study, a multiplex reverse transcription polymerase chain reaction (mRT-PCR method was used for the simultaneous detection. Three sets of virus-specific primers targeted to the capsid protein coding genes of BaMMV, BaYMV and BYDV were used to amplify fragments that were 594 bp, 461 bp, and 290 bp, respectively. Several sets of primers for each target virus were evaluated for their sensitivity and specificity by multiplex RT-PCR. The optimum primer concentrations and RT-PCR conditions were determined for the multiplex RT-PCR. The mRT-PCR assay was found to be a better and rapid virus diagnostic tool of specific barley diseases and potential for investigating the epidemiology of these viral diseases.

SpeX Spectroscopy of Unresolved Very Low-Mass Binaries. I. Identification of Seventeen Candidate Binaries Straddling the L Dwarf/T Dwarf Transition

OpenAIRE

Burgasser, Adam J.; Cruz, Kelle L.; Cushing, Michael C.; Gelino, Christopher R.; Looper, Dagny L.; Faherty, Jacqueline K.; Kirkpatrick, J. Davy; Reid, I. Neill

2009-01-01

We report the identification of 17 candidate brown dwarf binaries whose components straddle the L dwarf/T dwarf transition. These sources were culled from a large near-infrared spectral sample of L and T dwarfs observed with the Infrared Telescope Facility SpeX spectrograph. Candidates were selected on the basis of spectral ratios which segregate known (resolved) L dwarf/T dwarf pairs from presumably single sources. Composite templates, constructed by combining 13581 pairs of absolute flux-ca...

Quantum liquid signatures in dwarf stars

Energy Technology Data Exchange (ETDEWEB)

Gabadadze, Gregory; Pirtskhalava, David, E-mail: gg32@nyu.edu, E-mail: dmp371@nyu.edu [Center for Cosmology and Particle Physics, Department of Physics, New York University, New York, NY 10003 (United States)

2009-05-15

We develop further the proposal of arXiv:0806.3692 that a new state of matter - charged condensate of spin-0 nuclei - may exist in helium-core dwarf stars. The charged condensate and its fluctuations are described by an effective field theory Lagrangian. The spectrum of bosonic fluctuations is gapped, while electrons, at temperatures of interest, give rise to gapless excitations near the Fermi surface. These properties determine the evolution of the dwarfs with condensed cores. In particular, we show that such dwarf stars would cool significantly faster than their crystallized counterparts. As a result, the luminosity function for the helium-core dwarfs will have a sharp drop-off after the condensation. It is tempting to interpret the recently discovered abrupt termination of a sequence of 24 helium-core dwarf candidates in NGC 6397 as a signature of the charged condensation.

Milky Way red dwarfs in the BoRG survey; galactic scale-height and the distribution of dwarf stars in WFC3 imaging

International Nuclear Information System (INIS)

Holwerda, B. W.; Bouwens, R.; Trenti, M.; Clarkson, W.; Sahu, K.; Bradley, L.; Stiavelli, M.; Pirzkal, N.; Ryan, R.; De Marchi, G.; Andersen, M.

2014-01-01

We present a tally of Milky Way late-type dwarf stars in 68 Wide Field Camera 3 (WFC3) pure-parallel fields (227 arcmin 2 ) from the Brightest of Reionizing Galaxies survey for high-redshift galaxies. Using spectroscopically identified M-dwarfs in two public surveys, the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey and the Early Release Science mosaics, we identify a morphological selection criterion using the half-light radius (r 50 ), a near-infrared J – H, G – J color region where M-dwarfs are found, and a V – J relation with M-dwarf subtype. We apply this morphological selection of stellar objects, color-color selection of M-dwarfs, and optical-near-infrared color subtyping to compile a catalog of 274 M-dwarfs belonging to the disk of the Milky Way with a limiting magnitude of m F125W < 24(AB). Based on the M-dwarf statistics, we conclude that (1) the previously identified north-south discrepancy in M-dwarf numbers persists in our sample; there are more M-dwarfs in the northern fields on average than in southern ones, (2) the Milky Way's single disk scale-height for M-dwarfs is 0.3-4 kpc, depending on subtype, (3) the scale-height depends on M-dwarf subtype with early types (M0-4) high scale-height (z 0 = 3-4 kpc) and later types M5 and above in the thin disk (z 0 = 0.3-0.5 kpc), (4) a second component is visible in the vertical distribution, with a different, much higher scale-height in the southern fields compared to the northern ones. We report the M-dwarf component of the Sagittarius stream in one of our fields with 11 confirmed M-dwarfs, seven of which are at the stream's distance. In addition to the M-dwarf catalog, we report the discovery of 1 T-dwarfs and 30 L-dwarfs from their near-infrared colors. The dwarf scale-height and the relative low incidence in our fields of L- and T-dwarfs in these fields makes it unlikely that these stars will be interlopers in great numbers in color-selected samples of high-redshift galaxies

Milky Way red dwarfs in the BoRG survey; galactic scale-height and the distribution of dwarf stars in WFC3 imaging

Energy Technology Data Exchange (ETDEWEB)

Holwerda, B. W.; Bouwens, R. [Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands); Trenti, M. [Kavli Institute for Cosmology and Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA (United Kingdom); Clarkson, W. [Department of Natural Sciences College of Arts, Sciences and Letters, University of Michigan-Dearborn 4901 Evergreen Road, Dearborn, MI 48128 (United States); Sahu, K.; Bradley, L.; Stiavelli, M.; Pirzkal, N.; Ryan, R. [Space Telescope Science Institute, Baltimore, MD 21218 (United States); De Marchi, G. [European Space Agency, ESA-ESTEC, Keplerlaan 1, 2200 AG Noordwijk (Netherlands); Andersen, M., E-mail: holwerda@strw.leidenuniv.nl [UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d' Astrophysique de Grenoble (IPAG) UMR 5274, F-38041 Grenoble (France)

2014-06-10

We present a tally of Milky Way late-type dwarf stars in 68 Wide Field Camera 3 (WFC3) pure-parallel fields (227 arcmin{sup 2}) from the Brightest of Reionizing Galaxies survey for high-redshift galaxies. Using spectroscopically identified M-dwarfs in two public surveys, the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey and the Early Release Science mosaics, we identify a morphological selection criterion using the half-light radius (r {sub 50}), a near-infrared J – H, G – J color region where M-dwarfs are found, and a V – J relation with M-dwarf subtype. We apply this morphological selection of stellar objects, color-color selection of M-dwarfs, and optical-near-infrared color subtyping to compile a catalog of 274 M-dwarfs belonging to the disk of the Milky Way with a limiting magnitude of m {sub F125W} < 24(AB). Based on the M-dwarf statistics, we conclude that (1) the previously identified north-south discrepancy in M-dwarf numbers persists in our sample; there are more M-dwarfs in the northern fields on average than in southern ones, (2) the Milky Way's single disk scale-height for M-dwarfs is 0.3-4 kpc, depending on subtype, (3) the scale-height depends on M-dwarf subtype with early types (M0-4) high scale-height (z {sub 0} = 3-4 kpc) and later types M5 and above in the thin disk (z {sub 0} = 0.3-0.5 kpc), (4) a second component is visible in the vertical distribution, with a different, much higher scale-height in the southern fields compared to the northern ones. We report the M-dwarf component of the Sagittarius stream in one of our fields with 11 confirmed M-dwarfs, seven of which are at the stream's distance. In addition to the M-dwarf catalog, we report the discovery of 1 T-dwarfs and 30 L-dwarfs from their near-infrared colors. The dwarf scale-height and the relative low incidence in our fields of L- and T-dwarfs in these fields makes it unlikely that these stars will be interlopers in great numbers in color-selected samples of

An overview of white dwarf stars

Directory of Open Access Journals (Sweden)

Charpinet S.

2013-03-01

Full Text Available We present a brief summary of what is currently known about white dwarf stars, with an emphasis on their evolutionary and internal properties. As is well known, white dwarfs represent the end products of stellar evolution for the vast majority of stars and, as such, bear the signatures of past events (such as mass loss, mixing phases, loss and redistribution of angular momentum, and thermonuclear burning that are of essential importance in the evolution of stars in general. In addition, white dwarf stars represent ideal testbeds for our understanding of matter under extreme conditions, and work on their constitutive physics (neutrino production rates, conductive and radiative opacities, interior liquid/solid equations of state, partially ionized and partially degenerate envelope equations of state, diffusion coefficients, line broadening mechanisms is still being actively pursued. Given a set of constitutive physics, cooling white dwarfs can be used advantageously as cosmochronometers. Moreover, the field has been blessed by the existence of four distinct families of pulsating white dwarfs, each mapping a different evolutionary phase, and this allows the application of the asteroseismological method to probe and test their internal structure and evolutionary state. We set the stage for the reviews that follow on cooling white dwarfs as cosmochronometers and physics laboratories, as well as on the properties of pulsating white dwarfs and the asteroseismological results that can be inferred.

A CROSS-MATCH OF 2MASS AND SDSS. II. PECULIAR L DWARFS, UNRESOLVED BINARIES, AND THE SPACE DENSITY OF T DWARF SECONDARIES

International Nuclear Information System (INIS)

Geissler, Kerstin; Metchev, Stanimir; Kirkpatrick, J. Davy; Berriman, G. Bruce; Looper, Dagny

2011-01-01

We present the completion of a program to cross-correlate the Sloan Digital Sky Survey Data Release 1 (SDSS DR1) and Two-Micron All-Sky Survey (2MASS) Point Source Catalog in search for extremely red L and T dwarfs. The program was initiated by Metchev and collaborators, who presented the findings on all newly identified T dwarfs in SDSS DR1 and estimated the space density of isolated T0-T8 dwarfs in the solar neighborhood. In the current work, we present most of the L dwarf discoveries. Our red-sensitive (z - J ≥ 2.75 mag) cross-match proves to be efficient in detecting peculiarly red L dwarfs, adding two new ones, including one of the reddest known L dwarfs. Our search also nets a new peculiarly blue L7 dwarf and, surprisingly, two M8 dwarfs. We further broaden our analysis to detect unresolved binary L or T dwarfs through spectral template fitting to all L and T dwarfs presented here and in the earlier work by Metchev and collaborators. We identify nine probable binaries, six of which are new and eight harbor likely T dwarf secondaries. We combine this result with current knowledge of the mass ratio distribution and frequency of substellar companions to estimate an overall space density of 0.005-0.05 pc -3 for individual T0-T8 dwarfs.

Larch Dwarf Mistletoe (FIDL)

Science.gov (United States)

Jerome S. Beatty; Gregory M. Filip; Robert L. Mathiason

1997-01-01

Larch dwarf mistletoe (Arceuthobium laricis (Piper) St. John) is a common and damaging parasite of western larch (Larix occidentalis Nutt.) in the Pacific Northwest and southern British Columbia. Larch dwarf mistletoe occurs commonly throughout the range of western larch in British Columbia, northern and central Idaho, western Montana and east of the Cascades in...

Star Formation Histories of Nearby Dwarf Galaxies

OpenAIRE

Grebel, Eva K.

2000-01-01

Properties of nearby dwarf galaxies are briefly discussed. Dwarf galaxies vary widely in their star formation histories, the ages of their subpopulations, and in their enrichment history. Furthermore, many dwarf galaxies show evidence for spatial variations in their star formation history; often in the form of very extended old populations and radial gradients in age and metallicity. Determining factors in dwarf galaxy evolution appear to be both galaxy mass and environment. We may be observi...

Evolution models of helium white dwarf--main-sequence star merger remnants: the mass distribution of single low-mass white dwarfs

OpenAIRE

Zhang, Xianfei; Hall, Philip D.; Jeffery, C. Simon; Bi, Shaolan

2017-01-01

It is not known how single white dwarfs with masses less than 0.5Msolar -- low-mass white dwarfs -- are formed. One way in which such a white dwarf might be formed is after the merger of a helium-core white dwarf with a main-sequence star that produces a red giant branch star and fails to ignite helium. We use a stellar-evolution code to compute models of the remnants of these mergers and find a relation between the pre-merger masses and the final white dwarf mass. Combining our results with ...

Hemlock Dwarf Mistletoe (FIDL)

Science.gov (United States)

Paul E. Hennon; Jerome S. Beatty; Diane Hildebrand

2001-01-01

Hemlock dwarf mistletoe, Arceuthobium tsugense (Rosendahl) G.N. Jones, causes a serious disease of western hemlock and several other tree species along the Pacific Coast of North America. This small, seed-bearing plant lives exclusively as a parasite on living trees. Throughout its range, hemlock dwarf mistletoe occurs in patch-like patterns in the forests. Some...

Merging white dwarfs and thermonuclear supernovae.

Science.gov (United States)

van Kerkwijk, M H

2013-06-13

Thermonuclear supernovae result when interaction with a companion reignites nuclear fusion in a carbon-oxygen white dwarf, causing a thermonuclear runaway, a catastrophic gain in pressure and the disintegration of the whole white dwarf. It is usually thought that fusion is reignited in near-pycnonuclear conditions when the white dwarf approaches the Chandrasekhar mass. I briefly describe two long-standing problems faced by this scenario, and the suggestion that these supernovae instead result from mergers of carbon-oxygen white dwarfs, including those that produce sub-Chandrasekhar-mass remnants. I then turn to possible observational tests, in particular, those that test the absence or presence of electron captures during the burning.

Understanding the immune system architecture and transcriptome responses to southern rice black-streaked dwarf virus in Sogatella furcifera.

Science.gov (United States)

Wang, Lin; Tang, Nan; Gao, Xinlei; Guo, Dongyang; Chang, Zhaoxia; Fu, Yating; Akinyemi, Ibukun A; Wu, Qingfa

2016-11-02

Sogatella furcifera, the white-backed planthopper (WBPH), has become one of the most destructive pests in rice production owing to its plant sap-sucking behavior and efficient transmission of Southern rice black-streaked dwarf virus (SRBSDV) in a circulative, propagative and persistent manner. The dynamic and complex SRBSDV-WBPH-rice plant interaction is still poorly understood. In this study, based on a homology-based genome-wide analysis, 348 immune-related genes belonging to 28 families were identified in WBPH. A transcriptome analysis of non-viruliferous (NVF) and viruliferous groups with high viral titers (HVT) and median viral titers (MVT) revealed that feeding on SRBSDV-infected rice plants has a significant impact on gene expression, regardless of viral titers in insects. We identified 278 up-regulated and 406 down-regulated genes shared among the NVF, MVT, and HVT groups and detected significant down-regulation of primary metabolism-related genes and oxidoreductase. In viruliferous WBPH with viral titer-specific transcriptome changes, 1,906 and 1,467 genes exhibited strict monotonically increasing and decreasing expression, respectively. The RNAi pathway was the major antiviral response to increasing viral titers among diverse immune responses. These results clarify the responses of immune genes and the transcriptome of WBPH to SRBSDV and improve our knowledge of the functional relationship between pathogen, vector, and host.

A radio-pulsing white dwarf binary star.

Science.gov (United States)

Marsh, T R; Gänsicke, B T; Hümmerich, S; Hambsch, F-J; Bernhard, K; Lloyd, C; Breedt, E; Stanway, E R; Steeghs, D T; Parsons, S G; Toloza, O; Schreiber, M R; Jonker, P G; van Roestel, J; Kupfer, T; Pala, A F; Dhillon, V S; Hardy, L K; Littlefair, S P; Aungwerojwit, A; Arjyotha, S; Koester, D; Bochinski, J J; Haswell, C A; Frank, P; Wheatley, P J

2016-09-15

White dwarfs are compact stars, similar in size to Earth but approximately 200,000 times more massive. Isolated white dwarfs emit most of their power from ultraviolet to near-infrared wavelengths, but when in close orbits with less dense stars, white dwarfs can strip material from their companions and the resulting mass transfer can generate atomic line and X-ray emission, as well as near- and mid-infrared radiation if the white dwarf is magnetic. However, even in binaries, white dwarfs are rarely detected at far-infrared or radio frequencies. Here we report the discovery of a white dwarf/cool star binary that emits from X-ray to radio wavelengths. The star, AR Scorpii (henceforth AR Sco), was classified in the early 1970s as a δ-Scuti star, a common variety of periodic variable star. Our observations reveal instead a 3.56-hour period close binary, pulsing in brightness on a period of 1.97 minutes. The pulses are so intense that AR Sco's optical flux can increase by a factor of four within 30 seconds, and they are also detectable at radio frequencies. They reflect the spin of a magnetic white dwarf, which we find to be slowing down on a 10 7 -year timescale. The spin-down power is an order of magnitude larger than that seen in electromagnetic radiation, which, together with an absence of obvious signs of accretion, suggests that AR Sco is primarily spin-powered. Although the pulsations are driven by the white dwarf's spin, they mainly originate from the cool star. AR Sco's broadband spectrum is characteristic of synchrotron radiation, requiring relativistic electrons. These must either originate from near the white dwarf or be generated in situ at the M star through direct interaction with the white dwarf's magnetosphere.

Crop-associated virus reduces the rooting depth of non-crop perennial native grass more than non-crop-associated virus with known viral suppressor of RNA silencing (VSR).

Science.gov (United States)

Malmstrom, Carolyn M; Bigelow, Patrick; Trębicki, Piotr; Busch, Anna K; Friel, Colleen; Cole, Ellen; Abdel-Azim, Heba; Phillippo, Colin; Alexander, Helen M

2017-09-15

As agricultural acreage expanded and came to dominate landscapes across the world, viruses gained opportunities to move between crop and wild native plants. In the Midwestern USA, virus exchange currently occurs between widespread annual Poaceae crops and remnant native perennial prairie grasses now under consideration as bioenergy feedstocks. In this region, the common aphid species Rhopalosiphum padi L. (the bird cherry-oat aphid) transmits several virus species in the family Luteoviridae, including Barley yellow dwarf virus (BYDV-PAV, genus Luteovirus) and Cereal yellow dwarf virus (CYDV-RPV and -RPS, genus Polerovirus). The yellow dwarf virus (YDV) species in these two genera share genetic similarities in their 3'-ends, but diverge in the 5'-regions. Most notably, CYDVs encode a P0 viral suppressor of RNA silencing (VSR) absent in BYDV-PAV. Because BYDV-PAV has been reported more frequently in annual cereals and CYDVs in perennial non-crop grasses, we examine the hypothesis that the viruses' genetic differences reflect different affinities for crop and non-crop hosts. Specifically, we ask (i) whether CYDVs might persist within and affect a native non-crop grass more strongly than BYDV-PAV, on the grounds that the polerovirus VSR could better moderate the defenses of a well-defended perennial, and (ii) whether the opposite pattern of effects might occur in a less defended annual crop. Because previous work found that the VSR of CYDV-RPS possessed greater silencing suppressor efficiency than that of CYDV-RPV, we further explored (iii) whether a novel grass-associated CYDV-RPS isolate would influence a native non-crop grass more strongly than a comparable CYDV-RPV isolate. In growth chamber studies, we found support for this hypothesis: only grass-associated CYDV-RPS stunted the shoots and crowns of Panicum virgatum L. (switchgrass), a perennial native North American prairie grass, whereas crop-associated BYDV-PAV (and coinfection with BYDV-PAV and CYDV-RPS) most

White-dwarf-white-dwarf galactic background in the LISA data

International Nuclear Information System (INIS)

Edlund, Jeffrey A.; Tinto, Massimo; Krolak, Andrzej; Nelemans, Gijs

2005-01-01

LISA (Laser Interferometer Space Antenna) is a proposed space mission, which will use coherent laser beams exchanged between three remote spacecraft to detect and study low-frequency cosmic gravitational radiation. In the low part of its frequency band, the LISA strain sensitivity will be dominated by the incoherent superposition of hundreds of millions of gravitational wave signals radiated by inspiraling white-dwarf binaries present in our own Galaxy. In order to estimate the magnitude of the LISA response to this background, we have simulated a synthesized population that recently appeared in the literature. Our approach relies on entirely analytic expressions of the LISA time-delay interferometric responses to the gravitational radiation emitted by such systems, which allows us to implement a computationally efficient and accurate simulation of the background in the LISA data. We find the amplitude of the galactic white-dwarf binary background in the LISA data to be modulated in time, reaching a minimum equal to about twice that of the LISA noise for a period of about two months around the time when the Sun-LISA direction is roughly oriented towards the Autumn equinox. This suggests that, during this time period, LISA could search for other gravitational wave signals incoming from directions that are away from the galactic plane. Since the galactic white-dwarf background will be observed by LISA not as a stationary but rather as a cyclostationary random process with a period of 1 yr, we summarize the theory of cyclostationary random processes, present the corresponding generalized spectral method needed to characterize such process, and make a comparison between our analytic results and those obtained by applying our method to the simulated data. We find that, by measuring the generalized spectral components of the white-dwarf background, LISA will be able to infer properties of the distribution of the white-dwarf binary systems present in our Galaxy

Response of dwarf mistletoe-infested ponderosa pine to thinning: 2. Dwarf mistletoe propagation.

Science.gov (United States)

Lewis F. Roth; James W. Barrett

1985-01-01

Propagation of dwarf mistletoe in ponderosa pine saplings is little influenced by thinning overly dense stands to 250 trees per acre. Numerous plants that appear soon after thinning develop from formerly latent plants in the suppressed under-story. Subsequently, dwarf mistletoe propagates nearly as fast as tree crowns enlarge but the rate differs widely among trees....

Viruses and their significance in agricultural and horticultural crops in Finland

Directory of Open Access Journals (Sweden)

E. TAPIO

2008-12-01

Full Text Available This paper reviews the plant viruses and virus vectors that have been detected in agricultural and horticultural crop plants and some weeds in Finland. The historical and current importance of virus diseases and the methods used for controlling them in cereals, potato, berry plants, fruit trees, ornamental plants and vegetables are discussed. Plant viruses have been intensely studied in Finland over 40 years. Up to date, 44 plant virus species have been detected, and many tentatively identified virus-es are also reported. Control of many virus diseases has been significantly improved. This has been achieved mainly through changes in cropping systems, production of healthy seed potatoes and healthy stocks of berry plants, fruit trees and ornamental plants in the institutes set up for such production, and improved hygiene. At the present, barley yellow dwarf luteovirus, potato Y potyvirus and potato mop-top furovirus are considred to be economically the most harmful plant viruses in Finland.

What fraction of white dwarfs are members of binary systems?

International Nuclear Information System (INIS)

Holberg, J B

2009-01-01

White dwarfs were originally discovered as the subordinate faint companions of bright nearby stars (i.e. Sirius B and 40 Eri B). Several general categories of binary systems involving white dwarfs are recognized: Sirius-like systems, where the white dwarf may be difficult to detect, binary systems containing white dwarfs and low mass stars, where the white dwarf is often readily discerned; and double degenerate systems. Different modes of white dwarf discovery influence our perception of both the overall binary fraction and the nature of these systems; proper motion surveys emphasize resolved systems, while photometric surveys emphasize unresolved systems containing relatively hot white dwarfs. Recent studies of the local white dwarf population offer some hope of achieving realistic estimates of the relative number of binary systems containing white dwarfs. A sample of 132 white dwarfs within 20 pc indicates that an individual white dwarf has a probability of 32 ± 8% of occurring within a binary or multiple star system.

Southern rice black-streaked dwarf virus (SRBSDV) directly affects the feeding and reproduction behavior of its vector, Sogatella furcifera (Horváth) (Hemiptera: Delphacidae).

Science.gov (United States)

Xu, Hongxing; He, Xiaochan; Zheng, Xusong; Yang, Yajun; Tian, Junce; Lu, Zhongxian

2014-03-24

Southern rice black-streaked dwarf virus (SRBSDV) is a recently discovered member of the genus Fijivirus and it is transmitted by the rice whitebacked planthopper (WBPH), Sogatella furcifera (Horváth). It was found that SRBSDV infected vectors might contribute negatively to the WBPH population, although the longer nymphal period might benefit viral acquisition, transmission and increase infection rate. The interaction between SRBSDV and its vector need to be further explored to gain better understanding of the dispersal of WBPH and the spread of virus disease, in particular the feeding and reproduction behavior of viruliferous WBPH. Newly hatched nymphs of WBPH were fed on healthy rice plant after feeding on SRBSDV-infected rice plants for 2 h, and newly emerged adults were numbered and tested. Feeding behaviors of WBPH adults were monitored electronically within a Faraday cage using a Giga-4 DC EPG amplifier. The newly emerged adults were paired, and the fecundity and egg hatchability were investigated. WBPH was molecularly identified for SRBSDV when they dead. According to the identification results, data on viruliferous and non-viruliferous WBPH were collected and analyzed. Feeding behavior of viruliferous WBPH was different from those of non-viruliferous WBPH. Frequency of phloem sap ingestion of viruliferous WBPH increased significantly, however the total feeding duration did not increase markedly. When both WBPH parents were infected with SRBSDV, their fecundity and hatchability of the eggs produced were significant lower than those of normal WBPH parents. However, if only one of the parents was viruliferous, fecundity and egg hatchability were only slightly affected. Viruliferous WBPH fed on the phloem more frequently than non-viruliferous WBPH and can thus contribute to virus transmission. When both vector parents are viruliferous fecundity and hatchability of the eggs were significantly reduced. However when only one of the parents WBPH was viruliferous

Activity-induced radial velocity variation of M dwarf stars

DEFF Research Database (Denmark)

Andersen, Jan Marie; Korhonen, Heidi Helena

2012-01-01

that can drown out a planetary signature. Cool, low-mass M dwarf stars can be highly active, which can make detection of potentially habitable planets around these stars difficult. We investigate radial velocity variations caused by different activity (spot) patterns on M dwarf stars in order to determine...... the limits of detectability for small planets orbiting active M dwarfs. We report on our progress toward the aim of answering the following questions: What types of spot patterns are realistic for M dwarf stars? What effect will spots have on M dwarf RV measurements? Can jitter from M dwarf spots mimic...... planetary signals? What is the ideal observing wavelength to reduce M dwarf jitter?...

NEW COOLING SEQUENCES FOR OLD WHITE DWARFS

International Nuclear Information System (INIS)

Renedo, I.; Althaus, L. G.; GarcIa-Berro, E.; Miller Bertolami, M. M.; Romero, A. D.; Corsico, A. H.; Rohrmann, R. D.

2010-01-01

We present full evolutionary calculations appropriate for the study of hydrogen-rich DA white dwarfs. This is done by evolving white dwarf progenitors from the zero-age main sequence, through the core hydrogen-burning phase, the helium-burning phase, and the thermally pulsing asymptotic giant branch phase to the white dwarf stage. Complete evolutionary sequences are computed for a wide range of stellar masses and for two different metallicities, Z = 0.01, which is representative of the solar neighborhood, and Z = 0.001, which is appropriate for the study of old stellar systems, like globular clusters. During the white dwarf cooling stage, we self-consistently compute the phase in which nuclear reactions are still important, the diffusive evolution of the elements in the outer layers and, finally, we also take into account all the relevant energy sources in the deep interior of the white dwarf, such as the release of latent heat and the release of gravitational energy due to carbon-oxygen phase separation upon crystallization. We also provide colors and magnitudes for these sequences, based on a new set of improved non-gray white dwarf model atmospheres, which include the most up-to-date physical inputs like the Lyα quasi-molecular opacity. The calculations are extended down to an effective temperature of 2500 K. Our calculations provide a homogeneous set of evolutionary cooling tracks appropriate for mass and age determinations of old DA white dwarfs and for white dwarf cosmochronology of the different Galactic populations.

Calorie restriction and dwarf mice in gerontological research.

Science.gov (United States)

McKee Alderman, J; DePetrillo, Michael A; Gluesenkamp, Angela M; Hartley, Antonia C; Verhoff, S Veronica; Zavodni, Katherine L; Combs, Terry P

2010-01-01

What aging process is delayed by calorie restriction (CR) and mutations that produce long-lived dwarf mice? From 1935 until 1996, CR was the only option for increasing the maximum lifespan of laboratory rodents. In 1996, the mutation producing the Ames dwarf mouse (Prop-1(-/-)) was reported to increase lifespan. Since 1996, other gene mutations that cause dwarfism or lower body weight have been reported to increase the lifespan of mice. The recent discovery of long-lived mutant dwarf mice provides an opportunity to investigate common features between CR and dwarf models. Both CR and dwarf mutations increase insulin sensitivity. Elevated insulin sensitivity reduces oxidative stress, a potential cause of aging. The elevation of liver insulin sensitivity by the hormone adiponectin in CR and long-lived dwarf mice can lower endogenous glucose production and raise fatty acid oxidation. Adiponectin reduction of plasma glucose in CR and long-lived dwarf mice can thereby lower age-related increases in oxidative damage and cancer. Copyright 2009 S. Karger AG, Basel.

Starbursts in Blue compact dwarf galaxies

International Nuclear Information System (INIS)

Thuan, T.X.

1987-01-01

We summarize all the arguments for a bursting mode of star formation in blue compact dwarf galaxies. We show in particular how spectral synthesis of far ultraviolet spectra of Blue compact dwarf galaxy constitutes a powerful way for studying the star formation history in these galaxies. Blue compact dwarf galaxy luminosity functions show jumps and discontinuities. These jumps act like fossil records of the star-forming bursts, helping us to count and date the bursts

Merging White Dwarfs and Thermonuclear Supernovae

OpenAIRE

van Kerkwijk, Marten H.

2012-01-01

Thermonuclear supernovae result when interaction with a companion reignites nuclear fusion in a carbon-oxygen white dwarf, causing a thermonuclear runaway, a catastrophic gain in pressure, and the disintegration of the whole white dwarf. It is usually thought that fusion is reignited in near-pycnonuclear conditions when the white dwarf approaches the Chandrasekhar mass. I briefly describe two long-standing problems faced by this scenario, and our suggestion that these supernovae instead resul...

Rare White dwarf stars with carbon atmospheres

OpenAIRE

Dufour, P.; Liebert, James; Fontaine, G.; Behara, N.

2007-01-01

White dwarfs represent the endpoint of stellar evolution for stars with initial masses between approximately 0.07 msun and 8-10 msun, where msun is the mass of the Sun (more massive stars end their life as either black holes or neutron stars). The theory of stellar evolution predicts that the majority of white dwarfs have a core made of carbon and oxygen, which itself is surrounded by a helium layer and, for ~80 per cent of known white dwarfs, by an additional hydrogen layer. All white dwarfs...

Pulsating White Dwarfs in Cataclysmic Variables: The Marriage of ZZ Cet and Dwarf Nova

OpenAIRE

Warner, Brian; Woudt, Patrick A.

2003-01-01

There are now four dwarf novae known with white dwarf primaries that show large amplitude non-radial oscillations of the kind seen in ZZ Cet stars. We compare the properties of these stars and point out that by the end of the Sloan Digital Sky Survey more than 30 should be known.

Pulsations in carbon-atmosphere white dwarfs: A new chapter in white dwarf asteroseismology

International Nuclear Information System (INIS)

Fontaine, G; Brassard, P; Dufour, P; Green, E M; Liebert, J

2009-01-01

We present some of the results of a survey aimed at exploring the asteroseismological potential of the newly-discovered carbon-atmosphere white dwarfs. We show that, in certains regions of parameter space, carbon-atmosphere white dwarfs may drive low-order gravity modes. We demonstrate that our theoretical results are consistent with the recent exciting discovery of luminosity variations in SDSS J1426+5752 and some null results obtained by a team of scientists at McDonald Observatory. We also present follow-up photometric observations carried out by ourselves at the Mount Bigelow 1.6-m telescope using the new Mont4K camera. The results of follow-up spectroscopic observations at the MMT are also briefly reported, including the surprising discovery that SDSS J1426+5752 is not only a pulsating star but that it is also a magnetic white dwarf with a surface field near 1.2 MG. The discovery of g-mode pulsations in SDSS J1426+5752 is quite significant in itself as it opens a fourth asteroseismological 'window', after the GW Vir, V777 Her, and ZZ Ceti families, through which one may study white dwarfs.

The RSA survey of dwarf galaxies, 1: Optical photometry

Science.gov (United States)

Vader, J. Patricia; Chaboyer, Brian

1994-01-01

We present detailed surface photometry, based on broad B-band charge coupled device (CCD) images, of about 80 dwarf galaxies. Our sample represents approximately 10% of all dwarf galaxies identified in the vicinity of Revised Shapley-Ames (RSA) galaxies on high resolution blue photographic plates, referred to as the RSA survey of dwarf galaxies. We derive global properties and radial surface brightness profiles, and examine the morphologies. The radial surface brightness profiles of dwarf galaxies, whether early or late type, display the same varieties in shape and complexity as those of classical giant galaxies. Only a few are well described by a pure r(exp 1/4) law. Exponential profiles prevail. Features typical of giant disk galaxies, such as exponential profiles with a central depression, lenses, and even, in one case (IC 2041), a relatively prominent bulge are also found in dwarf galaxies. Our data suggest that the central region evolves from being bulge-like, with an r(exp 1/4) law profile, in bright galaxies to a lens-like structure in dwarf galaxies. We prove detailed surface photometry to be a helpful if not always sufficient tool in investigating the structure of dwarf galaxies. In many cases kinematic information is needed to complete the picture. We find the shapes of the surface brightness profiles to be loosely associated with morphological type. Our sample contains several new galaxies with properties intermediate between those of giant and dwarf ellipticals (but no M32-like objects). This shows that such intermediate galaxies exist so that at least a fraction of early-type dwarf ellipticals is structurally related to early-type giants instead of belonging to a totally unrelated, disjunct family. This supports an origin of early-type dwarf galaxies as originally more massive systems that acquired their current morphology as a result of substantial, presumable supernova-driven, mass loss. On the other hand, several early-type dwarfs in our sample are

The WFCAM transit survey and cool white dwarfs

Directory of Open Access Journals (Sweden)

Pinfield D.

2013-04-01

Full Text Available We present results from our search for cool white dwarfs in the WTS (WFCAM Transit Survey. Repeat observations starting in 2007 allowed to produce deep stacked images in J and measure proper motions. We combine this with deep optical imaging to select cool white dwarf candidates (Teff < 5000 K. About 27 cool white dwarf candidates with proper motions above 0.10 arcsec/yr were identified in one of the fields representing 1/8th of the survey area. Follow-up spectroscopy with the 10.2 m GTC telescope at La Palma confirmed the white dwarf status for all observed candidates. On-going work is being carried out to increase the sample of cool white dwarfs that will allow a more comprehensive study of the thick disk/halo white dwarf population.

Production and evaluation of dwarf and semi-dwarf winter wheat mutants

International Nuclear Information System (INIS)

Barabas, Z.; Kertesz, Z.

1984-01-01

A special research programme for evolving and evaluating dwarf wheat forms resistant to lodging was carried out at the Cereal Research Institute, Wheat Division, Szeged, Hungary. Seed lots of the two tall winter wheat varieties Jubilejnaya 50 and Partizanka were exposed to gamma ray of 60 Co. With irradiation of 15000 rad 60 Co all of M 1 plants grown in the field were almost totally destroyed in 1980 and about 50% in 1982. In the greenhouse the number of lost M 1 plants was insignificant. Only a small number of plants died both in the greenhouse and in the field when they were irradiated with 5000 rad. A treatment with this lower dose of irradiation probably may help the breeders in selection for winter hardiness. 97 dwarf wheat lines already established were analysed for height character by a top cross method using the variety Jubilejnaya 50 as a tester. Height data of the simultaneously grown parental as well as the F 1 and F 2 offsprings indicated that the majority of them were recessive, except 3 cases where dominant or semi-dominant dwarfism was observed. Noteworthy is the Mx 158 a new semi-dwarf variety candidate, 60-65 cm in height at normal stand and resistant to all the main diseases here (powdery mildew and rusts). Its grain and protein production per unit area is also very good. Some genetically lesser-known dwarf sources were investigated in a complete crossing diallel test. (author)

WISE Y dwarfs as probes of the brown dwarf-exoplanet connection

International Nuclear Information System (INIS)

Beichman, C.; Gelino, Christopher R.; Kirkpatrick, J. Davy; Cushing, Michael C.; Dodson-Robinson, Sally; Marley, Mark S.; Morley, Caroline V.; Wright, E. L.

2014-01-01

We have determined astrometric positions for 15 WISE-discovered late-type brown dwarfs (six T8-9 and nine Y dwarfs) using the Keck-II telescope, the Spitzer Space Telescope, and the Hubble Space Telescope. Combining data from 8 to 20 epochs we derive parallactic and proper motions for these objects, which puts the majority within 15 pc. For ages greater than a few Gyr, as suggested from kinematic considerations, we find masses of 10-30 M Jup based on standard models for the evolution of low-mass objects with a range of mass estimates for individual objects, depending on the model in question. Three of the coolest objects have effective temperatures ∼350 K and inferred masses of 10-15 M Jup . Our parallactic distances confirm earlier photometric estimates and direct measurements and suggest that the number of objects with masses below about 15 M Jup must be flat or declining, relative to higher mass objects. The masses of the coldest Y dwarfs may be similar to those inferred for recently imaged planet-mass companions to nearby young stars. Objects in this mass range, which appear to be rare in both the interstellar and protoplanetary environments, may both have formed via gravitational fragmentation—the brown dwarfs in interstellar clouds and companion objects in a protoplanetary disk. In both cases, however, the fact that objects in this mass range are relatively infrequent suggests that this mechanism must be inefficient in both environments.

Morphology and Structures of Nearby Dwarf Galaxies

Science.gov (United States)

Seo, Mira; Ann, HongBae

2015-08-01

We performed an analysis of the structure of nearby dwarf galaxies based on a 2-dimensional decomposition of galaxy images using GALFIT. The present sample consists of ~1,100 dwarf galaxies with redshift less than z = 0.01, which is is derived from the morphology catalog of the Visually classified galaxies in the local universe (Ann, Seo, and Ha 2015). In this catalog, dwarf galaxies are divided into 5 subtypes: dS0, dE, dSph, dEbc, dEblue with distinction of the presence of nucleation in dE, dSph, and dS0. We found that dSph and dEblue galaxies are fainter than other subtypes of dwarf galaxies. In most cases, single component, represented by the Sersic profile with n=1~1.5, well describes the luminosity distribution of dwarf galaxies in the present sample. However, a significant fraction of dS0, dEbc, and dEbue galaxies show sub-structures such as spiral arms and rings. We will discuss the morphology dependent evolutionary history of the local dwarf galaxies.

High-dispersion observations of H-alpha in the suspected brown dwarf, white dwarf binary system G29-38

International Nuclear Information System (INIS)

Liebert, J.; Saffer, R.A.; Pilachowski, C.A.

1989-01-01

High-dispersion spectroscopy of the H-alpha absorption line of the cool DA white dwarf G29-38 is reported. This is the star for which a recently detected IR excess has been suggested to be due to a possible brown dwarf companion. Three echelle spectra show no evidence for radial-velocity variations larger than about 1.1 + or - 8.7 km/s and are used to derive a weighted heliocentric radial velocity of 33.7 + or - 4.3 kms/s for the white dwarf. The observations of a sharp absorption-line core restricts the possible rotation of the white dwarf to 40 km/s or less and ensures that any surface magnetic field has a strength of 100,000 G or less. These results make it unlikely that the DA white dwarf has previously been in a cataclysmic variable accretion phase. 18 references

HOW TO MAKE AN ULTRA-FAINT DWARF SPHEROIDAL GALAXY: TIDAL STIRRING OF DISKY DWARFS WITH SHALLOW DARK MATTER DENSITY PROFILES

International Nuclear Information System (INIS)

Łokas, Ewa L.; Kazantzidis, Stelios; Mayer, Lucio

2012-01-01

In recent years the Sloan Digital Sky Survey has unraveled a new population of ultra-faint dwarf galaxies (UFDs) whose origin remains a puzzle in the vicinity of the Milky Way (MW). Using a suite of collisionless N-body simulations, we investigate the formation of UFDs in the context of the tidal stirring model for the formation of dwarf spheroidal galaxies in the Local Group (LG). Our simulations are designed to reproduce the tidal interactions between MW-sized host galaxies and rotationally supported dwarfs embedded in 10 9 M ☉ dark matter (DM) halos. We explore a variety of inner density slopes ρ∝r –α for the dwarf DM halos, ranging from core-like (α = 0.2) to cuspy (α = 1), and different dwarf orbital configurations. Our experiments demonstrate that UFDs can be produced via tidal stirring of disky dwarfs on relatively tight orbits, consistent with a redshift of accretion by the host galaxy of z ∼ 1, and with intermediate values for the halo inner density slopes (ρ∝r –0.6 ). The inferred slopes are in excellent agreement with those resulting from both the modeling of the rotation curves of dwarf galaxies and recent cosmological simulations of dwarf galaxy formation. Comparing the properties of observed UFDs with those of their simulated counterparts, we find remarkable similarities in terms of basic observational parameters. We conclude that tidal stirring of rotationally supported dwarfs represents a viable mechanism for the formation of UFDs in the LG environment.

Progenitors of white dwarfs

International Nuclear Information System (INIS)

Drilling, J.S.; Schoenberner, D.

1985-01-01

Direct observational evidence is presented which indicates that the immediate progenitors of white dwarfs are the central stars of planetary nebulae (approximately 70%), other post-AGB objects (approximately 30%), and post-HB objects not massive enough to climb the AGB (approximately 0.3%). The combined birth rate for these objects is in satisfactory agreement with the death rate of main-sequence stars and the birth rate of white dwarfs

Explosive helium burning in white dwarf stars

Energy Technology Data Exchange (ETDEWEB)

Khokhlov, A.M. (AN SSSR, Moscow. Astronomicheskij Sovet)

1984-04-01

Helium burning kinetics in white dwarfs has been considered at constant temperatures T >= 10/sup 9/ K and densities rho >10/sup 5/ g/cm/sup 3/. It is found, that helium detonation in white dwarfs does not lead to formation of light (A < 56) elements. Thus, helium white dwarf model for supernova 1 is inconsistent with observations.

Project DWARF - using eclipsing binaries for searching for exoplanets and brown dwarfs

Science.gov (United States)

Kudak, V.; Parimucha, Š.

2016-12-01

Project DWARF is a long-term observation campaign for about 60 selected eclipsing binaries aimed for detection of exoplanets or other objects (brown dwarfs) in low-mass detached binaries of different types (low-mass eclipsing binaries with M and K components, short-period binaries with sdB or sdO component, post-common-envelope systems containing a white dwarf). Existence of other bodies in systems are determined by analysing of O-C diagrams, constructed from observed minima times of binaries. Objects are selected with intention to determine minima with high precision. About 40 observatories are involved into the network at present time, mostly situated in Europe. The observations are made by small or middle class telescopes with apertures of 20-200 cm. In this contribution we give information about current status of the project, we present main goals and results of 4 years observations.

Evaluation of the Possibility of Cultivation of Eggplant and Common Vetch in a Mercury Contaminated Area; Evaluacion de la posibilidad de cultivo de veza y berenjena en un area contaminada con mercurio

Energy Technology Data Exchange (ETDEWEB)

Sierra, M J; Millan, R; Esteban, E

2006-12-18

This study is framed in the project Recuperacion de Terrenos Afectados por Mercurio Ambiental (RETAMA) which determines the behaviour of mercury in the soil-plant system within the area of Almaden. It forms part of experimental work of doctoral thesis carried out by Maria Jose Sierra and directed by Rocio Millan and Elvira Esteban. The objective of this work was to study the mercury absorption capacity of Solanum melongena (eggplant) and Vicia sativa (common vetch), and the distribution of this metal in this crop. The possible use of eggplant culture as an economic alternative in a mercury contaminated area has been evaluated. The present study has been carried out using a soil from the mercury mining district of Almaden (Spain). The total mercury concentration of this soil is 14.16 + 0.65 mg kg-1 on average. The selected crops are typical in the area of study, eggplant is much appreciated for human consumption and common vetch is an important forage crop. At the end of the document (Anexo V) a critical reading of several articles related to the study subject have been enclosed. (Author) 50 refs.

A Survey for Hα Emission from Late L Dwarfs and T Dwarfs

Science.gov (United States)

Pineda, J. Sebastian; Hallinan, Gregg; Kirkpatrick, J. Davy; Cotter, Garret; Kao, Melodie M.; Mooley, Kunal

2016-07-01

Recently, studies of brown dwarfs have demonstrated that they possess strong magnetic fields and have the potential to produce radio and optical auroral emissions powered by magnetospheric currents. This emission provides the only window on magnetic fields in the coolest brown dwarfs and identifying additional benchmark objects is key to constraining dynamo theory in this regime. To this end, we conducted a new red optical (6300-9700 Å) survey with the Keck telescopes looking for Hα emission from a sample of late L dwarfs and T dwarfs. Our survey gathered optical spectra for 29 targets, 18 of which did not have previous optical spectra in the literature, greatly expanding the number of moderate-resolution (R ˜ 2000) spectra available at these spectral types. Combining our sample with previous surveys, we confirm an Hα detection rate of 9.2±{}2.13.5% for L and T dwarfs in the optical spectral range of L4-T8. This detection rate is consistent with the recently measured detection rate for auroral radio emission from Kao et al., suggesting that geometrical selection effects due to the beaming of the radio emission are small or absent. We also provide the first detection of Hα emission from 2MASS 0036+1821, previously notable as the only electron cyclotron maser radio source without a confirmed detection of Hα emission. Finally, we also establish optical standards for spectral types T3 and T4, filling in the previous gap between T2 and T5. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

Polarized radiation in magnetic white dwarfs

International Nuclear Information System (INIS)

Rosi, L.A.; Zimmerman, R.L.; Kemp, J.C.

1976-01-01

A model for magnetic white dwarfs is proposed which attributes the partially polarized light to synchrotron radiation. The source of the radiation is relativistic electrons trapped in the magnetosphere of a white dwarf. The white dwarf's magnetic field is assumed to be dipolar. The Stokes parameters for the synchrotron radiation are tabulated as a function of frequency, observer's orientation, and energy and spatial distribution of the relativistic electrons. The results of the synchrotron calculations are applied to the polarization observations of Grw+70degree8247 and DQ Herculis. This model can account for the major features of the polarized radiation coming from these two magnetic white dwarfs. The calculations predict for Grw+70degree8247 that the surface magnetic field is B/sub s/approximately-less-than4 x 10 6 gauss, that the incident viewing angle is 45degreeapproximately-less-thantheta 0 approximately-less-than75degree, and that the electrons are trapped with nearly an isotropic distribution about the white dwarf. For DQ Herculis the surface magnetic field is B/sub s/approximately-less-than7 x 10 6 gauss and the trapped electrons are confined to a dislike region about the white dwarf. For both cases the density of electrons in the magnetosphere falls in the range of 10 5 approximately-less-thannapproximately-less-than10 7 cm -3 with energies of about 4--35 MeV

EVOLUTIONARY TRACKS OF TIDALLY STIRRED DISKY DWARF GALAXIES

International Nuclear Information System (INIS)

Lokas, Ewa L.; Kazantzidis, Stelios; Mayer, Lucio

2011-01-01

Using collisionless N-body simulations, we investigate the tidal evolution of late-type, rotationally supported dwarfs inside Milky Way sized host galaxies. Our study focuses on a wide variety of dwarf orbital configurations and initial structures. During the evolution, the disky dwarfs undergo strong mass loss, the stellar disks are transformed into spheroids, and rotation is replaced by random motions of the stars. Thus, the late-type progenitors are transformed into early-type dwarfs as envisioned by the tidal stirring model for the formation of dwarf spheroidal (dSph) galaxies in the Local Group. We determine the photometric properties of the dwarfs, including the total visual magnitude, the half-light radius, and the central surface brightness as they would be measured by an observer near the galactic center. Special emphasis is also placed on studying their kinematics and shapes. We demonstrate that the measured values are biased by a number of observational effects including the increasing angle of the observation cone near the orbital pericenter, the fact that away from the pericenter the tidal tails are typically oriented along the line of sight, and the fact that for most of the evolution the stellar components of the dwarfs are triaxial ellipsoids whose major axis tumbles with respect to the line of sight. Finally, we compare the measured properties of the simulated dwarfs to those of dwarf galaxies in the Local Group. The evolutionary tracks of the dwarfs in different parameter planes and the correlations between their different properties, especially the total magnitude and the surface brightness, strongly suggest that present-day dSph galaxies may have indeed formed from late-type progenitors as proposed by the tidal stirring scenario.

A DARK SPOT ON A MASSIVE WHITE DWARF

Energy Technology Data Exchange (ETDEWEB)

Kilic, Mukremin; Gianninas, Alexandros; Curd, Brandon; Wisniewski, John P. [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W. Brooks St., Norman, OK 73019 (United States); Bell, Keaton J.; Winget, D. E.; Winget, K. I. [Department of Astronomy, University of Texas at Austin, Austin, TX 78712 (United States); Brown, Warren R. [Smithsonian Astrophysical Observatory, 60 Garden St., Cambridge, MA 02138 (United States); Hermes, J. J. [Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom); Dufour, Patrick [Institut de recherche sur les exoplanétes (iREx), Département de Physique, Université de Montréal, C.P. 6128, Succ. Centre-Ville, Montréal, QC H3C 3J7 (Canada)

2015-12-01

We present the serendipitous discovery of eclipse-like events around the massive white dwarf SDSS J152934.98+292801.9 (hereafter J1529+2928). We selected J1529+2928 for time-series photometry based on its spectroscopic temperature and surface gravity, which place it near the ZZ Ceti instability strip. Instead of pulsations, we detect photometric dips from this white dwarf every 38 minutes. Follow-up optical spectroscopy observations with Gemini reveal no significant radial velocity variations, ruling out stellar and brown dwarf companions. A disintegrating planet around this white dwarf cannot explain the observed light curves in different filters. Given the short period, the source of the photometric dips must be a dark spot that comes into view every 38 minutes due to the rotation of the white dwarf. Our optical spectroscopy does not show any evidence of Zeeman splitting of the Balmer lines, limiting the magnetic field strength to B < 70 kG. Since up to 15% of white dwarfs display kG magnetic fields, such eclipse-like events should be common around white dwarfs. We discuss the potential implications of this discovery on transient surveys targeting white dwarfs, like the K2 mission and the Large Synoptic Survey Telescope.

Effects of magnetic fields in white dwarfs

International Nuclear Information System (INIS)

Franzon, Bruno; Schramm, Stefan

2017-01-01

We perform calculations of white dwarfs endowed with strong magnetic fields. White dwarfs are the progenitors of supernova Type Ia explosions and they are widely used as candles to show that the Universe is expanding and accelerating. However, observations of ultraluminous supernovae have suggested that the progenitor of such an explosion should be a white dwarf with mass above the well-known Chandrasekhar limit ∼ 1.4 M⊙. In corroboration with other works, but by using a fully general relativistic framework, we obtained also strongly magnetized white dwarfs with masses M ∼ 2.0 M⊙. (paper)

Genetic identification of a dwarf mutant in cucumber ( Cucumis ...

African Journals Online (AJOL)

The dwarf (compact) plant architecture is an important trait in cucumber (Cucumis sativus L.) breeding. A dwarf type mutant was selected from the cucumbers. The morphological and reproductive characteristics of the dwarf were compared with the vine plants. The dwarf type of cucumbers is characterized by its short ...

Microlensing Binaries with Candidate Brown Dwarf Companions

DEFF Research Database (Denmark)

Shin, I.-G; Han, C.; Gould, A.

2012-01-01

masses of the brown dwarf companions are 0.02 ± 0.01 M⊙ and 0.019 ± 0.002 M⊙ for MOA-2011-BLG-104/OGLE-2011-BLG-0172 and MOA-2011-BLG-149, respectively, and both companions are orbiting low-mass M dwarf host stars. More microlensing brown dwarfs are expected to be detected as the number of lensing events...

Highly Specific Detection of Five Exotic Quarantine Plant Viruses using RT-PCR

Directory of Open Access Journals (Sweden)

Hoseong Choi

2013-03-01

Full Text Available To detect five plant viruses (Beet black scorch virus, Beet necrotic yellow vein virus, Eggplant mottled dwarf virus, Pelargonium zonate spot virus, and Rice yellow mottle virus for quarantine purposes, we designed 15 RT-PCR primer sets. Primer design was based on the nucleotide sequence of the coat protein gene, which is highly conserved within species. All but one primer set successfully amplified the targets, and gradient PCRs indicated that the optimal temperature for the 14 useful primer sets was 51.9°C. Some primer sets worked well regardless of annealing temperature while others required a very specific annealing temperature. A primer specificity test using plant total RNAs and cDNAs of other plant virus-infected samples demonstrated that the designed primer sets were highly specific and generated reproducible results. The newly developed RT-PCR primer sets would be useful for quarantine inspections aimed at preventing the entry of exotic plant viruses into Korea.

Maximum gravitational redshift of white dwarfs

International Nuclear Information System (INIS)

Shapiro, S.L.; Teukolsky, S.A.

1976-01-01

The stability of uniformly rotating, cold white dwarfs is examined in the framework of the Parametrized Post-Newtonian (PPN) formalism of Will and Nordtvedt. The maximum central density and gravitational redshift of a white dwarf are determined as functions of five of the nine PPN parameters (γ, β, zeta 2 , zeta 3 , and zeta 4 ), the total angular momentum J, and the composition of the star. General relativity predicts that the maximum redshifts is 571 km s -1 for nonrotating carbon and helium dwarfs, but is lower for stars composed of heavier nuclei. Uniform rotation can increase the maximum redshift to 647 km s -1 for carbon stars (the neutronization limit) and to 893 km s -1 for helium stars (the uniform rotation limit). The redshift distribution of a larger sample of white dwarfs may help determine the composition of their cores

Top 10 plant viruses in molecular plant pathology.

Science.gov (United States)

Scholthof, Karen-Beth G; Adkins, Scott; Czosnek, Henryk; Palukaitis, Peter; Jacquot, Emmanuel; Hohn, Thomas; Hohn, Barbara; Saunders, Keith; Candresse, Thierry; Ahlquist, Paul; Hemenway, Cynthia; Foster, Gary D

2011-12-01

Many scientists, if not all, feel that their particular plant virus should appear in any list of the most important plant viruses. However, to our knowledge, no such list exists. The aim of this review was to survey all plant virologists with an association with Molecular Plant Pathology and ask them to nominate which plant viruses they would place in a 'Top 10' based on scientific/economic importance. The survey generated more than 250 votes from the international community, and allowed the generation of a Top 10 plant virus list for Molecular Plant Pathology. The Top 10 list includes, in rank order, (1) Tobacco mosaic virus, (2) Tomato spotted wilt virus, (3) Tomato yellow leaf curl virus, (4) Cucumber mosaic virus, (5) Potato virus Y, (6) Cauliflower mosaic virus, (7) African cassava mosaic virus, (8) Plum pox virus, (9) Brome mosaic virus and (10) Potato virus X, with honourable mentions for viruses just missing out on the Top 10, including Citrus tristeza virus, Barley yellow dwarf virus, Potato leafroll virus and Tomato bushy stunt virus. This review article presents a short review on each virus of the Top 10 list and its importance, with the intent of initiating discussion and debate amongst the plant virology community, as well as laying down a benchmark, as it will be interesting to see in future years how perceptions change and which viruses enter and leave the Top 10. © 2011 The Authors. Molecular Plant Pathology © 2011 BSPP and Blackwell Publishing Ltd.

Axion cooling of white dwarfs

OpenAIRE

Isern, J.; Catalan, S.; Garcia--Berro, E.; Salaris, M.; Torres, S.

2013-01-01

The evolution of white dwarfs is a simple gravothermal process. This process can be tested in two ways, through the luminosity function of these stars and through the secular variation of the period of pulsation of those stars that are variable. Here we show how the mass of the axion can be constrained using the white dwarf luminosity function.

THE NIRSPEC ULTRACOOL DWARF RADIAL VELOCITY SURVEY

International Nuclear Information System (INIS)

Blake, Cullen H.; Charbonneau, David; White, Russel J.

2010-01-01

We report the results of an infrared Doppler survey designed to detect brown dwarf and giant planetary companions to a magnitude-limited sample of ultracool dwarfs. Using the NIRSPEC spectrograph on the Keck II telescope, we obtained approximately 600 radial velocity (RV) measurements over a period of six years of a sample of 59 late-M and L dwarfs spanning spectral types M8/L0 to L6. A subsample of 46 of our targets has been observed on three or more epochs. We rely on telluric CH 4 absorption features in Earth's atmosphere as a simultaneous wavelength reference and exploit the rich set of CO absorption features found in the K-band spectra of cool stars and brown dwarfs to measure RVs and projected rotational velocities. For a bright, slowly rotating M dwarf standard we demonstrate an RV precision of 50 m s -1 and for slowly rotating L dwarfs we achieve a typical RV precision of approximately 200 m s -1 . This precision is sufficient for the detection of close-in giant planetary companions to mid-L dwarfs as well as more equal mass spectroscopic binary systems with small separations (a +0.7 -0.6 Gyr, similar to that of nearby sun-like stars. We simulate the efficiency with which we detect spectroscopic binaries and find that the rate of tight (a +8.6 -1.6 %, consistent with recent estimates in the literature of a tight binary fraction of 3%-4%.

Nucleosynthesis in cold white dwarf explosions

International Nuclear Information System (INIS)

Canal, R.; Hernanz, M.

1986-01-01

Type I supernovae (SNI) are generally thought to be the main contributors to the galactic nucleosynthesis of iron-peak elements and their yields of intermediate-mass elements may also be important. We concentrate here upon a different class of models, based on the explosion of cold, massive, partially solid white dwarfs. We show that such white dwarfs must be relatively frequent among SNI progenitors and how their hydrodynamics upon ignition is very different from that of hotter, fluid white dwarfs. The implications for nucleosynthesis are briefly discussed and some preliminary results are presented

White dwarf models of supernovae and cataclysmic variables

International Nuclear Information System (INIS)

Nomoto, K.; Hashimoto, M.

1986-01-01

If the accreting white dwarf increases its mass to the Chandrasekhar mass, it will either explode as a Type I supernova or collapse to form a neutron star. In fact, there is a good agreement between the exploding white dwarf model for Type I supernovae and observations. We describe various types of evolution of accreting white dwarfs as a function of binary parameters (i.e,. composition, mass, and age of the white dwarf, its companion star, and mass accretion rate), and discuss the conditions for the precursors of exploding or collapsing white dwarfs, and their relevance to cataclysmic variables. Particular attention is given to helium star cataclysmics which might be the precursors of some Type I supernovae or ultrashort period x-ray binaries. Finally we present new evolutionary calculations using the updated nuclear reaction rates for the formation of O+Ne+Mg white dwarfs, and discuss the composition structure and their relevance to the model for neon novae. 61 refs., 14 figs

Is EG 50 a White or Strange Dwarf?

Science.gov (United States)

Hajyan, G. S.; Vartanyan, Yu. L.

2017-12-01

The time dependences of the luminosity of a white dwarf and four strange dwarfs with masses of 0.5 M (the mass of the white dwarf EG 50 with a surface temperature of 2.1·104 K) are determined taking neutrino energy losses into account. It was assumed that these configurations radiate only at the expense of thermal energy reserves. It is shown that the sources of thermal energy owing to nonequilibrium b-processes and the phenomenon of crystallization of electron-nuclear matter are insignificant in determining the cooling time of white and strange dwarfs with masses of 0.5 M⨀. It is shown that in this approximation the time dependences of the luminosity of white and strange dwarfs with masses of 0.5 M⨀ differ significantly only for surface temperatures TR≥7·104 K, so it is impossible to determine whether EG 50 is a white or strange dwarf based on the cooling time.

White dwarf evolution - Cradle-to-grave constraints via pulsation

Science.gov (United States)

Kawaler, Steven D.

1990-01-01

White dwarf evolution, particularly in the early phases, is not very strongly constrained by observation. Fortunately, white dwarfs undergo nonradial pulsation in three distinct regions of the H-R diagram. These pulsations provide accurate masses, surface compositional structure and rotation velocities, and help constrain other important physical properties. We demonstrate the application of the tools of stellar seismology to white dwarf evolution using the hot white dwarf star PG 1159-035 and the cool DAV (or ZZ Ceti) stars as examples. From pulsation studies, significant challenges to the theory of white dwarf evolution emerge.

Characterization of the N-terminal segment used by the barley yellow dwarf virus movement protein to promote interaction with the nuclear membrane of host plant cells.

Science.gov (United States)

Dennison, Sarah Rachel; Harris, Frederick; Brandenburg, Klaus; Phoenix, David Andrew

2007-11-01

The barley yellow dwarf virus movement protein (BYDV-MP) requires its N-terminal sequence to promote the transport of viral RNA into the nuclear compartment of host plant cells. Here, graphical analysis predicts that this sequence would form a membrane interactive amphiphilic alpha-helix. Confirming this prediction, NT1, a peptide homologue of the BYDV-MP N-terminal sequence, was found to be alpha-helical (65%) in the presence of vesicles mimics of the nuclear membrane. The peptide increased the fluidity of these nuclear membrane mimics (rise in wavenumber of circa 0.5-1.0 cm(-1)) and induced surface pressure changes of 2 mN m(-1) in lipid monolayers with corresponding compositions. Taken with isotherm analysis these results suggest that BYDV-MP forms an N-terminal amphiphilic alpha-helix, which partitions into the nuclear membrane primarily through thermodynamically stable associations with the membrane lipid headgroup region. We speculate that these associations may play a role in targeting of the nuclear membrane by BYDM-MP.

Searching for chemical signatures of brown dwarf formation

Science.gov (United States)

Maldonado, J.; Villaver, E.

2017-06-01

Context. Recent studies have shown that close-in brown dwarfs in the mass range 35-55 MJup are almost depleted as companions to stars, suggesting that objects with masses above and below this gap might have different formation mechanisms. Aims: We aim to test whether stars harbouring massive brown dwarfs and stars with low-mass brown dwarfs show any chemical peculiarity that could be related to different formation processes. Methods: Our methodology is based on the analysis of high-resolution échelle spectra (R 57 000) from 2-3 m class telescopes. We determine the fundamental stellar parameters, as well as individual abundances of C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, and Zn for a large sample of stars known to have a substellar companion in the brown dwarf regime. The sample is divided into stars hosting massive and low-mass brown dwarfs. Following previous works, a threshold of 42.5 MJup was considered. The metallicity and abundance trends of the two subsamples are compared and set in the context of current models of planetary and brown dwarf formation. Results: Our results confirm that stars with brown dwarf companions do not follow the well-established gas-giant planet metallicity correlation seen in main-sequence planet hosts. Stars harbouring massive brown dwarfs show similar metallicity and abundance distribution as stars without known planets or with low-mass planets. We find a tendency of stars harbouring less-massive brown dwarfs of having slightly higher metallicity, [XFe/Fe] values, and abundances of Sc II, Mn I, and Ni I than the stars having the massive brown dwarfs. The data suggest, as previously reported, that massive and low-mass brown dwarfs might present differences in period and eccentricity. Conclusions: We find evidence of a non-metallicity dependent mechanism for the formation of massive brown dwarfs. Our results agree with a scenario in which massive brown dwarfs are formed as stars. At high metallicities, the core

A low-temperature companion to a white dwarf star

Science.gov (United States)

Becklin, E. E.; Zuckerman, B.

1988-01-01

An infrared object located about 120 AU from the white dwarf GD165 has been discovered. With the exception of the possible brown dwarf companion to Giclas 29-38 reported last year, the companion to GD165 is the coolest (2100 K) dwarf star ever reported and, according to some theoretical models, it should be a substellar brown dwarf with a mass between 0.06 and 0.08 solar mass. These results, together with newly discovered low-mass stellar companions to white dwarfs, change the investigation of very low-mass stars from the study of a few chance objects to that of a statistical distribution. In particular, it appears that very low-mass stars and perhaps even brown dwarfs could be quite common in the Galaxy.

Passion Fruit Chlorotic Mottle Virus: Molecular Characterization of a New Divergent Geminivirus in Brazil.

Science.gov (United States)

Fontenele, Rafaela S; Abreu, Rayane A; Lamas, Natalia S; Alves-Freitas, Dione M T; Vidal, Andreza H; Poppiel, Raul R; Melo, Fernando L; Lacorte, Cristiano; Martin, Darren P; Campos, Magnolia A; Varsani, Arvind; Ribeiro, Simone G

2018-04-02

Brazil is one of the major passion fruit producers worldwide. Viral diseases are among the most important constraints for passion fruit production. Here we identify and characterize a new passion fruit infecting-virus belonging to the family Geminiviridae : passion fruit chlorotic mottle virus (PCMoV). PCMoV is a divergent geminivirus unlike previously characterized passion fruit-infecting geminiviruses that belonged to the genus Begomovirus . Among the presently known geminiviruses, it is most closely related to, and shares ~62% genome-wide identity with citrus chlorotic dwarf associated virus (CCDaV) and camelia chlorotic dwarf associated virus (CaCDaV). The 3743 nt PCMoV genome encodes a capsid protein (CP) and replication-associated protein (Rep) that respectively share 56 and 60% amino acid identity with those encoded by CaCDaV. The CPs of PCMoV, CCDaV, and CaCDaV cluster with those of begomovirus whereas their Reps with those of becurtoviruses. Hence, these viruses likely represent a lineage of recombinant begomo-like and becurto-like ancestral viruses. Furthermore, PCMoV, CCDaV, and CaCDaV genomes are ~12-30% larger than monopartite geminiviruses and this is primarily due to the encoded movement protein (MP; 891-921 nt) and this MP is most closely related to that encoded by the DNA-B component of bipartite begomoviruses. Hence, PCMoV, CCDaV, and CaCDaV lineage of viruses may represent molecules in an intermediary step in the evolution of bipartite begomoviruses (~5.3 kb) from monopartite geminiviruses (~2.7-3 kb). An infectious clone of PCMoV systemically infected Nicotiana benthamina , Arabidopsis thaliana , and Passiflora edulis .

The Living with a Red Dwarf / Goldiloks Program: The Activity-Rotation-Age Relationships of M and K Dwarfs

Science.gov (United States)

Engle, Scott; Guinan, Edward Francis

2018-01-01

Over the past several years, the database of M dwarfs with determined ages has continually expanded, allowing us to furnish Activity-Rotation-Age Relationships as part of the Living with a Red Dwarf program. We have now begun to expand this successful program to also cover K dwarfs - the Goldiloks program. Both M and K dwarfs suffer from the same limitation - due to their long lifetimes and very slow nuclear evolution, the best method for determining ages for a large number of M and K dwarf targets is through “magnetic tracers” such as X-UV activity levels and stellar rotation rates. We report on the current results of our relationships: deriving photometric rotation rates; gathering X-UV measures with HST, IUE Chandra and XMM (both proposed by us, and archival); and assessing their impacts on our understanding of the evolutions and habitability of these stellar types.We gratefully acknowledge the support from NSF/RUI Grant AST 1009903, Chandra Grant GO-13200633, HST Grants GO-12124X and GO-13020X.

Space distribution and physical properties of cool dwarf stars

International Nuclear Information System (INIS)

Staller, R.F.A.

1979-01-01

A new study of the space density of red dwarfs based on a sample of red dwarfs in a field of 238 square degrees towards the South Galactic Pole is presented. A blink survey using red and blue copies of Mount Palomar Sky Survey plates of a six square degrees field centered on the South Galactic Pole was performed and the results (approximately 2500 red objects) and the discussion of these results are presented. The time that elapsed before a black dwarf becomes invisible is estimated and is suggested that low-velocity red dwarfs could be explained by contracting black dwarfs. Based on theoretical considerations it can be shown that the existence of a large number of low-velocity stars is in serious conflict with criteria for the stability of the galactic disk. It is shown that if one also takes into account all generations of black dwarfs that are already invisible and therfore old, the mean velocity of all black dwarfs is much higher so that there is no conflict with theory. Luminosity functions of red and black dwarfs in several photometric passbands are calculated. (Auth.)

A possible magnetic DA white dwarf

International Nuclear Information System (INIS)

Wickramasinghe, D.T.; Bessell, M.S.

1976-01-01

The spectrum of a peculiar southern white dwarf suspect BPM 25114 is described. A possible magnetic interpretation suggests a DA white dwarf with a field of about 10 7 gauss. The star appears to be both a spectrum variable and perhaps light variable

Long-lived ames dwarf mice are resistant to chemical stressors.

Science.gov (United States)

Bokov, Alex F; Lindsey, Merry L; Khodr, Christina; Sabia, Marian R; Richardson, Arlan

2009-08-01

To probe the connection between longevity and stress resistance, we compared the sensitivity of Ames long-lived dwarf mice and control littermates with paraquat, diquat, and dobutamine. In young adult animals, 95% of male and 39% of female controls died after paraquat administration, but no dwarf animals died. When the experiment was repeated at an older age or a higher dosage of paraquat, dwarf mice still showed greater resistance. Dwarf mice also were more resistant to diquat; 80% of male and 60% of female controls died compared with 40% and 20% of dwarf mice, despite greater sensitivity of dwarf liver to diquat. Dwarf mice were also less sensitive to dobutamine-induced cardiac stress and had lower levels of liver and lung F(2)-isoprostanes. This is the first direct in vivo evidence that long-lived Ames dwarf mice have enhanced resistance to chemical insult, particularly oxidative stressors.

Sweating the small stuff: simulating dwarf galaxies, ultra-faint dwarf galaxies, and their own tiny satellites

Science.gov (United States)

Wheeler, Coral; Oñorbe, Jose; Bullock, James S.; Boylan-Kolchin, Michael; Elbert, Oliver D.; Garrison-Kimmel, Shea; Hopkins, Philip F.; Kereš, Dušan

2015-10-01

We present Feedback in Realistic Environment (FIRE)/GIZMO hydrodynamic zoom-in simulations of isolated dark matter haloes, two each at the mass of classical dwarf galaxies (Mvir ≃ 1010 M⊙) and ultra-faint galaxies (Mvir ≃ 109 M⊙), and with two feedback implementations. The resulting central galaxies lie on an extrapolated abundance matching relation from M⋆ ≃ 106 to 104 M⊙ without a break. Every host is filled with subhaloes, many of which form stars. Each of our dwarfs with M⋆ ≃ 106 M⊙ has 1-2 well-resolved satellites with M⋆ = 3-200 × 103 M⊙. Even our isolated ultra-faint galaxies have star-forming subhaloes. If this is representative, dwarf galaxies throughout the Universe should commonly host tiny satellite galaxies of their own. We combine our results with the Exploring the Local Volume in Simulations (ELVIS) simulations to show that targeting ˜ 50 kpc regions around nearby isolated dwarfs could increase the chances of discovering ultra-faint galaxies by ˜35 per cent compared to random pointings, and specifically identify the region around the Phoenix dwarf galaxy as a good potential target. The well-resolved ultra-faint galaxies in our simulations (M⋆ ≃ 3-30 × 103 M⊙) form within Mpeak ≃ 0.5-3 × 109 M⊙ haloes. Each has a uniformly ancient stellar population ( > 10 Gyr) owing to reionization-related quenching. More massive systems, in contrast, all have late-time star formation. Our results suggest that Mhalo ≃ 5 × 109 M⊙ is a probable dividing line between haloes hosting reionization `fossils' and those hosting dwarfs that can continue to form stars in isolation after reionization.

THE BROWN DWARF KINEMATICS PROJECT (BDKP). IV. RADIAL VELOCITIES OF 85 LATE-M AND L DWARFS WITH MagE

Energy Technology Data Exchange (ETDEWEB)

Burgasser, Adam J. [Center for Astrophysics and Space Science, University of California San Diego, La Jolla, CA 92093 (United States); Logsdon, Sarah E. [Department of Physics and Astronomy, UCLA, 430 Portola Plaza, Box 951547, Los Angeles, CA 90095-1547 (United States); Gagné, Jonathan [Institute for Research on Exoplanets (iREx), Université de Montréal, Département de Physique, C.P. 6128 Succ. Centre-ville, Montréal, QC H3C 3J7 (Canada); Bochanski, John J. [Rider University, 2083 Lawrenceville Road, Lawrenceville, NJ 08648 (United States); Faherty, Jaqueline K. [Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015 (United States); West, Andrew A. [Department of Astronomy, Boston University, 725 Commonwealth Avenue Boston, MA 02215 (United States); Mamajek, Eric E. [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627 (United States); Schmidt, Sarah J. [Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States); Cruz, Kelle L., E-mail: aburgasser@ucsd.edu [Department of Astrophysics, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10034 (United States)

2015-09-15

Radial velocity measurements are presented for 85 late M- and L-type very low-mass stars and brown dwarfs obtained with the Magellan Echellette spectrograph. Targets primarily have distances within 20 pc of the Sun, with more distant sources selected for their unusual spectral energy distributions. We achieved precisions of 2–3 km s{sup −1}, and combined these with astrometric and spectrophotometric data to calculate UVW velocities. Most are members of the thin disk of the Galaxy, and velocity dispersions indicate a mean age of 5.2 ± 0.2 Gyr for sources within 20 pc. We find signficantly different kinematic ages between late-M dwarfs (4.0 ± 0.2 Gyr) and L dwarfs (6.5 ± 0.4 Gyr) in our sample that are contrary to predictions from prior simulations. This difference appears to be driven by a dispersed population of unusually blue L dwarfs which may be more prevalent in our local volume-limited sample than in deeper magnitude-limited surveys. The L dwarfs exhibit an asymmetric U velocity distribution with a net inward flow, similar to gradients recently detected in local stellar samples. Simulations incorporating brown dwarf evolution and Galactic orbital dynamics are unable to reproduce the velocity asymmetry, suggesting non-axisymmetric perturbations or two distinct L dwarf populations. We also find the L dwarfs to have a kinematic age-activity correlation similar to more massive stars. We identify several sources with low surface gravities, and two new substellar candidate members of nearby young moving groups: the astrometric binary DENIS J08230313–4912012AB, a low-probability member of the β Pictoris Moving Group; and 2MASS J15104786–2818174, a moderate-probability member of the 30–50 Myr Argus Association.

The Effects of Ram-pressure Stripping and Supernova Winds on the Tidal Stirring of Disky Dwarfs: Enhanced Transformation into Dwarf Spheroidals

Science.gov (United States)

Kazantzidis, Stelios; Mayer, Lucio; Callegari, Simone; Dotti, Massimo; Moustakas, Leonidas A.

2017-02-01

A conclusive model for the formation of dwarf spheroidal (dSph) galaxies still remains elusive. Owing to their proximity to the massive spirals Milky Way (MW) and M31, various environmental processes have been invoked to explain their origin. In this context, the tidal stirring model postulates that interactions with MW-sized hosts can transform rotationally supported dwarfs, resembling present-day dwarf irregular (dIrr) galaxies, into systems with the kinematic and structural properties of dSphs. Using N-body+SPH simulations, we investigate the dependence of this transformation mechanism on the gas fraction, f gas, in the disk of the progenitor dwarf. Our numerical experiments incorporate for the first time the combined effects of radiative cooling, ram-pressure stripping, star formation, supernova (SN) winds, and a cosmic UV background. For a given orbit inside the primary galaxy, rotationally supported dwarfs with gas fractions akin to those of observed dIrrs (f gas ≳ 0.5), demonstrate a substantially enhanced likelihood and efficiency of transformation into dSphs relative to their collisionless (f gas = 0) counterparts. We argue that the combination of ram-pressure stripping and SN winds causes the gas-rich dwarfs to respond more impulsively to tides, augmenting their transformation. When f gas ≳ 0.5, disky dwarfs on previously unfavorable low-eccentricity or large-pericenter orbits are still able to transform. On the widest orbits, the transformation is incomplete; the dwarfs retain significant rotational support, a relatively flat shape, and some gas, naturally resembling transition-type systems. We conclude that tidal stirring constitutes a prevalent evolutionary mechanism for shaping the structure of dwarf galaxies within the currently favored CDM cosmological paradigm.

The Effects of Ram-pressure Stripping and Supernova Winds on the Tidal Stirring of Disky Dwarfs: Enhanced Transformation into Dwarf Spheroidals

Energy Technology Data Exchange (ETDEWEB)

Kazantzidis, Stelios [Section of Astrophysics, Astronomy and Mechanics, Department of Physics, National and Kapodistrian University of Athens, 15784 Zografos, Athens (Greece); Mayer, Lucio [Center for Theoretical Astrophysics and Cosmology, Institute for Computational Science, University of Zürich, CH-8057 Zürich (Switzerland); Callegari, Simone [Anthropology Institute and Museum, University of Zürich, CH-8057 Zürich (Switzerland); Dotti, Massimo [Università degli Studi di Milano-Bicocca, Piazza della Scienza 3, I-20126 Milano (Italy); Moustakas, Leonidas A., E-mail: skazantzidis@phys.uoa.gr [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)

2017-02-10

A conclusive model for the formation of dwarf spheroidal (dSph) galaxies still remains elusive. Owing to their proximity to the massive spirals Milky Way (MW) and M31, various environmental processes have been invoked to explain their origin. In this context, the tidal stirring model postulates that interactions with MW-sized hosts can transform rotationally supported dwarfs, resembling present-day dwarf irregular (dIrr) galaxies, into systems with the kinematic and structural properties of dSphs. Using N -body+SPH simulations, we investigate the dependence of this transformation mechanism on the gas fraction, f {sub gas}, in the disk of the progenitor dwarf. Our numerical experiments incorporate for the first time the combined effects of radiative cooling, ram-pressure stripping, star formation, supernova (SN) winds, and a cosmic UV background. For a given orbit inside the primary galaxy, rotationally supported dwarfs with gas fractions akin to those of observed dIrrs ( f {sub gas} ≳ 0.5), demonstrate a substantially enhanced likelihood and efficiency of transformation into dSphs relative to their collisionless ( f {sub gas} = 0) counterparts. We argue that the combination of ram-pressure stripping and SN winds causes the gas-rich dwarfs to respond more impulsively to tides, augmenting their transformation. When f {sub gas} ≳ 0.5, disky dwarfs on previously unfavorable low-eccentricity or large-pericenter orbits are still able to transform. On the widest orbits, the transformation is incomplete; the dwarfs retain significant rotational support, a relatively flat shape, and some gas, naturally resembling transition-type systems. We conclude that tidal stirring constitutes a prevalent evolutionary mechanism for shaping the structure of dwarf galaxies within the currently favored CDM cosmological paradigm.

A multiwavelength study of superoutbursts in dwarf novae

International Nuclear Information System (INIS)

Woerd, H.J. van der.

1987-01-01

Dwarf novae are stellar systems consisting of two stars which orbit around each other within a few hours. In dwarf novae one of the stars, which is a bit smaller and less massive than our sun, loses matter to a very compact and degenerated star: a white dwarf. This white dwarf has nearly the same mass as our sun but its radius is about a hundred times smaller. The process of mass transport was studied on the basis of observations with the Exosat-satelite (European X-ray Observatory satelite). 397 refs.; 50 figs.; 21 tabs

White dwarf evolution - Cradle-to-grave constraints via pulsation

International Nuclear Information System (INIS)

Kawaler, S.D.

1990-01-01

White dwarf evolution, particularly in the early phases, is not very strongly constrained by observation. Fortunately, white dwarfs undergo nonradial pulsation in three distinct regions of the H-R diagram. These pulsations provide accurate masses, surface compositional structure and rotation velocities, and help constrain other important physical properties. We demonstrate the application of the tools of stellar seismology to white dwarf evolution using the hot white dwarf star PG 1159-035 and the cool DAV (or ZZ Ceti) stars as examples. From pulsation studies, significant challenges to the theory of white dwarf evolution emerge. 44 refs

IUE spectrophotometry of the DA4 primary in the short-period white dwarf-red dwarf spectroscopic binary Case 1

Science.gov (United States)

Sion, E. M.; Guinan, E. F.; Wesemael, F.

1984-01-01

Low-resolution ultraviolet International Ultraviolet Explorer spectra of the DA white dwarf Case 1 are presented. The spectra show the presence of the 1400 A feature, already discovered in several other DA stars, and of a shallower trough in the 1550-1700 A range. A model atmosphere analysis of the ultraviolet energy distribution of the Ly-alpha red wing yields T(e) = 13,000 + or - 500 K. Possible interpretations of the 1400 A feature are reviewed. Case 1 is the coolest white dwarf found in a short-period, detached white dwarf-red dwarf binary, and its cooling time is consistent with estimates of the efficiency of angular momentum removal mechanisms in the phases subsequent to common envelope binary evolution.

Conditions for accretion-induced collapse of white dwarfs

International Nuclear Information System (INIS)

Nomoto, Kenichi; Kondo, Yoji

1991-01-01

Recent discovery of an unexpectedly large number of low-mass binary pulsars (LMBPs) in globular clusters has instigated active discussions on the evolutionary origin of binary pulsars. Prompted by the possibility that at least some of LMBPs originate from accretion-induced collapse (AIC) of white dwarfs, a reexamination is conducted as to whether or not AIC occurs for the new models of O + Ne + Mg white dwarfs and solid C + O white dwarfs that can ignite explosive nuclear burning at significantly lower central densities than in the previous models. Even with low critical densities, AIC is still much more likely than explosion for both types of white dwarfs. Possible regions for AIC are presented in a diagram of mass accretion rate vs initial mass of the white dwarfs. 42 refs

Tidal Dwarf Galaxies and Missing Baryons

Directory of Open Access Journals (Sweden)

Frederic Bournaud

2010-01-01

Full Text Available Tidal dwarf galaxies form during the interaction, collision, or merger of massive spiral galaxies. They can resemble “normal” dwarf galaxies in terms of mass, size, and become dwarf satellites orbiting around their massive progenitor. They nevertheless keep some signatures from their origin, making them interesting targets for cosmological studies. In particular, they should be free from dark matter from a spheroidal halo. Flat rotation curves and high dynamical masses may then indicate the presence of an unseen component, and constrain the properties of the “missing baryons,” known to exist but not directly observed. The number of dwarf galaxies in the Universe is another cosmological problem for which it is important to ascertain if tidal dwarf galaxies formed frequently at high redshift, when the merger rate was high, and many of them survived until today. In this paper, “dark matter” is used to refer to the nonbaryonic matter, mostly located in large dark halos, that is, CDM in the standard paradigm, and “missing baryons” or “dark baryons” is used to refer to the baryons known to exist but hardly observed at redshift zero, and are a baryonic dark component that is additional to “dark matter”.

White dwarf stars with carbon atmospheres.

Science.gov (United States)

Dufour, P; Liebert, J; Fontaine, G; Behara, N

2007-11-22

White dwarfs represent the endpoint of stellar evolution for stars with initial masses between approximately 0.07 and 8-10, where is the mass of the Sun (more massive stars end their life as either black holes or neutron stars). The theory of stellar evolution predicts that the majority of white dwarfs have a core made of carbon and oxygen, which itself is surrounded by a helium layer and, for approximately 80 per cent of known white dwarfs, by an additional hydrogen layer. All white dwarfs therefore have been traditionally found to belong to one of two categories: those with a hydrogen-rich atmosphere (the DA spectral type) and those with a helium-rich atmosphere (the non-DAs). Here we report the discovery of several white dwarfs with atmospheres primarily composed of carbon, with little or no trace of hydrogen or helium. Our analysis shows that the atmospheric parameters found for these stars do not fit satisfactorily in any of the currently known theories of post-asymptotic giant branch evolution, although these objects might be the cooler counterpart of the unique and extensively studied PG 1159 star H1504+65 (refs 4-7). These stars, together with H1504+65, might accordingly form a new evolutionary sequence that follows the asymptotic giant branch.

HUBBLE SPACE TELESCOPE IMAGING AND SPECTRAL ANALYSIS OF TWO BROWN DWARF BINARIES AT THE L DWARF/T DWARF TRANSITION

International Nuclear Information System (INIS)

Burgasser, Adam J.; Bardalez-Gagliuffi, Daniella C.; Gizis, John E.

2011-01-01

We present a detailed examination of the brown dwarf multiples 2MASS J08503593+1057156 and 2MASS J17281150+3948593, both suspected of harboring components that straddle the L dwarf/T dwarf transition. Resolved photometry from Hubble Space Telescope/NICMOS shows opposite trends in the relative colors of the components, with the secondary of 2MASS J0850+1057 being redder than its primary, while that of 2MASS J1728+3948 is bluer. We determine near-infrared component types by matching combined-light, near-infrared spectral data to binary templates, with component spectra scaled to resolved NICMOS and K p photometry. Combinations of L7 + L6 for 2MASS J0850+1057 and L5 + L6.5 for 2MASS J1728+3948 are inferred. Remarkably, the primary of 2MASS J0850+1057 appears to have a later-type classification compared to its secondary, despite being 0.8-1.2 mag brighter in the near-infrared, while the primary of 2MASS J1728+3948 is unusually early for its combined-light optical classification. Comparison to absolute magnitude/spectral type trends also distinguishes these components, with 2MASS J0850+1057A being ∼1 mag brighter and 2MASS J1728+3948A ∼ 0.5 mag fainter than equivalently classified field counterparts. We deduce that thick condensate clouds are likely responsible for the unusual properties of 2MASS J1728+3948A, while 2MASS J0850+1057A is either an inflated young brown dwarf or a tight unresolved binary, making it potentially part of a wide, low-mass, hierarchical quintuple system.

Genetic Segregation Analysis of a Rapeseed Dwarf Mutant

International Nuclear Information System (INIS)

Xiang, G.; Yu, S.; Zhang, T.; Zhao, J.; Lei, S.; Du, C.

2016-01-01

Dwarf resources in Brassica napus are very important for developing high-yield cultivars through dwarf-type and lodging-resistant breeding. However, few dwarf varieties have been available for this species. Here, we reported a new rapeseed dwarf mutant GRC1157, which exhibits obvious phenotypic variations on dwarf. Six generations (P /sub 1/, P/sub 1/, F/sub 1/, F/sub 1/, B/sub 1/, and B/sub 1/) were produced from a cross between dwarf mutant GRC1157 and an elite tall-type line XR16 to analyze genetic inheritances of plant height (PH), numbers of the 1st valid branch (VBN), main inflorescence length (MIL), pod numbers per main inflorescence (MPN), pod length (PL) and seed numbers per pod (PSN) using the mixed major gene plus polygene inheritance model. The genetic analysis shows different traits were controlled by different inheritance models: PH and PL by two pairs of additive-dominant-epistatic major genes plus additive-dominant-epistatic polygenes, MPN and PSN by two-pair additive-dominant-epistatic major genes plus additive-dominant polygenes, MIL by two-pair additive-dominant-epistatic major genes and VBN by one-pair additive-dominant major genes plus additive-dominant-epistatic polygenes. Furthermore, positive correlations between PH and some other traits were observed, suggesting that some traits may be co-regulated by several linkage or same loci/genes. In addition, high heritability (40.35-93.7 percent) were found for five traits (except VBN) in different segregating generations, indicating these traits were mainly affected by hereditary factors and suitable for early artificial selection. In sum, the dwarf mutant GRC1157 can serve as a valuable resource for rapeseed dwarf breeding and the genetic analysis in this study provided a foundation for further mapping and cloning dwarf genes in mutant GRC1157. (author)

CCD photometry of apparent dwarf galaxies in Fornax

International Nuclear Information System (INIS)

Phillipps, S.; Grimley, P.L.; Disney, M.J.; Cawson, M.G.M.; Kibblewhite, E.J.

1986-01-01

Blue and red CCD surface photometry of two apparent dwarf galaxies in the Fornax cluster region is presented. Luminosity profiles are derived and their form discussed. The fainter galaxy resembles an archetypal diffuse dwarf elliptical but the brighter of the pair is either an unusual red dwarf or a background galaxy in chance juxtaposition. (author)

A BROWN DWARF CENSUS FROM THE SIMP SURVEY

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Robert, Jasmin; Gagné, Jonathan; Artigau, Étienne; Lafrenière, David; Nadeau, Daniel; Doyon, René; Malo, Lison; Albert, Loïc; Simard, Corinne [Département de physique and Observatoire du Mont-Mégantic, Université de Montréal, Montréal, QC H3C 3J7 (Canada); Gagliuffi, Daniella C. Bardalez; Burgasser, Adam J., E-mail: jasmin@astro.umontreal.ca [Center for Astrophysics and Space Sciences, University of California San Diego, 9500 Gilman Dr., Mail Code 0424, La Jolla, CA 92093 (United States)

2016-10-20

We have conducted a near-infrared (NIR) proper motion survey, the Sondage Infrarouge de Mouvement Propre, in order to discover field ultracool dwarfs (UCD) in the solar neighborhood. The survey was conducted by imaging ∼28% of the sky with the Caméra PAnoramique Proche-InfraRouge both in the southern hemisphere at the Cerro Tololo Inter-American Observatory 1.5 m telescope, and in the northern hemisphere at the Observatoire du Mont-Mégantic 1.6 m telescope and comparing the source positions from these observations with the Two Micron All-Sky Survey Point Source Catalog (2MASS PSC). Additional color criteria were used to further discriminate unwanted astrophysical sources. We present the results of an NIR spectroscopic follow-up of 169 M, L, and T dwarfs. Among the sources discovered are 2 young field brown dwarfs, 6 unusually red M and L dwarfs, 25 unusually blue M and L dwarfs, 2 candidate unresolved L+T binaries, and 24 peculiar UCDs. Additionally, we add 9 L/T transition dwarfs (L6–T4.5) to the already known objects.

A BROWN DWARF CENSUS FROM THE SIMP SURVEY

International Nuclear Information System (INIS)

Robert, Jasmin; Gagné, Jonathan; Artigau, Étienne; Lafrenière, David; Nadeau, Daniel; Doyon, René; Malo, Lison; Albert, Loïc; Simard, Corinne; Gagliuffi, Daniella C. Bardalez; Burgasser, Adam J.

2016-01-01

We have conducted a near-infrared (NIR) proper motion survey, the Sondage Infrarouge de Mouvement Propre, in order to discover field ultracool dwarfs (UCD) in the solar neighborhood. The survey was conducted by imaging ∼28% of the sky with the Caméra PAnoramique Proche-InfraRouge both in the southern hemisphere at the Cerro Tololo Inter-American Observatory 1.5 m telescope, and in the northern hemisphere at the Observatoire du Mont-Mégantic 1.6 m telescope and comparing the source positions from these observations with the Two Micron All-Sky Survey Point Source Catalog (2MASS PSC). Additional color criteria were used to further discriminate unwanted astrophysical sources. We present the results of an NIR spectroscopic follow-up of 169 M, L, and T dwarfs. Among the sources discovered are 2 young field brown dwarfs, 6 unusually red M and L dwarfs, 25 unusually blue M and L dwarfs, 2 candidate unresolved L+T binaries, and 24 peculiar UCDs. Additionally, we add 9 L/T transition dwarfs (L6–T4.5) to the already known objects.

Dwarf Galaxies in the Chandra COSMOS Legacy Survey

Science.gov (United States)

Civano, Francesca Maria; Mezcua, Mar; Fabbiano, Giuseppina; Marchesi, Stefano; Suh, Hyewon; Volonteri, Marta; cyrille

2018-01-01

The existence of intermediate mass black holes (100 7. While detecting these seed black holes in the young Universe is observationally challenging, the nuclei of local dwarf galaxies are among the best places where to look for them as these galaxies resemble in mass and metallicity the first galaxies and they have not significantly grown through merger and accretion processes. We present a sample of 40 AGN in dwarf galaxies (107 0.5, our sample constitutes the highest-redshift discovery of AGN in dwarf galaxies. One of the dwarf galaxies is the least massive galaxy (M* = 6.6x107 Msun) found so far to host an active BH. We also present for the first time the evolution of the AGN fraction with stellar mass, X-ray luminosity, and redshift in dwarf galaxies out to z = 0.7, finding that it decreases with X-ray luminosity and stellar mass. Unlike massive galaxies, the AGN fraction is found to decrease with redshift, suggesting that AGN in dwarf galaxies evolve differently than those in high-mass galaxies.

Possible new class of dense white dwarfs

International Nuclear Information System (INIS)

Glendenning, N.K.; Kettner, C.; Weber, F.

1995-01-01

If the strange quark matter hypothesis is true, then a new class of white dwarfs can exist whose nuclear material in their deep interiors can have a density as high as the neutron drip density, a few hundred times the density in maximum-mass white dwarfs and 4x10 4 the density in dwarfs of mass, M∼0.6 M circle-dot . Their masses fall in the approximate range 10 -4 to 1 M circle-dot . They are stable against acoustical modes of vibration. A strange quark core stabilizes these stars, which otherwise would have central densities that would place them in the unstable region of the sequence between white dwarfs and neutron stars. copyright 1995 American Institute of Physics

POPULATION PROPERTIES OF BROWN DWARF ANALOGS TO EXOPLANETS

International Nuclear Information System (INIS)

Faherty, Jacqueline K.; Gagne, Jonathan; Weinberger, Alycia; Riedel, Adric R.; Cruz, Kelle L.; Filippazzo, Joseph C.; Lambrides, Erini; Fica, Haley; Baldassare, Vivienne; Lemonier, Emily; Rice, Emily L.; Thorstensen, John R.; Tinney, C. G.

2016-01-01

We present a kinematic analysis of 152 low surface gravity M7-L8 dwarfs by adding 18 new parallaxes (including 10 for comparative field objects), 38 new radial velocities, and 19 new proper motions. We also add low- or moderate-resolution near-infrared spectra for 43 sources confirming their low surface gravity features. Among the full sample, we find 39 objects to be high-likelihood or new bona fide members of nearby moving groups, 92 objects to be ambiguous members and 21 objects that are non-members. Using this age-calibrated sample, we investigate trends in gravity classification, photometric color, absolute magnitude, color–magnitude, luminosity, and effective temperature. We find that gravity classification and photometric color clearly separate 5–130 Myr sources from >3 Gyr field objects, but they do not correlate one to one with the narrower 5–130 Myr age range. Sources with the same spectral subtype in the same group have systematically redder colors, but they are distributed between 1 and 4 σ from the field sequences and the most extreme outlier switches between intermediate- and low-gravity sources either confirmed in a group or not. The absolute magnitudes of low-gravity sources from the J band through W 3 show a flux redistribution when compared to equivalently typed field brown dwarfs that is correlated with spectral subtype. Low-gravity, late-type L dwarfs are fainter at J than the field sequence but brighter by W 3. Low-gravity M dwarfs are >1 mag brighter than field dwarfs in all bands from J through W 3. Clouds, which are a far more dominant opacity source for L dwarfs, are the likely cause. On color–magnitude diagrams, the latest-type, low-gravity L dwarfs drive the elbow of the L/T transition up to 1 mag redder and 1 mag fainter than field dwarfs at M J but are consistent with or brighter than the elbow at M W1 and M W2 . We conclude that low-gravity dwarfs carry an extreme version of the cloud conditions of field objects to lower

Infrared spectrum of an extremely cool white-dwarf star

Science.gov (United States)

Hodgkin; Oppenheimer; Hambly; Jameson; Smartt; Steele

2000-01-06

White dwarfs are the remnant cores of stars that initially had masses of less than 8 solar masses. They cool gradually over billions of years, and have been suggested to make up much of the 'dark matter' in the halo of the Milky Way. But extremely cool white dwarfs have proved difficult to detect, owing to both their faintness and their anticipated similarity in colour to other classes of dwarf stars. Recent improved models indicate that white dwarfs are much more blue than previously supposed, suggesting that the earlier searches may have been looking for the wrong kinds of objects. Here we report an infrared spectrum of an extremely cool white dwarf that is consistent with the new models. We determine the star's temperature to be 3,500 +/- 200 K, making it the coolest known white dwarf. The kinematics of this star indicate that it is in the halo of the Milky Way, and the density of such objects implied by the serendipitous discovery of this star is consistent with white dwarfs dominating the dark matter in the halo.

Identifying Likely Disk-hosting M dwarfs with Disk Detective

Science.gov (United States)

Silverberg, Steven; Wisniewski, John; Kuchner, Marc J.; Disk Detective Collaboration

2018-01-01

M dwarfs are critical targets for exoplanet searches. Debris disks often provide key information as to the formation and evolution of planetary systems around higher-mass stars, alongside the planet themselves. However, less than 300 M dwarf debris disks are known, despite M dwarfs making up 70% of the local neighborhood. The Disk Detective citizen science project has identified over 6000 new potential disk host stars from the AllWISE catalog over the past three years. Here, we present preliminary results of our search for new disk-hosting M dwarfs in the survey. Based on near-infrared color cuts and fitting stellar models to photometry, we have identified over 500 potential new M dwarf disk hosts, nearly doubling the known number of such systems. In this talk, we present our methodology, and outline our ongoing work to confirm systems as M dwarf disks.

The Effects of Ram-pressure Stripping and Supernova Winds on the Tidal Stirring of Disky Dwarfs: Enhanced Transformation into Dwarf Spheroidals

International Nuclear Information System (INIS)

Kazantzidis, Stelios; Mayer, Lucio; Callegari, Simone; Dotti, Massimo; Moustakas, Leonidas A.

2017-01-01

A conclusive model for the formation of dwarf spheroidal (dSph) galaxies still remains elusive. Owing to their proximity to the massive spirals Milky Way (MW) and M31, various environmental processes have been invoked to explain their origin. In this context, the tidal stirring model postulates that interactions with MW-sized hosts can transform rotationally supported dwarfs, resembling present-day dwarf irregular (dIrr) galaxies, into systems with the kinematic and structural properties of dSphs. Using N -body+SPH simulations, we investigate the dependence of this transformation mechanism on the gas fraction, f _g_a_s, in the disk of the progenitor dwarf. Our numerical experiments incorporate for the first time the combined effects of radiative cooling, ram-pressure stripping, star formation, supernova (SN) winds, and a cosmic UV background. For a given orbit inside the primary galaxy, rotationally supported dwarfs with gas fractions akin to those of observed dIrrs ( f _g_a_s ≳ 0.5), demonstrate a substantially enhanced likelihood and efficiency of transformation into dSphs relative to their collisionless ( f _g_a_s = 0) counterparts. We argue that the combination of ram-pressure stripping and SN winds causes the gas-rich dwarfs to respond more impulsively to tides, augmenting their transformation. When f _g_a_s ≳ 0.5, disky dwarfs on previously unfavorable low-eccentricity or large-pericenter orbits are still able to transform. On the widest orbits, the transformation is incomplete; the dwarfs retain significant rotational support, a relatively flat shape, and some gas, naturally resembling transition-type systems. We conclude that tidal stirring constitutes a prevalent evolutionary mechanism for shaping the structure of dwarf galaxies within the currently favored CDM cosmological paradigm.

Interaction Research on the Antiviral Molecule Dufulin Targeting on Southern Rice Black Streaked Dwarf Virus P9-1 Nonstructural Protein

Directory of Open Access Journals (Sweden)

Zhenchao Wang

2015-03-01

Full Text Available ern rice black streaked dwarf virus (SRBSDV causes severe harm to rice production. Unfortunately, studies on effective antiviral drugs against SRBSDV and interaction mechanism of antiviral molecule targeting on SRBSDV have not been reported. This study found dufulin (DFL, an ideal anti-SRBSDV molecule, and investigated the interactions of DFL targeting on the nonstructural protein P9-1. The biological sequence information and bonding characterization of DFL to four kinds of P9-1 protein were described with fluorescence titration (FT and microscale thermophoresis (MST assays. The sequence analysis indicated that P9-1 had highly-conserved C- and N-terminal amino acid residues and a hypervariable region that differed from 131 aa to 160 aa. Consequently, wild-type (WT-His-P9-1, 23 C-terminal residues truncated (TR-ΔC23-His-P9-1, 6 N-terminal residues truncated (TR-ΔN6-His-P9-1, and Ser138 site-directed (MU-138-His-P9-1 mutant proteins were expressed. The FT and MST assay results indicated that DFL bounded to WT-His-P9-1 with micromole affinity and the 23 C-terminal amino acids were the potential targeting site. This system, which combines a complete sequence analysis, mutant protein expression, and binding action evaluating system, could further advance the understanding of the interaction abilities between antiviral drugs and their targets.

THE WHITE DWARF AGE OF NGC 2477

International Nuclear Information System (INIS)

Jeffery, Elizabeth J.; Von Hippel, Ted; DeGennaro, Steven; Jefferys, William H.; Van Dyk, David A.; Stein, Nathan

2011-01-01

We present deep photometric observations of the open cluster NGC 2477 using HST/WFPC2. By identifying seven cluster white dwarf candidates, we present an analysis of the white dwarf age of this cluster, using both the traditional method of fitting isochrones to the white dwarf cooling sequence, and by employing a new Bayesian statistical technique that has been developed by our group. This new method performs an objective, simultaneous model fit of the cluster and stellar parameters (namely, age, metallicity, distance, reddening, as well as individual stellar masses, mass ratios, and cluster membership) to the photometry. Based on this analysis, we measure a white dwarf age of 1.035 ± 0.054 ± 0.087 Gyr (uncertainties represent the goodness of model fits and discrepancy among models, respectively) in good agreement with the cluster's main-sequence turnoff age. This work is part of our ongoing work to calibrate main-sequence turnoff and white dwarf ages using open clusters, and to improve the precision of cluster ages to the ∼5% level.

Rapid detection of fifteen known soybean viruses by dot-immunobinding assay.

Science.gov (United States)

Ali, Akhtar

2017-11-01

A dot-immunobinding assay (DIBA) was optimized and used successfully for the rapid detection of 15 known viruses [Alfalfa mosaic virus (AMV), Bean pod mottle virus (BPMV), Bean yellow mosaic virus (BYMV), Cowpea mild mottle virus (CPMMV), Cowpea severe mosaic virus (CPSMV), Cucumber mosaic virus (CMV), Peanut mottle virus (PeMoV), Peanut stunt virus (PSV), Southern bean mosaic virus (SBMV), Soybean dwarf virus (SbDV), Soybean mosaic virus (SMV), Soybean vein necrosis virus (SVNV), Tobacco ringspot virus (TRSV), Tomato ringspot virus (ToRSV), and Tobacco streak virus (TSV)] infecting soybean plants in Oklahoma. More than 1000 leaf samples were collected in approximately 100 commercial soybean fields in 24 counties of Oklahoma, during the 2012-2013 growing seasons. All samples were tested by DIBA using polyclonal antibodies of the above 15 plant viruses. Thirteen viruses were detected, and 8 of them were reported for the first time in soybean crops of Oklahoma. The highest average incidence was recorded for PeMoV (13.5%) followed by SVNV (6.9%), TSV (6.4%), BYMV, (4.5%), and TRSV (3.9%), while the remaining seven viruses were detected in less than 2% of the samples tested. The DIBA was quick, and economical to screen more than 1000 samples against 15 known plant viruses in a very short time. Copyright © 2017 Elsevier B.V. All rights reserved.

Branes constrictions with White Dwarfs

International Nuclear Information System (INIS)

García-Aspeitia, Miguel A.

2015-01-01

We consider here a robust study of stellar dynamics for white dwarf stars with polytropic matter in the weak-field approximation using the Lane–Emden equation from the brane-world scenario. We also derive an analytical solution to the nonlocal energy density and show the behavior and sensitivity of these stars to the presence of extra dimensions. Similarly, we analyze stability and compactness, in order to show whether it is possible to agree with the conventional wisdom of white dwarfs dynamics. Our results predict an average value of the brane tension of <λ>≳84.818 MeV 4 , with a standard deviation σ≃82.021 MeV 4 , which comes from a sample of dwarf stars, being weaker than other astrophysical observations but remaining higher than cosmological results provided by nucleosynthesis among others

Topics in white dwarf astrophysics

International Nuclear Information System (INIS)

Hintzen, P.M.N.

1975-01-01

This study was designed to investigate the apparent deficiency, compared to theoretical predictions, of cool degenerate stars. Two approaches to the problem were employed: a spectroscopic survey designed to identify red degenerates, and a model atmospheres study of the spectroscopic and photometric differences between red dwarfs and red degenerate stars. On computed atmospheric models for white dwarfs at the temperatures under investigation. Line profiles obtained from these models indicate that degenerate stars with T/sub e/ approximately 6000 0 K and depleted surface metals would be extremely difficult to identify spectroscopically. Their hydrogen and calcium line profiles would strongly resemble those of classical sub-dwarfs. Three apparently degenerate stars whose spectral features match our predictions have been identified. These results indicate that the existence of the previously postulated deficiency of red degenerate stars is uncertain

Variable Stars in the M31 Dwarf Spheroidal Companion Cassiopeia

Science.gov (United States)

Pritzl, Barton J.; Armandroff, T. E.; Jacoby, G. H.; Da Costa, G. S.

2007-12-01

Dwarf spheroidal galaxies show very diverse star formation histories. For the Galactic dwarf spheroidal galaxies, a correlation exists between Galactocentric distance and the prominence of intermediate-age ( 2 - 10 Gyr) populations. To test whether this correlation exists for the M31 dwarf spheroidal galaxies, we observed the Cassiopeia (And VII) dwarf galaxy, which is one of the most distant M31 dwarf spheroidal galaxies. We will present the results of a variable star search using HST/ACS data, along with a preliminary color-magnitude diagram. From the RR Lyrae stars we can obtain an independent distance and metallicity estimate for the dwarf galaxy. These results will be compared to those found for the other M31 dwarf spheroidal galaxies.This research is supported in part by NASA through grant number GO-11081.11 from the Space Telescope Science Institute.

ROBO-AO M DWARF MULTIPLICITY SURVEY

Science.gov (United States)

Lamman, Claire; Berta-Thompson, Zachory; Baranec, Christoph; Law, Nicholas; Schonhut, Jessica

2018-01-01

We analyzed over 7,000 observations from Robo-AO’s field M dwarf survey taken on the 2.1m Kitt Peak telescope. Results will help determine the multiplicity fraction of M dwarfs as a function of primary mass, which is a crucial step towards understanding their evolution and formation mechanics. Through its robotic, laser-guided, and automated system, the Robo-AO instrument has yielded the largest adaptive-optics M dwarf survey to date. I developed a graphical user interface to quickly analyze this data. Initial data analysis included assessing data quality, checking the result from Robo-AO’s automatic reduction pipeline, and determining existence as well as the relative position of companions through a visual inspection. This program can be applied to other datasets and was successfully tested by re-analyzing observations from a separate Robo-AO survey. Following the preliminary results from this data analysis tool, further observations were done with the Keck II telescope by using its NIRC2 imager to follow up on ten select targets for the existence and physical association of companions. After a conservative initial cut for quality, 356 companions were found within 4” of a primary star out of 2,746 high quality Robo-AO M dwarf observations, including four triple systems. We will present a preliminary estimate for the multiplicity rate of wide M dwarf companions after accounting for observation limitations and the completeness of our search. Future research will yield insights into low-mass stellar formation and provide a database of nearby M dwarf multiples that will potentially assist ongoing and future surveys for planets around these stars, such as the NASA TESS mission.

Rice black-streaked dwarf virus P6 self-interacts to form punctate, viroplasm-like structures in the cytoplasm and recruits viroplasm-associated protein P9-1

Directory of Open Access Journals (Sweden)

Yu Jialin

2011-01-01

Full Text Available Abstract Background Rice black-streaked dwarf virus (RBSDV, a member of the genus Fijivirus within the family Reoviridae, can infect several graminaceous plant species including rice, maize and wheat, and is transmitted by planthoppers. Although several RBSDV proteins have been studied in detail, functions of the nonstructural protein P6 are still largely unknown. Results In the current study, we employed yeast two-hybrid assays, bimolecular fluorescence complementation and subcellular localization experiments to show that P6 can self-interact to form punctate, cytoplasmic viroplasm-like structures (VLS when expressed alone in plant cells. The region from residues 395 to 659 is necessary for P6 self-interaction, whereas two polypeptides (residues 580-620 and 615-655 are involved in the subcellular localization of P6. Furthermore, P6 strongly interacts with the viroplasm-associated protein P9-1 and recruits P9-1 to localize in VLS. The P6 395-659 region is also important for the P6-P9-1 interaction, and deleting any region of P9-1 abolishes this heterologous interaction. Conclusions RBSDV P6 protein has an intrinsic ability to self-interact and forms VLS without other RBSDV proteins or RNAs. P6 recruits P9-1 to VLS by direct protein-protein interaction. This is the first report on the functionality of RBSDV P6 protein. P6 may be involved in the process of viroplasm nucleation and virus morphogenesis.

Molecular characterization of barley 3H semi-dwarf genes.

Directory of Open Access Journals (Sweden)

Haobing Li

Full Text Available The barley chromosome 3H accommodates many semi-dwarfing genes. To characterize these genes, the two-rowed semi-dwarf Chinese barley landrace 'TX9425' was crossed with the Australian barley variety 'Franklin' to generate a doubled haploid (DH population, and major QTLs controlling plant height have been identified in our previous study. The major QTL derived from 'TX9425' was targeted to investigate the allelism of the semi-dwarf gene uzu in barley. Twelve sets of near-isogenic lines and a large NILF2 fine mapping population segregating only for the dwarfing gene from 'TX9425' were developed. The semi-dwarfing gene in 'TX9425' was located within a 2.8 cM region close to the centromere on chromosome 3H by fine mapping. Molecular cloning and sequence analyses showed that the 'TX9425'-derived allele contained a single nucleotide substitution from A to G at position 2612 of the HvBRI1 gene. This was apparently the same mutation as that reported in six-rowed uzu barley. Markers co-segregating with the QTL were developed from the sequence of the HvBRI1 gene and were validated in the 'TX9425'/'Franklin' DH population. The other major dwarfing QTL derived from the Franklin variety was distally located on chromosome 3HL and co-segregated with the sdw1 diagnostic marker hv20ox2. A third dwarfing gene, expressed only in winter-sown trials, was identified and located on chromosome 3HS. The effects and interactions of these dwarfing genes under different growing conditions are discussed. These results improve our understanding of the genetic mechanisms controlling semi-dwarf stature in barley and provide diagnostic markers for the selection of semi-dwarfness in barley breeding programs.

Thermochemical modelling of brown dwarf discs

NARCIS (Netherlands)

Greenwood, A. J.; Kamp, I.; Waters, L. B. F. M.; Woitke, P.; Thi, W.-F.; Rab, Ch.; Aresu, G.; Spaans, M.

The physical properties of brown dwarf discs, in terms of their shapes and sizes, are still largely unexplored by observations. ALMA has by far the best capabilities to observe these discs in sub-mm CO lines and dust continuum, while also spatially resolving some discs. To what extent brown dwarf

White dwarfs in cataclysmic variables

International Nuclear Information System (INIS)

Sion, E.M.

1987-01-01

The physical properties and evolutionary state of the underlying white dwarfs in CVs are explored. Observations of 25 white dwarfs with effective temperature upper limits of 9000-75,000 K are discussed. Correlations between effective temperature, orbital period, accretion rate, and CV type with respect to the CV period gap are considered. Quasi-static and hydrodynamic evolutionary models are used to explain the surface temperature/luminosity distribution ratios. 42 references

Dusty Dwarfs Galaxies Occulting A Bright Background Spiral

Science.gov (United States)

Holwerda, Benne

2017-08-01

The role of dust in shaping the spectral energy distributions of low mass disk galaxies remains poorly understood. Recent results from the Herschel Space Observatory imply that dwarf galaxies contain large amounts of cool (T 20K) dust, coupled with very modest optical extinctions. These seemingly contradictory conclusions may be resolved if dwarfs harbor a variety of dust geometries, e.g., dust at larger galactocentric radii or in quiescent dark clumps. We propose HST observations of six truly occulting dwarf galaxies drawn from the Galaxy Zoo catalog of silhouetted galaxy pairs. Confirmed, true occulting dwarfs are rare as most low-mass disks in overlap are either close satellites or do not have a confirmed redshift. Dwarf occulters are the key to determining the spatial extent of dust, the small scale structure introduced by turbulence, and the prevailing dust attenuation law. The recent spectroscopic confirmation of bona-fide low mass occulting dwarfs offers an opportunity to map dust in these with HST. What is the role of dust in the SED of these dwarf disk galaxies? With shorter feedback scales, how does star-formation affect their morphology and dust composition, as revealed from their attenuation curve? The resolution of HST allows us to map the dust disks down to the fine scale structure of molecular clouds and multi-wavelength imaging maps the attenuation curve and hence dust composition in these disks. We therefore ask for 2 orbits on each of 6 dwarf galaxies in F275W, F475W, F606W, F814W and F125W to map dust from UV to NIR to constrain the attenuation curve.

Physiological values of some blood indicators in selected dwarf rabbit breeds

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V. Šimek

2017-03-01

Full Text Available The aim of the present study was to evaluate the effect of breed on haematological and biochemical indicators in 3 dwarf rabbit breeds. In the experiment, 30 sexually intact dwarf rabbit females aged 6 mo were used. With the sole exception of white blood cells and haematocrit value, breed had the most significant effect on the majority of haematological indicators monitored. The red blood cell count was higher in the Dwarf Lop compared to the Netherland Dwarf (+1.91×1012 cells/L; P<0.05 and also the Teddy Dwarf (+1.32×1012 cells/L; P<0.05. For haemoglobin concentration, a higher value was found in the Netherland Dwarf than in the Teddy Dwarf (+39.29 g/L; P<0.05 and the Dwarf Lop (+26.36 g/L; P<0.05. For erythrocytic indicators, the highest values of mean corpuscular volume, mean corpuscular haemoglobin and mean corpuscular haemoglobin concentration were found in the Netherland Dwarf. The breed had a significant effect on the urea and potassium values. A higher value of urea was recorded in the Dwarf Lop compared to the Teddy Dwarf (+1.56 mmol/L; P<0.05. For potassium, a higher value was found in the Netherland Dwarf compared to the Teddy Dwarf (+0.85 mmol/L; P<0.05. In addition, a significantly positive correlation (P<0.05 was found between the live weight of dwarf females and values of haematocrit (0.49, albumin (0.54, alanine aminotransferase (0.51, and aspartate aminotransferase (0.41, while a significantly negative correlation (P<0.05 was found between their live weight and values of triacylglycerols (–0.44, alkaline phosphatase (–0.38 and inorganic phosphorus (–0.52.

LOW CO LUMINOSITIES IN DWARF GALAXIES

International Nuclear Information System (INIS)

Schruba, Andreas; Walter, Fabian; Sandstrom, Karin; Leroy, Adam K.; Bigiel, Frank; Brinks, Elias; De Blok, W. J. G.; Kramer, Carsten; Rosolowsky, Erik; Schuster, Karl; Usero, Antonio; Weiss, Axel; Wiesemeyer, Helmut

2012-01-01

We present maps of 12 COJ = 2-1 emission covering the entire star-forming disks of 16 nearby dwarf galaxies observed by the IRAM HERACLES survey. The data have 13'' angular resolution, ∼250 pc at our average distance of D = 4 Mpc, and sample the galaxies by 10-1000 resolution elements. We apply stacking techniques to perform the first sensitive search for CO emission in dwarf galaxies outside the Local Group ranging from individual lines of sight, stacking over IR-bright regions of embedded star formation, and stacking over the entire galaxy. We detect five galaxies in CO with total CO luminosities of L CO2-1 = (3-28) × 10 6 K km s –1 pc 2 . The other 11 galaxies remain undetected in CO even in the stacked images and have L CO2-1 ∼ 6 K km s –1 pc 2 . We combine our sample of dwarf galaxies with a large sample of spiral galaxies from the literature to study scaling relations of L CO with M B and metallicity. We find that dwarf galaxies with metallicities of Z ≈ 1/2-1/10 Z ☉ have L CO of 2-4 orders of magnitude smaller than massive spiral galaxies and that their L CO per unit L B is 1-2 orders of magnitude smaller. A comparison with tracers of star formation (FUV and 24 μm) shows that L CO per unit star formation rate (SFR) is 1-2 orders of magnitude smaller in dwarf galaxies. One possible interpretation is that dwarf galaxies form stars much more efficiently: we argue that the low L CO /SFR ratio is due to the fact that the CO-to-H 2 conversion factor, α CO , changes significantly in low-metallicity environments. Assuming that a constant H 2 depletion time of τ dep = 1.8 Gyr holds in dwarf galaxies (as found for a large sample of nearby spirals) implies α CO values for dwarf galaxies with Z ≈ 1/2-1/10 Z ☉ that are more than one order of magnitude higher than those found in solar metallicity spiral galaxies. Such a significant increase of α CO at low metallicity is consistent with previous studies, in particular those of Local Group dwarf

General Relativistic Calculations for White Dwarf Stars

OpenAIRE

Mathew, Arun; Nandy, Malay K.

2014-01-01

The mass-radius relations for white dwarf stars are investigated by solving the Newtonian as well as Tolman-Oppenheimer-Volkoff (TOV) equations for hydrostatic equilibrium assuming the electron gas to be non-interacting. We find that the Newtonian limiting mass of $1.4562M_\\odot$ is modified to $1.4166M_\\odot$ in the general relativistic case for $^4_2$He (and $^{12}_{\\ 6}$C) white dwarf stars. Using the same general relativistic treatment, the critical mass for $^{56}_{26}$Fe white dwarf is ...

A STUDY OF THE DIVERSE T DWARF POPULATION REVEALED BY WISE

International Nuclear Information System (INIS)

Mace, Gregory N.; Wright, Edward L.; McLean, Ian S.; Davy Kirkpatrick, J.; Gelino, Christopher R.; Griffith, Roger L.; Mix, Katholeen; Beichman, Charles A.; Lowrance, Patrick J.; Cushing, Michael C.; Skrutskie, Michael F.; Marsh, Kenneth A.; Eisenhardt, Peter R.; Thompson, Maggie A.; Bailey, Vanessa; Hinz, Philip M.; Knox, Russell P.; Bloom, Joshua S.; Burgasser, Adam J.; Fortney, Jonathan J.

2013-01-01

We report the discovery of 87 new T dwarfs uncovered with the Wide-field Infrared Survey Explorer (WISE) and 3 brown dwarfs with extremely red near-infrared colors that exhibit characteristics of both L and T dwarfs. Two of the new T dwarfs are likely binaries with L7 ± 1 primaries and mid-type T secondaries. In addition, our follow-up program has confirmed 10 previously identified T dwarfs and 4 photometrically selected L and T dwarf candidates in the literature. This sample, along with the previous WISE discoveries, triples the number of known brown dwarfs with spectral types later than T5. Using the WISE All-Sky Source Catalog we present updated color-color and color-type diagrams for all the WISE-discovered T and Y dwarfs. Near-infrared spectra of the new discoveries are presented along with spectral classifications. To accommodate later T dwarfs we have modified the integrated flux method of determining spectral indices to instead use the median flux. Furthermore, a newly defined J-narrow index differentiates the early-type Y dwarfs from late-type T dwarfs based on the J-band continuum slope. The K/J indices for this expanded sample show that 32% of late-type T dwarfs have suppressed K-band flux and are blue relative to the spectral standards, while only 11% are redder than the standards. Comparison of the Y/J and K/J index to models suggests diverse atmospheric conditions and supports the possible re-emergence of clouds after the L/T transition. We also discuss peculiar brown dwarfs and candidates that were found not to be substellar, including two young stellar objects and two active galactic nuclei. The substantial increase in the number of known late-type T dwarfs provides a population that will be used to test models of cold atmospheres and star formation. The coolest WISE-discovered brown dwarfs are the closest of their type and will remain the only sample of their kind for many years to come.

Branes constrictions with White Dwarfs

Energy Technology Data Exchange (ETDEWEB)

García-Aspeitia, Miguel A., E-mail: aspeitia@fisica.uaz.edu.mx [Consejo Nacional de Ciencia y Tecnología, Av, Insurgentes Sur 1582, Colonia Crédito Constructor, Del. Benito Juárez, C.P. 03940, Mexico, D.F. (Mexico); Unidad Académica de Física, Universidad Autónoma de Zacatecas, Calzada Solidaridad esquina con Paseo a la Bufa S/N, C.P. 98060, Zacatecas (Mexico)

2015-11-06

We consider here a robust study of stellar dynamics for white dwarf stars with polytropic matter in the weak-field approximation using the Lane–Emden equation from the brane-world scenario. We also derive an analytical solution to the nonlocal energy density and show the behavior and sensitivity of these stars to the presence of extra dimensions. Similarly, we analyze stability and compactness, in order to show whether it is possible to agree with the conventional wisdom of white dwarfs dynamics. Our results predict an average value of the brane tension of <λ>≳84.818 MeV{sup 4}, with a standard deviation σ≃82.021 MeV{sup 4}, which comes from a sample of dwarf stars, being weaker than other astrophysical observations but remaining higher than cosmological results provided by nucleosynthesis among others.

Branes constrictions with White Dwarfs

Energy Technology Data Exchange (ETDEWEB)

Garcia-Aspeitia, Miguel A. [Consejo Nacional de Ciencia y Tecnologia, Mexico (Mexico); Unidad Academica de Fisica, Universidad Autonoma de Zacatecas (Mexico)

2015-11-15

We consider here a robust study of stellar dynamics for white dwarf stars with polytropic matter in the weak-field approximation using the Lane-Emden equation from the brane-world scenario. We also derive an analytical solution to the nonlocal energy density and show the behavior and sensitivity of these stars to the presence of extra dimensions. Similarly, we analyze stability and compactness, in order to show whether it is possible to agree with the conventional wisdom of white dwarfs dynamics. Our results predict an average value of the brane tension of left angle λ right angle >or similar 84.818 MeV{sup 4}, with a standard deviation σ ≅ 82.021 MeV{sup 4}, which comes from a sample of dwarf stars, being weaker than other astrophysical observations but remaining higher than cosmological results provided by nucleosynthesis among others. (orig.)

Benchmark ultra-cool dwarfs in widely separated binary systems

Directory of Open Access Journals (Sweden)

Jones H.R.A.

2011-07-01

Full Text Available Ultra-cool dwarfs as wide companions to subgiants, giants, white dwarfs and main sequence stars can be very good benchmark objects, for which we can infer physical properties with minimal reference to theoretical models, through association with the primary stars. We have searched for benchmark ultra-cool dwarfs in widely separated binary systems using SDSS, UKIDSS, and 2MASS. We then estimate spectral types using SDSS spectroscopy and multi-band colors, place constraints on distance, and perform proper motions calculations for all candidates which have sufficient epoch baseline coverage. Analysis of the proper motion and distance constraints show that eight of our ultra-cool dwarfs are members of widely separated binary systems. Another L3.5 dwarf, SDSS 0832, is shown to be a companion to the bright K3 giant η Cancri. Such primaries can provide age and metallicity constraints for any companion objects, yielding excellent benchmark objects. This is the first wide ultra-cool dwarf + giant binary system identified.

Implications of the dwarfs spheroidal galaxy mass-metallicity relation

International Nuclear Information System (INIS)

Smith, G.H.

1985-01-01

The properties of the mass-metallicity relation among dwarf spheroidal galaxies are discussed in terms of a model which assumes that the internal chemical evolution of the dwarf spheroidals was promoted by supernova activity. The model can be used to explain the observed dwarf spheroidal mass-metallicity relation assuming the present mass of these systems M sub s is proportional to their initial masses M as M sub s varies according to a power-law index of exp 7/4. It is inferred from the power-law dependence of M on the proto-cloud radius that the most massive dwarf spheroids were formed from the densest clouds. The observed slope of the mass-metallicity relation for dwarf spheroidal galaxies is found to be significantly different from theoretical estimates of this slope for elliptical galaxies. It is suggested that the difference may imply that spheroidal dwarfs and elliptical galaxies had different formation histories, confirming Kormendy's (1985) observations of differences in the brightness and luminosity trends. 54 references

Genetic and agronomic evaluation of induced semi-dwarf mutants of rice

International Nuclear Information System (INIS)

Rutger, J.N.

1984-01-01

Induced semi-dwarf mutants have played an important role in California's rapid shift from nearly all tall rice varieties in 1978 to nearly all semi-dwarf varieties at present. In 1981 over half of the California rice area was planted with semi-dwarf varieties carrying the induced mutant semi-dwarfing gene sd 1 , while much of the other half was planted to a variety deriving its semi-dwarfism from IR8. The sd 1 mutant is allelic to the major semi-dwarfing gene in DGWG and IR8. Current objectives are to determine the inheritance of new semi-dwarf mutants, including allelism tests with sd 1 , and to evaluate the agronomic potential of nonallelic sources and of double-dwarfs. To date semi-dwarf mutants from 10 varieties have been partially or completely evaluated. At least three nonallelic semi-dwarfing genes, sd 1 , sd 2 , and sd 4 , have been described. Rather than attempt to determine all possible allelic relationships of new mutants, crosses are being made only to the reference sd 1 source, since sd 1 , still seems to be the most productive semi-dwarfing gene source. However, nonallelic semi-dwarf mutants in the varieties M5 and Labelle may be useful if genetic vulnerability from widespread usage of the sd 1 source becomes a problem. (author)

ON THE EVOLUTION OF MAGNETIC WHITE DWARFS

Energy Technology Data Exchange (ETDEWEB)

Tremblay, P.-E. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Fontaine, G.; Brassard, P. [Département de Physique, Université de Montréal, C. P. 6128, Succursale Centre-Ville, Montréal, QC H3C 3J7 (Canada); Freytag, B. [Department of Physics and Astronomy at Uppsala University, Regementsvägen 1, Box 516, SE-75120 Uppsala (Sweden); Steiner, O. [Kiepenheuer-Institut für Sonnenphysik, Schöneckstr. 6, D-79104 Freiburg (Germany); Ludwig, H.-G. [Zentrum für Astronomie der Universität Heidelberg, Landessternwarte, Königstuhl 12, D-69117 Heidelberg (Germany); Steffen, M. [Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, D-14482 Potsdam (Germany); Wedemeyer, S., E-mail: tremblay@stsci.edu [Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029 Blindern, NO-0315 Oslo (Norway)

2015-10-10

We present the first radiation magnetohydrodynamic simulations of the atmosphere of white dwarf stars. We demonstrate that convective energy transfer is seriously impeded by magnetic fields when the plasma-β parameter, the thermal-to-magnetic-pressure ratio, becomes smaller than unity. The critical field strength that inhibits convection in the photosphere of white dwarfs is in the range B = 1–50 kG, which is much smaller than the typical 1–1000 MG field strengths observed in magnetic white dwarfs, implying that these objects have radiative atmospheres. We have employed evolutionary models to study the cooling process of high-field magnetic white dwarfs, where convection is entirely suppressed during the full evolution (B ≳ 10 MG). We find that the inhibition of convection has no effect on cooling rates until the effective temperature (T{sub eff}) reaches a value of around 5500 K. In this regime, the standard convective sequences start to deviate from the ones without convection due to the convective coupling between the outer layers and the degenerate reservoir of thermal energy. Since no magnetic white dwarfs are currently known at the low temperatures where this coupling significantly changes the evolution, the effects of magnetism on cooling rates are not expected to be observed. This result contrasts with a recent suggestion that magnetic white dwarfs with T{sub eff} ≲ 10,000 K cool significantly slower than non-magnetic degenerates.

Dwarf mistletoes: Biology, pathology, and systematics

Science.gov (United States)

Frank G. Hawksworth; Delbert Wiens

1996-01-01

Arceuthobium (dwarf mistletoes), a well defined but morphologically reduced genus of the family Viscaceae, is parasitic on Pinaceae in the Old and New Worlds and on Cupressaceae in the Old World. Although conifer forests in many parts of the Northern Hemisphere are infested with dwarf mistletoes, those most commonly infested are in western North...

Sour and duke cherry viruses in South-West Europe

Directory of Open Access Journals (Sweden)

Rodrigo PÉREZ-SÁNCHEZ

2017-05-01

Full Text Available This study investigated the phytosanitary status of sour and duke cherry genetic resources in the Iberian Peninsula, and the incidence and leaf symptoms induced by the Prunus necrotic ringspot virus (PNRSV, Prune dwarf virus (PDV and Apple chlorotic leaf spot virus (ACLSV. Young leaf samples were taken from 204 sour and duke cherry trees belonging to ten cultivars, and were assayed by DAS-ELISA. Samples positive for any of the three viruses were also tested by RT-PCR. To associate the leaf symptoms with virus presence, 50 mature leaves from each infected tree were visually inspected during the summer. The ELISA and RT-PCR results indicated that 63% of the cherry trees were infected by at least one of these viruses. PNRSV occurred in all cultivars sampled and presented the highest infection rate (46%, followed by PDV (31% and ACLSV (6%. Many trees, (60 to 100%, were asymptomatic while harbouring single and mixed virus infections. The leaf symptoms associated with the viruses included chlorotic and dark brown necrotic ringspots on secondary veins and interveinal regions, for PNRSV, generalized chlorosis around the midveins, for PDV, chlorotic and reddish necrotic ringspots, for ACLSV, and generalized interveinal chlorosis, for mixed PNRSV and PDVinfections.

Perdas de água e solo por erosão hídrica em duas direções de semeadura de aveia e ervilhaca Water and soil losses through water erosion under oat and vetch sown in two directions

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Rodrigo Vieira Luciano

2009-06-01

acumuladas de solo (PS aumentaram com a lâmina (LC e a erosividade (EI30 acumulada das chuvas, entre os testes 1 e 4, segundo as equações: PS = 0,859(1-e-0,0059LC (R² = 0,99 e PS = 0,832(1-e-0,0004EI30 (R² = 0,99.The sowing direction influences soil surface roughness, which, combined with rainfall and other variables, e.g., canopy cover, affects soil water erosion. Using a rotating-boom rainfall simulator, five tests of simulated rainfall were applied to black oat (Avena strigosa, and vetch (Vicia sativa, at a constant intensity of 64 mm h-1, between August and November 2006, to assess water and soil loss in the following treatment: mechanized seeding of oats in downslope rows; mechanized seeding of oats along contour lines; mechanized seeding of vetch in downslope rows, and mechanized seeding of vetch along contour lines. The experiment was conducted in two replications on an Inceptisol, with a mean slope of 0.119 m m-1. The canopy cover was greater in oat than vetch until rainfall test 2 and higher in vetch in the tests 3 and 4, with no variation due to the sowing direction of the crops and increasing from the beginning to the end of the growth period. The time until the water started to run off was longer in the treatments with seeding along contour lines than downslope, in both crops; the maximum runoff rate along the contour lines was lower and the time until maximum runoff rate longer. The sediment concentration in runoff decreased over the rainfall tests; it was lower in oat than vetch, and 52 % lower in contour than downslope sowing. Soil loss decreased over the rainfall tests; these losses were 12 % lower in oat and 56 % lower in vetch contour than downslope sowing; the water loss had the same performance as soil loss, although with lower magnitudes. The accumulated soil losses increased with accumulated rain volume (VR and rain erosivity (EI30, between the first and fourth test, according to the equations: SL = 0.859 (1-e-0.0059VR (R² = 0.99 and SL = 0.832 (1

A dwarf wheat mutant is associated with increased drought ...

African Journals Online (AJOL)

... was significantly higher than Jingdong 6. Most of the s-dwarf seedlings survived in recovering experiement after water loss. The stalk of s-dwarf seedling also showed reduced gravitropism. This is the first report about a new dwarf wheat mutant associated with increased drought resistance and altered stalk gravitropism.

Ages of white dwarf-red subdwarf systems

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Hektor Monteiro

2006-01-01

Full Text Available We provide the first age estimates for two recently discovered white dwarf-red subdwarf systems, LHS 193AB and LHS 300AB. These systems provide a new opportunity for linking the reliable age estimates for the white dwarfs to the (measurable metallicities of the red subdwarfs. We have obtained precise photometry in the VJRKCIKCJH bands and spectroscopy covering from 6,000°A to 9,000°A (our spectral coveragefor the two new systems, as well as for a comparison white dwarfmain sequence red dwarf system, GJ 283 AB. Using model grids, we estimate the cooling age as well as temperature, surface gravity, mass, progenitor mass and total lifetimes of the white dwarfs. The results indicate that the two new systems are probably ancient thick disk objects with ages of at least 6-9 gigayears (Gyr.

Double Degenerates among DA white dwarfs

International Nuclear Information System (INIS)

Bragaglia, A.; Greggio, L.; Renzini, A.; D'odorico, S.

1990-01-01

The results of a spectroscopic survey of catalog white dwarfs in search of radial velocity variations indicative of a binary motion are reported. In a sample of 54 DA white dwarfs, one Double Degenerate (DD) system with a period of 1.15 days (the shortest period DD system yet discovered) is found. Two other excellent and two good DD candidates, and two white dwarf + red dwarf pairs were also found. If all the candidates should be confirmed, this would indicate a frequency of about 13 percent of interacting binaries in an unbiased sample of evolved stars, with a DD frequency of about 10 percent. These results suggest fairly large values for the common-envelope parameter alpha, implying that a source of energy other than orbital may be required to eject the envelope during common-envelope events. Finally, in combination with previous evidence our result implies that DDs with WD components of the DA variety are unlikely to be the precursors of Type I supernovae, but DDs with non-DA components remain very attractive candidates. 20 refs

Evaluation on selected dwarf and semidwarf mutants of upland rice

International Nuclear Information System (INIS)

Riyanti Sumanggono, A.M.

1984-01-01

Seratus malam local upland rice variety was irradiated with gamma-rays at doses of O.1, 0.2, 0.3, 0.4 and 0.5 kGy. Observation of radiation effect was carried out on root and shoot length of M 1 seedlings; plant height, panicle length and number of tiller and seed sterility in M 1 plants. Selection for dwarf and semi-dwarf characteristics were done in M 2 plants, and selected again in M 3 . Observation on radiation effect indicated that 'Seratus Malam' seems to be more resistant than the lowland rice varieties. Increasing doses of radiation caused increasing frequency of chlorophyll mutations as well as chlorophyll mutants. Whereas, selection of dwarf or semi-dwarf in M 2 plants seems that mutant and mutation frequencies decreased as the dose increased. Dose of 0.2 kGy was suitable for selection of dwarf or semi-dwarf plants. Plant height could be influenced by environmental condition. Many of the selected M 2 plants were not really dwarf or semi-dwarf mutants. M 3 evaluation of the selected M 2 plants was really beneficial in the mutant selection. (author)

Brown dwarfs in retrogradely precessing cataclysmic variables?

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Martin E.L.

2011-07-01

Full Text Available We compare Smoothed Particle Hydrodynamic simulations of retrogradely precessing accretion disks that have a white dwarf primary and a main sequence secondary with observational data and with theory on retrograde precession via tidal torques like those by the Moon and the Sun on the Earth [1, 2]. Assuming the primary does not accrete much of the mass lost from the secondary, we identify the theoretical low mass star/brown dwarf boundary. We find no observational candidates in our study that could qualify as brown dwarfs.

Binding constants of Southern rice black-streaked dwarf virus Coat Protein with ferulic acid derivatives

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Longlu Ran

2018-04-01

Full Text Available The data present binding constants between ferulic acid derivatives and the Coat Protein (P10 by fluorescence titration in this article, which is hosted in the research article entitled “Interaction Research on an Antiviral Molecule that Targets the Coat Protein of Southern rice black-streaked dwarf virus’’ (Ran et al., 2017 [1]. The data include fluorescence quenching spectrum, Stern–Volmer quenching constants, and binding parameters. In this article, a more comprehensive data interpretation and analysis is explained.

Population demographics for the federally endangered dwarf wedgemussel

Science.gov (United States)

Galbraith, Heather S.; Lellis, William A.; Cole, Jeffrey C.; Blakeslee, Carrie J.; St. John White, Barbara

2016-01-01

The dwarf wedgemussel, Alasmidonta heterodon, is a federally endangered freshwater mussel species inhabiting several Atlantic Slope rivers. Studies on population demographics of this species are necessary for status assessment and directing recovery efforts. We conducted qualitative and quantitative surveys for dwarf wedgemussel in the mainstem Delaware River and in four of its tributaries (Big Flat Brook, Little Flat Brook, Neversink River, and Paulinskill River). Population range, relative abundance, size, size structure, and sex ratio were quantified within each river. Total dwarf wedgemussel population size for the surveyed rivers in the Delaware Basin was estimated to be 14,432 individuals (90% confidence limits, 7,961-26,161). Our results suggest that the historically robust Neversink River population has declined, but that this population persists and substantial populations remain in other tributaries. Sex ratios were generally female-biased, and small individuals (Dwarf wedgemussel was most often found at the surface of the sediment (not buried below) in shallow quadrats (dwarf wedgemussel viability within the Delaware River Basin.

METALLICITY AND TEMPERATURE INDICATORS IN M DWARF K-BAND SPECTRA: TESTING NEW AND UPDATED CALIBRATIONS WITH OBSERVATIONS OF 133 SOLAR NEIGHBORHOOD M DWARFS

Energy Technology Data Exchange (ETDEWEB)

Rojas-Ayala, Barbara [Department of Astrophysics, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024 (United States); Covey, Kevin R.; Lloyd, James P. [Department of Astronomy, Cornell University, 122 Sciences Drive, Ithaca, NY 14853 (United States); Muirhead, Philip S., E-mail: babs@amnh.org [Department of Astronomy, California Institute of Technology, 1200 East California Boulevard, MC 249-17, Pasadena, CA 91125 (United States)

2012-04-01

We present K-band spectra for 133 nearby (d < 33 ps) M dwarfs, including 18 M dwarfs with reliable metallicity estimates (as inferred from an FGK type companion), 11 M dwarf planet hosts, more than 2/3 of the M dwarfs in the northern 8 pc sample, and several M dwarfs from the LSPM catalog. From these spectra, we measure equivalent widths of the Ca and Na lines, and a spectral index quantifying the absorption due to H{sub 2}O opacity (the H{sub 2}O-K2 index). Using empirical spectral type standards and synthetic models, we calibrate the H{sub 2}O-K2 index as an indicator of an M dwarf's spectral type and effective temperature. We also present a revised relationship that estimates the [Fe/H] and [M/H] metallicities of M dwarfs from their Na I, Ca I, and H{sub 2}O-K2 measurements. Comparisons to model atmosphere provide a qualitative validation of our approach, but also reveal an overall offset between the atomic line strengths predicted by models as compared to actual observations. Our metallicity estimates also reproduce expected correlations with Galactic space motions and H{alpha} emission line strengths, and return statistically identical metallicities for M dwarfs within a common multiple system. Finally, we find systematic residuals between our H{sub 2}O-based spectral types and those derived from optical spectral features with previously known sensitivity to stellar metallicity, such as TiO, and identify the CaH1 index as a promising optical index for diagnosing the metallicities of near-solar M dwarfs.

Simultaneous detection of four garlic viruses by multiplex reverse transcription PCR and their distribution in Indian garlic accessions.

Science.gov (United States)

Majumder, S; Baranwal, V K

2014-06-01

Indian garlic is infected with Onion yellow dwarf virus (OYDV), Shallot latent virus (SLV), Garlic common latent virus (GarCLV) and allexiviruses. Identity and distribution of garlic viruses in various garlic accessions from different geographical regions of India were investigated. OYDV and allexiviruses were observed in all the garlic accessions, while SLV and GarCLV were observed only in a few accessions. A multiplex reverse transcription (RT)-PCR method was developed for the simultaneous detection and identification of OYDV, SLV, GarCLV and Allexivirus infecting garlic accessions in India. This multiplex protocol standardized in this study will be useful in indexing of garlic viruses and production of virus free seed material. Copyright © 2014 Elsevier B.V. All rights reserved.

Global and photospheric physical parameters of active dwarf stars

International Nuclear Information System (INIS)

Pettersen, B.R.

1983-01-01

Physical parameters (temperature, luminosity, radius, mass and chemical abundance) of the photospheres of red dwarf flare stars and spotted stars are determined for quiescent conditions. The interrelations between these quantities are compared to the results of theoretical investigation for low mass stars. The evolutionary state of flare stars is discussed. Observational results from spectroscopic and photometric methods to determine the rotation of active dwarfs are reviewed. The possibilities of global oscillations in dwarf stars are considered and preliminary results of a photometric search for oscillation in red dwarf luminosities are presented. (orig.)

The mass dependence of dwarf satellite galaxy quenching

International Nuclear Information System (INIS)

Slater, Colin T.; Bell, Eric F.

2014-01-01

We combine observations of the Local Group with data from the NASA-Sloan Atlas to show the variation in the quenched fraction of satellite galaxies from low-mass dwarf spheroidals and dwarf irregulars to more massive dwarfs similar to the Magellanic Clouds. While almost all of the low-mass (M * ≲ 10 7 M ☉ ) dwarfs are quenched, at higher masses the quenched fraction decreases to approximately 40%-50%. This change in the quenched fraction is large and suggests a sudden change in the effectiveness of quenching that correlates with satellite mass. We combine this observation with models of satellite infall and ram pressure stripping to show that the low-mass satellites must quench within 1-2 Gyr of pericenter passage to maintain a high quenched fraction, but that many more massive dwarfs must continue to form stars today even though they likely fell into their host >5 Gyr ago. We also characterize how the susceptibility of dwarfs to ram pressure must vary as a function of mass if it is to account for the change in quenched fractions. Though neither model predicts the quenching effectiveness a priori, this modeling illustrates the physical requirements that the observed quenched fractions place on possible quenching mechanisms.

Robo-AO M Dwarf Multiplicity Survey

Science.gov (United States)

Lamman, Claire; Baranec, Christoph; Berta-Thompson, Zachory K.; Law, Nicholas M.; Ziegler, Carl; Schonhut-Stasik, Jessica

2018-06-01

We analyzed close to 7,000 observations from Robo-AO’s field M dwarf survey taken on the 2.1m Kitt Peak telescope. Results will help determine the total multiplicity fraction and multiplicity functions of M dwarfs, which are crucial steps towards understanding their evolution and formation mechanics. Through its robotic, laser-guided, and automated system, the Robo-AO instrument has yielded the largest adaptive-optics M dwarf survey to date. I developed a graphical user interface to quickly analyze this data. Initial data analysis included assessing data quality, checking the result from Robo-AO’s automatic reduction pipeline, and determining existence as well as the relative position of companions through a visual inspection. This program can be applied to other datasets and was successfully tested by re-analyzing observations from a separate Robo-AO survey. After a conservative initial cut for quality, over 350 companions were found within 4” of a primary star out of 2,746 high quality Robo-AO M dwarf observations, including four triple systems. Further observations were done with the Keck II telescope by using its NIRC2 imager to follow up on ten select targets for the existence and physical association of companions. Future research will yield insights into low-mass stellar formation and provide a database of nearby M dwarf multiples that will potentially assist ongoing and future surveys for planets around these stars, such as the NASA TESS mission.

Serendipitous discovery of a dwarf Nova in the Kepler field near the G dwarf KIC 5438845

International Nuclear Information System (INIS)

Brown, Alexander; Ayres, Thomas R.; Neff, James E.; Wells, Mark A.; Kowalski, Adam; Hawley, Suzanne; Berdyugina, Svetlana; Harper, Graham M.; Korhonen, Heidi; Piskunov, Nikolai; Saar, Steven; Walkowicz, Lucianne

2015-01-01

The Kepler satellite provides a unique window into stellar temporal variability by observing a wide variety of stars with multi-year, near-continuous, high precision, optical photometric time series. While most Kepler targets are faint stars with poorly known physical properties, many unexpected discoveries should result from a long photometric survey of such a large area of sky. During our Kepler Guest Observer programs that monitored late-type stars for starspot and flaring variability, we discovered a previously unknown dwarf nova that lies within a few arcseconds of the mid-G dwarf star KIC 5438845. This dwarf nova underwent nine outbursts over a 4 year time span. The two largest outbursts lasted ∼17–18 days and show strong modulations with a 110.8 minute period and a declining amplitude during the outburst decay phase. These properties are characteristic of an SU UMa-type cataclysmic variable. By analogy with other dwarf nova light curves, we associate the 110.8 minute (1.847 hr) period with the superhump period, close to but slightly longer than the orbital period of the binary. No precursor outbursts are seen before the super-outbursts and the overall super-outburst morphology corresponds to Osaki and Meyer “Case B” outbursts, which are initiated when the outer edge of the disk reaches the tidal truncation radius. “Case B” outbursts are rare within the Kepler light curves of dwarf novae. The dwarf nova is undergoing relatively slow mass transfer, as evidenced by the long intervals between outbursts, but the mass transfer rate appears to be steady, because the smaller “normal” outbursts show a strong correlation between the integrated outburst energy and the elapsed time since the previous outburst. At super-outburst maximum the system was at V ∼ 18, but in quiescence it is fainter than V ∼ 22, which will make any detailed quiescent follow-up of this system difficult.

K2 Ultracool Dwarfs Survey. III. White Light Flares Are Ubiquitous in M6-L0 Dwarfs

Science.gov (United States)

Paudel, Rishi R.; Gizis, John E.; Mullan, D. J.; Schmidt, Sarah J.; Burgasser, Adam J.; Williams, Peter K. G.; Berger, Edo

2018-05-01

We report the white light flare rates for 10 ultracool dwarfs using Kepler K2 short-cadence data. Among our sample stars, two have spectral type M6, three are M7, three are M8, and two are L0. Most of our targets are old low-mass stars. We identify a total of 283 flares in all of the stars in our sample, with Kepler energies in the range log E Kp ∼ (29–33.5) erg. Using the maximum-likelihood method of line fitting, we find that the flare frequency distribution (FFD) for each star in our sample follows a power law with slope ‑α in the range ‑(1.3–2.0). We find that cooler objects tend to have shallower slopes. For some of our targets, the FFD follows either a broken power law, or a power law with an exponential cutoff. For the L0 dwarf 2MASS J12321827-0951502, we find a very shallow slope (‑α = ‑1.3) in the Kepler energy range (0.82–130) × 1030 erg: this L0 dwarf has flare rates which are comparable to those of high-energy flares in stars of earlier spectral types. In addition, we report photometry of two superflares: one on the L0 dwarf 2MASS J12321827-0951502 and another on the M7 dwarf 2MASS J08352366+1029318. In the case of 2MASS J12321827-0951502, we report a flare brightening by a factor of ∼144 relative to the quiescent photospheric level. Likewise, for 2MASS J08352366+1029318, we report a flare brightening by a factor of ∼60 relative to the quiescent photospheric level. These two superflares have bolometric (ultraviolet/optical/infrared) energies 3.6 × 1033 erg and 8.9 × 1033 erg respectively, while the full width half maximum timescales are very short, ∼2 min. We find that the M8 star TRAPPIST-1 is more active than the M8.5 dwarf 2M03264453+1919309, but less active than another M8 dwarf (2M12215066-0843197).

Deep Sequencing Data and Infectivity Assays Indicate that Chickpea Chlorotic Dwarf Virus is the Etiological Agent of the “Hard Fruit Syndrome” of Watermelon

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Takoua Zaagueri

2017-10-01

Full Text Available Chickpea chlorotic dwarf virus (CpCDV, a polyphagous mastrevirus, family Geminiviridae, has been recently linked to the onset of the “hard fruit syndrome” of watermelon, first described in Tunisia, that makes fruits unmarketable due to the presence of white hard portions in the flesh, chlorotic mottling on the rind, and an unpleasant taste. To investigate the etiological agent of this disease, total RNA extracted from symptomatic watermelon fruits was subjected to small RNA sequencing through next generation sequencing (NGS techniques. Data obtained showed the presence of CpCDV and two other viral species. However, following validation through polymerase chain reaction (PCR, CpCDV was the only viral species consistently detected in all samples. Watermelon seedlings were then challenged by an agroinfectious CpCDV clone; several plants proved to be CpCDV-infected, and were able to produce fruits. CpCDV infected and replicated in watermelon fruits and leaves, leading to abnormality in fruits and in seed production, similar to those described in field. These results indicate that CpCDV is the etiological agent of the “hard fruit syndrome” of watermelon.

Genesis of magnetic fields in isolated white dwarfs

Science.gov (United States)

Briggs, Gordon P.; Ferrario, Lilia; Tout, Christopher A.; Wickramasinghe, Dayal T.

2018-05-01

A dynamo mechanism driven by differential rotation when stars merge has been proposed to explain the presence of strong fields in certain classes of magnetic stars. In the case of the high field magnetic white dwarfs (HFMWDs), the site of the differential rotation has been variously thought to be the common envelope, the hot outer regions of a merged degenerate core or an accretion disc formed by a tidally disrupted companion that is subsequently accreted by a degenerate core. We have shown previously that the observed incidence of magnetism and the mass distribution in HFMWDs are consistent with the hypothesis that they are the result of merging binaries during common envelope evolution. Here we calculate the magnetic field strengths generated by common envelope interactions for synthetic populations using a simple prescription for the generation of fields and find that the observed magnetic field distribution is also consistent with the stellar merging hypothesis. We use the Kolmogorov-Smirnov test to study the correlation between the calculated and the observed field strengths and find that it is consistent for low envelope ejection efficiency. We also suggest that field generation by the plunging of a giant gaseous planet on to a white dwarf may explain why magnetism among cool white dwarfs (including DZ white dwarfs) is higher than among hot white dwarfs. In this picture a super-Jupiter residing in the outer regions of the white dwarf's planetary system is perturbed into a highly eccentric orbit by a close stellar encounter and is later accreted by the white dwarf.

IC 3475: A stripped dwarf galaxy in the Virgo cluster

International Nuclear Information System (INIS)

Vigroux, L.; Thuan, T.X.; Vader, J.P.; Lachieze-Rey, M.

1986-01-01

We have obtained B and R CCD and H I observations of the Virgo dwarf galaxy IC 3475. The galaxy is remarkable for its very large diameter (approx.10 kpc for a Virgo distance modulus of 31) and is comparable in size to the large dwarfs discussed by Sandage and Binggeli. Its light profile is best fitted by an exponential law, characteristic of a dwarf Magellanic irregular galaxy. It possesses a central bar with many knots and inclusions concentrated toward the center of the galaxy. These knots and inclusions have the same color (B-Rapprox.1.5) as the rest of the galaxy and are best explained as intermediate-age (1--7 x 10 9 yr) star clusters such as those found in the Magellanic Clouds. Despite possessing the photometric structure of a dwarf Magellanic irregular galaxy, IC 3475 contains less than 5.3 x 10 6 M/sub sun/ of neutral hydrogen. Its hydrogen mass to blue light ratio is less than 0.01, approx.60 times less than the mean value observed for dwarf Magellanic irregulars. It is most likely that IC 3475, which is located near the core of the Virgo cluster, is a stripped dwarf galaxy. The very large size of the galaxy (its diameter is approx.1.8 times larger than that of ''normal'' dwarfs) appears to rule out evolution of IC 3475 from a normal dwarf irregular or to a normal dwarf elliptical

Identification of Cherry green ring mottle virus on Sweet Cherry Trees in Korea

Directory of Open Access Journals (Sweden)

In-Sook Cho

2013-12-01

Full Text Available During the 2012 growing season, 154 leaf samples were collected from sweet cherry trees in Hwaseong, Pyeongtaek, Gyeongju, Kimcheon, Daegu, Yeongju and Eumseong and tested for the presence of Cherry green ring mottle virus (CGRMV. PCR products of the expected size (807 bp were obtained from 6 samples. The PCR products were cloned and sequenced. The nucleotide sequences of the clones showed over 88% identities to published coat protein sequences of CGRMV isolates in the GenBank database. The sequences of CGRMV isolates, CGR-KO 1−6 shared 98.8 to 99.8% nucleotide and 99.6 to 100% amino acid similarities. Phylogenetic analysis indicated that the Korean CGRMV isolates belong to the group II of CGRMV coat protein genes. The CGRMV infected sweet cherry trees were also tested for Apple chlorotic leaf spot virus (ACLSV, Apple mosaic virus (ApMV, Cherry necrotic rusty mottle virus (CNRMV, Cherry mottle leaf virus (CMLV, Cherry rasp leaf virus (CRLV, Cherry leafroll virus (CLRV, Cherry virus A (CVA, Little cherry virus 1 (LChV1, Prune dwarf virus (PDV and Prunus necrotic ringspot virus (PNRSV by RT-PCR. All of the tested trees were also infected with ACLSV.

First discovery of acetone extract from cottonseed oil sludge as a novel antiviral agent against plant viruses.

Science.gov (United States)

Zhao, Lei; Feng, Chaohong; Hou, Caiting; Hu, Lingyun; Wang, Qiaochun; Wu, Yunfeng

2015-01-01

A novel acetone extract from cottonseed oil sludge was firstly discovered against plant viruses including Tobacco mosaic virus (TMV), Rice stripe virus (RSV) and Southern rice black streaked dwarf virus (SRBSDV). Gossypol and β-sitosterol separated from the acetone extract were tested for their effects on anti-TMV and analysed by nuclear magnetic resonance (NMR) assay. In vivo and field trials in different geographic distributions and different host varieties declared that this extract mixture was more efficient than the commercial agent Ningnanmycin with a broad spectrum of anti-plant-viruses activity. No phytotoxic activity was observed in the treated plants and environmental toxicology showed that this new acetone extract was environmentally friendly, indicating that this acetone extract has potential application in the control of plant virus in the future.

Kinematically Decoupled Cores in Dwarf (Elliptical) Galaxies

NARCIS (Netherlands)

Toloba, E.; Peletier, R. F.; Guhathakurta, P.; van de Ven, G.; Boissier, S.; Boselli, A.; Brok, M. d.; Falcón-Barroso, J.; Hensler, G.; Janz, J.; Laurikainen, E.; Lisker, T.; Paudel, S.; Ryś, A.; Salo, H.

An overview is given of what we know about the frequency of kinematically decoupled cores in dwarf elliptical galaxies. New observations show that kinematically decoupled cores happen just as often in dwarf elliptical as in ordinary early-type galaxies. This has important consequences for the

K2 Ultracool Dwarfs Survey. II. The White Light Flare Rate of Young Brown Dwarfs

Science.gov (United States)

Gizis, John E.; Paudel, Rishi R.; Mullan, Dermott; Schmidt, Sarah J.; Burgasser, Adam J.; Williams, Peter K. G.

2017-08-01

We use Kepler K2 Campaign 4 short-cadence (one-minute) photometry to measure white light flares in the young, moving group brown dwarfs 2MASS J03350208+2342356 (2M0335+23) and 2MASS J03552337+1133437 (2M0355+11), and report on long-cadence (thirty-minute) photometry of a superflare in the Pleiades M8 brown dwarf CFHT-PL-17. The rotation period (5.24 hr) and projected rotational velocity (45 km s-1) confirm 2M0335+23 is inflated (R≥slant 0.20 {R}⊙ ) as predicted for a 0.06 {M}⊙ , 24 Myr old brown dwarf βPic moving group member. We detect 22 white light flares on 2M0335+23. The flare frequency distribution follows a power-law distribution with slope -α =-1.8+/- 0.2 over the range 1031 to 1033 erg. This slope is similar to that observed in the Sun and warmer flare stars, and is consistent with lower-energy flares in previous work on M6-M8 very-low-mass stars; taking the two data sets together, the flare frequency distribution for ultracool dwarfs is a power law over 4.3 orders of magnitude. The superflare (2.6× {10}34 erg) on CFHT-PL-17 shows higher-energy flares are possible. We detect no flares down to a limit of 2× {10}30 erg in the nearby L5γ AB Dor moving group brown dwarf 2M0355+11, consistent with the view that fast magnetic reconnection is suppressed in cool atmospheres. We discuss two multi-peaked flares observed in 2M0335+23, and argue that these complex flares can be understood as sympathetic flares, in which fast-mode magnetohydrodynamic waves similar to extreme-ultraviolet waves in the Sun trigger magnetic reconnection in different active regions.

Kinematics and stellar populations of 17 dwarf early-type galaxies

OpenAIRE

Thomas, D.; Bender, R.; Hopp, U.; Maraston, C.; Greggio, L.

2002-01-01

We present kinematics and stellar population properties of 17 dwarf early-type galaxies in the luminosity range -14> M_B> -19. Our sample fills the gap between the intensively studied giant elliptical and Local Group dwarf spheroidal galaxies. The dwarf ellipticals of the present sample have constant velocity dispersion profiles within their effective radii and do not show significant rotation, hence are clearly anisotropic. The dwarf lenticulars, instead, rotate faster and are, at least part...

Search for brown dwarfs in the IRAS data bases

International Nuclear Information System (INIS)

Low, F.J.

1986-01-01

A report is given on the initial searches for brown dwarf stars in the IRAS data bases. The paper was presented to the workshop on 'Astrophysics of brown dwarfs', Virginia, USA, 1985. To date no brown dwarfs have been discovered in the solar neighbourhood. Opportunities for future searches with greater sensitivity and different wavelengths are outlined. (U.K.)

Magnetic white dwarfs: Observations, theory and future prospects

Science.gov (United States)

García-Berro, Enrique; Kilic, Mukremin; Kepler, Souza Oliveira

2016-01-01

Isolated magnetic white dwarfs have field strengths ranging from 103G to 109G, and constitute an interesting class of objects. The origin of the magnetic field is still the subject of a hot debate. Whether these fields are fossil, hence the remnants of original weak magnetic fields amplified during the course of the evolution of the progenitor of white dwarfs, or on the contrary, are the result of binary interactions or, finally, other physical mechanisms that could produce such large magnetic fields during the evolution of the white dwarf itself, remains to be elucidated. In this work, we review the current status and paradigms of magnetic fields in white dwarfs, from both the theoretical and observational points of view.

The Andromeda Dwarf Spheroidal Galaxies

OpenAIRE

Armandroff, Taft E.; Da Costa, Gary S.

1998-01-01

Our current knowledge of M31's dwarf spheroidal companions is reviewed. Two topics of recent interest constitute the bulk of this review. First, color-magnitude diagrams reaching below the horizontal branch have been constructed for two M31 dwarf spheroidals based on images from HST/WFPC2. The horizontal branches are predominantly red in both galaxies, redder than expected for their metallicity based on Galactic globular clusters. Thus, the second parameter effect is seen in the M31 halo. Sec...

Carbon-enhanced metal-poor stars in dwarf galaxies

OpenAIRE

Salvadori, Stefania; Skuladottir, Asa; Tolstoy, Eline

2015-01-01

We investigate the frequency and origin of carbon-enhanced metal-poor (CEMP) stars in Local Group dwarf galaxies by means of a statistical, data-calibrated cosmological model for the hierarchical build-up of the Milky Way and its dwarf satellites. The model self-consistently explains the variation with dwarf galaxy luminosity of the observed: i) frequency and [Fe/H] range of CEMP stars; ii) metallicity distribution functions; iii) star formation histories. We show that if primordial faint sup...

The Brown Dwarf Kinematics Project (BDKP. III. Parallaxes for 70 Ultracool Dwarfs

Science.gov (United States)

2012-06-10

a low surface gravity dwarf, Cal is a calibrator ultracool dwarf, SD is an ultracool subdwarf, B is a tight binary unresolved in 2MASS . d F indicates...procedure described in Vrba et al. (2004), we obtained 2MASS photometry for all reference stars. We com- pared with the intrinsic colors described in...140.5 ± 5.8 38.44 ± 2.83 −1191.00 ± 13.00 −115.00 ± 13.00 A 1 2MASS J0746+2000 86.2 ± 4.6 −355.9 ± 5.1 −63.7 ± 5.2 81.90 ± 0.30 −374.04 ± 0.31 −57.91

Ages of M Dwarf Stars from their Alpha Enhancement

Science.gov (United States)

Muirhead, Philip Steven; Veyette, Mark

2018-01-01

M dwarf stars dominate stellar populations, and recent results from NASA's Kepler Mission suggest rocky planets are abundant around M dwarf stars. With so many planets orbiting M dwarfs, exoplanet scientists can now turn to questions about their history and evolution. Unfortunately, measuring fundamental properties of M dwarfs is challenging for a variety of reasons. I will discuss the importance of near-infrared spectroscopy in this effort. With high-resolution near-infrared spectroscopy covering Y to K band, we can measure detailed fundamental properties of low-mass stars. With new techniques to measure stellar alpha and iron abundances, we can begin to measure the most challenging fundamental property of M dwarfs: their age. These efforts are even more exciting in the coming years, when the TESS spacecraft is expected to discover five times as many planets orbiting low-mass stars as Kepler.

A Dark Spot on a Massive White Dwarf

Science.gov (United States)

Kilic, Mukremin; Gianninas, Alexandros; Bell, Keaton J.; Curd, Brandon; Brown, Warren R.; Hermes, J. J.; Dufour, Patrick; Wisniewski, John P.; Winget, D. E.; Winget, K. I.

2015-12-01

We present the serendipitous discovery of eclipse-like events around the massive white dwarf SDSS J152934.98+292801.9 (hereafter J1529+2928). We selected J1529+2928 for time-series photometry based on its spectroscopic temperature and surface gravity, which place it near the ZZ Ceti instability strip. Instead of pulsations, we detect photometric dips from this white dwarf every 38 minutes. Follow-up optical spectroscopy observations with Gemini reveal no significant radial velocity variations, ruling out stellar and brown dwarf companions. A disintegrating planet around this white dwarf cannot explain the observed light curves in different filters. Given the short period, the source of the photometric dips must be a dark spot that comes into view every 38 minutes due to the rotation of the white dwarf. Our optical spectroscopy does not show any evidence of Zeeman splitting of the Balmer lines, limiting the magnetic field strength to B Tecnologia e Inovação (Brazil) and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina).

NUCLEAR CONDENSATE AND HELIUM WHITE DWARFS

Energy Technology Data Exchange (ETDEWEB)

Bedaque, Paulo F.; Berkowitz, Evan [Maryland Center for Fundamental Physics, Department of Physics, University of Maryland, College Park, MD (United States); Cherman, Aleksey, E-mail: bedaque@umd.edu, E-mail: evanb@umd.edu, E-mail: a.cherman@damtp.cam.ac.uk [Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge CB3 0WA (United Kingdom)

2012-04-10

We consider a high-density region of the helium phase diagram, where the nuclei form a Bose-Einstein condensate rather than a classical plasma or a crystal. Helium in this phase may be present in helium-core white dwarfs. We show that in this regime there is a new gapless quasiparticle not previously noticed, arising when the constraints imposed by gauge symmetry are taken into account. The contribution of this quasiparticle to the specific heat of a white dwarf core turns out to be comparable in a range of temperatures to the contribution from the particle-hole excitations of the degenerate electrons. The specific heat in the condensed phase is two orders of magnitude smaller than in the uncondensed plasma phase, which is the ground state at higher temperatures, and four orders of magnitude smaller than the specific heat that an ion lattice would provide, if formed. Since the specific heat of the core is an important input for setting the rate of cooling of a white dwarf star, it may turn out that such a change in the thermal properties of the cores of helium white dwarfs has observable implications.

NUCLEAR CONDENSATE AND HELIUM WHITE DWARFS

International Nuclear Information System (INIS)

Bedaque, Paulo F.; Berkowitz, Evan; Cherman, Aleksey

2012-01-01

We consider a high-density region of the helium phase diagram, where the nuclei form a Bose-Einstein condensate rather than a classical plasma or a crystal. Helium in this phase may be present in helium-core white dwarfs. We show that in this regime there is a new gapless quasiparticle not previously noticed, arising when the constraints imposed by gauge symmetry are taken into account. The contribution of this quasiparticle to the specific heat of a white dwarf core turns out to be comparable in a range of temperatures to the contribution from the particle-hole excitations of the degenerate electrons. The specific heat in the condensed phase is two orders of magnitude smaller than in the uncondensed plasma phase, which is the ground state at higher temperatures, and four orders of magnitude smaller than the specific heat that an ion lattice would provide, if formed. Since the specific heat of the core is an important input for setting the rate of cooling of a white dwarf star, it may turn out that such a change in the thermal properties of the cores of helium white dwarfs has observable implications.

EVIDENCE FOR ACCRETION IN A NEARBY, YOUNG BROWN DWARF

International Nuclear Information System (INIS)

Reiners, Ansgar

2009-01-01

We report on the discovery of the young, nearby, brown dwarf 2MASS J0041353-562112. The object has a spectral type of M7.5; it shows Li absorption and signatures of accretion, which implies that it still has a disk and suggests an age below 10 Myr. The space motion vector and position on the sky indicate that the brown dwarf is probably a member of the ∼20 Myr old Tuc-Hor association, or that it may be an ejected member of the ∼12 Myr old β Pic association; both would imply that 2MASS J0041353-562112 may in fact be older than 10 Myr. No accreting star or brown dwarf was previously known in these associations. Assuming an age of 10 Myr, the brown dwarf has a mass of about 30 M Jup and is located at 35 pc distance. The newly discovered object is the closest accreting brown dwarf known. Its membership to an association older than 10 Myr implies that either disks in brown dwarfs can survive as long as in more massive stars, perhaps even longer, or that star formation in Tuc-Hor or β Pic occurred more recently than previously thought. The history and evolution of this object can provide new fundamental insight into the formation process of stars, brown dwarfs, and planets.

Hepatic response to oxidative injury in long-lived Ames dwarf mice.

Science.gov (United States)

Sun, Liou Y; Bokov, Alex F; Richardson, Arlan; Miller, Richard A

2011-01-01

Multiple stress resistance pathways were evaluated in the liver of Ames dwarf mice before and after exposure to the oxidative toxin diquat, seeking clues to the exceptional longevity conferred by this mutation. Before diquat treatment, Ames dwarf mice, compared with nonmutant littermate controls, had 2- to 6-fold higher levels of expression of mRNAs for immediate early genes and 2- to 5-fold higher levels of mRNAs for genes dependent on the transcription factor Nrf2. Diquat led to a 2-fold increase in phosphorylation of the stress kinase ERK in control (but not Ames dwarf) mice and to a 50% increase in phosphorylation of the kinase JNK2 in Ames dwarf (but not control) mice. Diquat induction of Nrf2 protein was higher in dwarf mice than in controls. Of 6 Nrf2-responsive genes evaluated, 4 (HMOX, NQO-1, MT-1, and MT-2) remained 2- to 10-fold lower in control than in dwarf liver after diquat, and the other 2 (GCLM and TXNRD) reached levels already seen in dwarf liver at baseline. Thus, livers of Ames dwarf mice differ systematically from controls in multiple stress resistance pathways before and after exposure to diquat, suggesting mechanisms for stress resistance and extended longevity in Ames dwarf mice.

Unusual Slowly Rotating Brown Dwarfs Discovered through Precision Spitzer Photometry

Science.gov (United States)

Heinze, Aren; Metchev, S.

2014-01-01

Many brown dwarfs exhibit low-amplitude rotationally modulated variability due to photospheric inhomogeneities caused by condensate clouds in their atmospheres. The Spitzer Space Telescope 'Weather on Other Worlds' (WoW) project has monitored 44 brown dwarfs at unprecedented photometric precision from space. We present one of several important new results from WoW: the discovery of brown dwarfs with unexpectedly slow rotation periods. While most brown dwarfs have periods of 2-12 hours, we have identified two with well-constrained periods of 13±1 and >20 hours, respectively, and 2 others that show more tentative evidence of longer than 20-hour periods. By serving as almost non-rotating standards, these objects will allow more accurate calibration of spectroscopic measurements of brown dwarfs' projected rotational velocities. The existence of such slowly-rotating objects also constrains models of brown dwarf formation and angular momentum evolution.

THE POST-MERGER MAGNETIZED EVOLUTION OF WHITE DWARF BINARIES: THE DOUBLE-DEGENERATE CHANNEL OF SUB-CHANDRASEKHAR TYPE Ia SUPERNOVAE AND THE FORMATION OF MAGNETIZED WHITE DWARFS

International Nuclear Information System (INIS)

Ji Suoqing; Fisher, Robert T.; García-Berro, Enrique; Tzeferacos, Petros; Jordan, George; Lee, Dongwook; Lorén-Aguilar, Pablo; Cremer, Pascal; Behrends, Jan

2013-01-01

Type Ia supernovae (SNe Ia) play a crucial role as standardizable cosmological candles, though the nature of their progenitors is a subject of active investigation. Recent observational and theoretical work has pointed to merging white dwarf binaries, referred to as the double-degenerate channel, as the possible progenitor systems for some SNe Ia. Additionally, recent theoretical work suggests that mergers which fail to detonate may produce magnetized, rapidly rotating white dwarfs. In this paper, we present the first multidimensional simulations of the post-merger evolution of white dwarf binaries to include the effect of the magnetic field. In these systems, the two white dwarfs complete a final merger on a dynamical timescale, and are tidally disrupted, producing a rapidly rotating white dwarf merger surrounded by a hot corona and a thick, differentially rotating disk. The disk is strongly susceptible to the magnetorotational instability (MRI), and we demonstrate that this leads to the rapid growth of an initially dynamically weak magnetic field in the disk, the spin-down of the white dwarf merger, and to the subsequent central ignition of the white dwarf merger. Additionally, these magnetized models exhibit new features not present in prior hydrodynamic studies of white dwarf mergers, including the development of MRI turbulence in the hot disk, magnetized outflows carrying a significant fraction of the disk mass, and the magnetization of the white dwarf merger to field strengths ∼2 × 10 8 G. We discuss the impact of our findings on the origins, circumstellar media, and observed properties of SNe Ia and magnetized white dwarfs

The Post-merger Magnetized Evolution of White Dwarf Binaries: The Double-degenerate Channel of Sub-Chandrasekhar Type Ia Supernovae and the Formation of Magnetized White Dwarfs

Science.gov (United States)

Ji, Suoqing; Fisher, Robert T.; García-Berro, Enrique; Tzeferacos, Petros; Jordan, George; Lee, Dongwook; Lorén-Aguilar, Pablo; Cremer, Pascal; Behrends, Jan

2013-08-01

Type Ia supernovae (SNe Ia) play a crucial role as standardizable cosmological candles, though the nature of their progenitors is a subject of active investigation. Recent observational and theoretical work has pointed to merging white dwarf binaries, referred to as the double-degenerate channel, as the possible progenitor systems for some SNe Ia. Additionally, recent theoretical work suggests that mergers which fail to detonate may produce magnetized, rapidly rotating white dwarfs. In this paper, we present the first multidimensional simulations of the post-merger evolution of white dwarf binaries to include the effect of the magnetic field. In these systems, the two white dwarfs complete a final merger on a dynamical timescale, and are tidally disrupted, producing a rapidly rotating white dwarf merger surrounded by a hot corona and a thick, differentially rotating disk. The disk is strongly susceptible to the magnetorotational instability (MRI), and we demonstrate that this leads to the rapid growth of an initially dynamically weak magnetic field in the disk, the spin-down of the white dwarf merger, and to the subsequent central ignition of the white dwarf merger. Additionally, these magnetized models exhibit new features not present in prior hydrodynamic studies of white dwarf mergers, including the development of MRI turbulence in the hot disk, magnetized outflows carrying a significant fraction of the disk mass, and the magnetization of the white dwarf merger to field strengths ~2 × 108 G. We discuss the impact of our findings on the origins, circumstellar media, and observed properties of SNe Ia and magnetized white dwarfs.

THE POST-MERGER MAGNETIZED EVOLUTION OF WHITE DWARF BINARIES: THE DOUBLE-DEGENERATE CHANNEL OF SUB-CHANDRASEKHAR TYPE Ia SUPERNOVAE AND THE FORMATION OF MAGNETIZED WHITE DWARFS

Energy Technology Data Exchange (ETDEWEB)

Ji Suoqing; Fisher, Robert T. [University of Massachusetts Dartmouth, Department of Physics, 285 Old Westport Road, North Dartmouth, MA 02740 (United States); Garcia-Berro, Enrique [Departament de Fisica Aplicada, Universitat Politecnica de Catalunya, c/Esteve Terrades, 5, E-08860 Castelldefels (Spain); Tzeferacos, Petros; Jordan, George; Lee, Dongwook [Center for Astrophysical Thermonuclear Flashes, The University of Chicago, Chicago, IL 60637 (United States); Loren-Aguilar, Pablo [School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom); Cremer, Pascal [Bethe Center for Theoretical Physics, Universitaet Bonn, Nussallee 12, D-53115 Bonn (Germany); Behrends, Jan [Fachbereich Physik, Freie Universitaet Berlin, Arnimallee 14, D-14195 Berlin (Germany)

2013-08-20

Type Ia supernovae (SNe Ia) play a crucial role as standardizable cosmological candles, though the nature of their progenitors is a subject of active investigation. Recent observational and theoretical work has pointed to merging white dwarf binaries, referred to as the double-degenerate channel, as the possible progenitor systems for some SNe Ia. Additionally, recent theoretical work suggests that mergers which fail to detonate may produce magnetized, rapidly rotating white dwarfs. In this paper, we present the first multidimensional simulations of the post-merger evolution of white dwarf binaries to include the effect of the magnetic field. In these systems, the two white dwarfs complete a final merger on a dynamical timescale, and are tidally disrupted, producing a rapidly rotating white dwarf merger surrounded by a hot corona and a thick, differentially rotating disk. The disk is strongly susceptible to the magnetorotational instability (MRI), and we demonstrate that this leads to the rapid growth of an initially dynamically weak magnetic field in the disk, the spin-down of the white dwarf merger, and to the subsequent central ignition of the white dwarf merger. Additionally, these magnetized models exhibit new features not present in prior hydrodynamic studies of white dwarf mergers, including the development of MRI turbulence in the hot disk, magnetized outflows carrying a significant fraction of the disk mass, and the magnetization of the white dwarf merger to field strengths {approx}2 Multiplication-Sign 10{sup 8} G. We discuss the impact of our findings on the origins, circumstellar media, and observed properties of SNe Ia and magnetized white dwarfs.

Productivity of lactating cows fed on a diet of haylage from a vetch pea-oat mixture with the introduction of new biological preservative

Directory of Open Access Journals (Sweden)

P. I. Baryshnikov

2016-10-01

Full Text Available The effect of a new biological preservative representing a mix of lyophilized Lactobacillus plantarum VKPM V-4173, Lactococcus lactis subsp. lactis VKPM V-2092 and Propionibacterium acidipropionici VKPMV-5723 strains (40 : 40 : 20 on the quality of haylage prepared from a mix of vetch, oats, and pea has been studied. The total bacteria content in the preservative was 1·1011 CFU/g. Five different variants of conservation of alfalfa haylage prepared at the budding stage were evaluated under laboratory conditions. The variants included a self-conserved control and the preservative at two different dosages (3 and 6 g/ton with and without the addition of cellulolytic enzymes. The best results were observed in the case of both the enzyme-free and the enzyme-containing preservative at the dosage equal to 6 g/ton. These variants provided the maximum protein content in the haylage (94.3% and 94.5% of the initial content, respectively and a high content of lactic acid (62.9% and 65.4% of the total acid content, respectively and also good organoleptic characteristics. The determined optimum biopreservative dosage was tested under industrial conditions using 750 tons of vetch-oats-pea haylage. The use of the biopreservative provided a high-quality haylage of high nutritive value. Industrial evaluation of the effect on the productivity of milk cattle (n = 15 of the addition of the biopreservative to the haylage showed that the maximum average daily yield of milk with basic fat content (3.4% was obtained from cows of the experimental group whose ration included haylage prepared with the use of the studied preservative. This yield came to32.7 kg , which exceeded the yield for the control group (fed on self-conserved haylage by 7.0%. Three months feeding of cows with the haylage prepared with the use of the new preservative brought a significant saving of money (4,862 rubles per a head at the prices of 2015–2016.

Evidence for dwarf stars at D of about 100 kiloparsecs near the Sextans dwarf spheroidal galaxy

Science.gov (United States)

Gould, Andrew; Guhathakurta, Puragra; Richstone, Douglas; Flynn, Chris

1992-01-01

A method is presented for detecting individual, metal-poor, dwarf stars at distances less than about 150 kpc - a method specifically designed to filter out stars from among the much more numerous faint background field galaxies on the basis of broad-band colors. This technique is applied to two fields at high Galactic latitude, for which there are deep CCD data in four bands ranging from 3600 to 9000 A. The field in Sextans probably contains more than about five dwarf stars with BJ not greater than 25.5. These are consistent with being at a common distance about 100 kpc and lie about 1.7 deg from the newly discovered dwarf galaxy in Sextans whose distance is about 85 +/- 10 kpc. The stars lie near the major axis of the galaxy and are near or beyond the tidal radius. The second field, toward the south Galactic pole, may contain up to about five extra-Galactic stars, but these show no evidence for being at a common distance. Possible applications of this type technique are discussed, and it is shown that even very low surface brightness star clusters or dwarf galaxies may be detected at distances less than about 1 Mpc.

The mass and radius of the M dwarf companion to GD 448

OpenAIRE

Maxted, P. F. L.; Marsh, T. R.; Moran, C.; Dhillon, V. S.; Hilditch, R. W.

1998-01-01

We present spectroscopy and photometry of GD 448, a detached white dwarf - M dwarf binary with a period of 2.47h. We find that the NaI 8200A feature is composed of narrow emission lines due to irradiation of the M dwarf by the white dwarf within broad absorption lines that are essentially unaffected by heating. Combined with an improved spectroscopic orbit and gravitational red shift measurement from spectra of the H-alpha line, we are able to derive masses for the white dwarf and M dwarf dir...

Periodic optical variability of radio-detected ultracool dwarfs

International Nuclear Information System (INIS)

Harding, L. K.; Golden, A.; Singh, Navtej; Sheehan, B.; Butler, R. F.; Hallinan, G.; Boyle, R. P.; Zavala, R. T.

2013-01-01

A fraction of very low mass stars and brown dwarfs are known to be radio active, in some cases producing periodic pulses. Extensive studies of two such objects have also revealed optical periodic variability, and the nature of this variability remains unclear. Here, we report on multi-epoch optical photometric monitoring of six radio-detected dwarfs, spanning the ∼M8-L3.5 spectral range, conducted to investigate the ubiquity of periodic optical variability in radio-detected ultracool dwarfs. This survey is the most sensitive ground-based study carried out to date in search of periodic optical variability from late-type dwarfs, where we obtained 250 hr of monitoring, delivering photometric precision as low as ∼0.15%. Five of the six targets exhibit clear periodicity, in all cases likely associated with the rotation period of the dwarf, with a marginal detection found for the sixth. Our data points to a likely association between radio and optical periodic variability in late-M/early-L dwarfs, although the underlying physical cause of this correlation remains unclear. In one case, we have multiple epochs of monitoring of the archetype of pulsing radio dwarfs, the M9 TVLM 513–46546, spanning a period of 5 yr, which is sufficiently stable in phase to allow us to establish a period of 1.95958 ± 0.00005 hr. This phase stability may be associated with a large-scale stable magnetic field, further strengthening the correlation between radio activity and periodic optical variability. Finally, we find a tentative spin-orbit alignment of one component of the very low mass binary, LP 349–25.

Periodic optical variability of radio-detected ultracool dwarfs

Energy Technology Data Exchange (ETDEWEB)

Harding, L. K.; Golden, A.; Singh, Navtej; Sheehan, B.; Butler, R. F. [Centre for Astronomy, National University of Ireland, Galway, University Road, Galway (Ireland); Hallinan, G. [Cahill Center for Astrophysics, California Institute of Technology, 1200 East California Boulevard, MC 249-17, Pasadena, CA 91125 (United States); Boyle, R. P. [Vatican Observatory Research Group, Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States); Zavala, R. T., E-mail: lkh@astro.caltech.edu [United States Naval Observatory, Flagstaff Station, Flagstaff, AZ 86001 (United States)

2013-12-20

A fraction of very low mass stars and brown dwarfs are known to be radio active, in some cases producing periodic pulses. Extensive studies of two such objects have also revealed optical periodic variability, and the nature of this variability remains unclear. Here, we report on multi-epoch optical photometric monitoring of six radio-detected dwarfs, spanning the ∼M8-L3.5 spectral range, conducted to investigate the ubiquity of periodic optical variability in radio-detected ultracool dwarfs. This survey is the most sensitive ground-based study carried out to date in search of periodic optical variability from late-type dwarfs, where we obtained 250 hr of monitoring, delivering photometric precision as low as ∼0.15%. Five of the six targets exhibit clear periodicity, in all cases likely associated with the rotation period of the dwarf, with a marginal detection found for the sixth. Our data points to a likely association between radio and optical periodic variability in late-M/early-L dwarfs, although the underlying physical cause of this correlation remains unclear. In one case, we have multiple epochs of monitoring of the archetype of pulsing radio dwarfs, the M9 TVLM 513–46546, spanning a period of 5 yr, which is sufficiently stable in phase to allow us to establish a period of 1.95958 ± 0.00005 hr. This phase stability may be associated with a large-scale stable magnetic field, further strengthening the correlation between radio activity and periodic optical variability. Finally, we find a tentative spin-orbit alignment of one component of the very low mass binary, LP 349–25.

SURPRISINGLY WEAK MAGNETISM ON YOUNG ACCRETING BROWN DWARFS

International Nuclear Information System (INIS)

Reiners, A.; Basri, G.; Christensen, U. R.

2009-01-01

We have measured the surface magnetic flux on four accreting young brown dwarfs and one nonaccreting young very low mass (VLM) star utilizing high-resolution spectra of absorption lines of the FeH molecule. A magnetic field of 1-2 kG had been proposed for one of the brown dwarfs, Two Micron All Sky Survey (2MASS) J1207334-393254, because of its similarities to higher mass T Tauri stars as manifested in accretion and the presence of a jet. We do not find clear evidence for a kilogauss field in any of our young brown dwarfs but do find a 2 kG field on the young VLM star. Our 3σ upper limit for the magnetic flux in 2MASS J1207334-393254 just reaches 1 kG. We estimate the magnetic field required for accretion in young brown dwarfs given the observed rotations, and find that fields of only a few hundred gauss are sufficient for magnetospheric accretion. This predicted value is less than our observed upper limit. We conclude that magnetic fields in young brown dwarfs are a factor of 5 or more lower than in young stars of about one solar mass, and in older stars with spectral types similar to our young brown dwarfs. It is interesting that, during the first few million years, the fields scale down with mass in line with what is needed for magnetospheric accretion, yet no such scaling is observed at later ages within the same effective temperature range. This scaling is opposite to the trend in rotation, with shorter rotation periods for very young accreting brown dwarfs compared with accreting solar-mass objects (and very low Rossby numbers in all cases). We speculate that in young objects a deeper intrinsic connection may exist between magnetospheric accretion and magnetic field strength, or that magnetic field generation in brown dwarfs may be less efficient than in stars. Neither of these currently has an easy physical explanation.

Searching for white dwarfs candidates in Sloan Digital Sky Survey Data

International Nuclear Information System (INIS)

Nalezyty, Miroslaw; Majczyna, Agnieszka; Ciechanowska, Anna; Madej, Jerzy

2009-01-01

Large amount of observational spectroscopic data are recently available from different observational projects, like Sloan Digital Sky Survey. It's become more urgent to identify white dwarfs stars based on data itself i.e. without modelling white dwarf atmospheres. In particular, existing methods of white dwarfs identification presented in Kleinman et al. (2004) and in Eisenstein et al. (2006) did not allow to find all the white dwarfs in examined data. We intend to test various criteria of searching for white dwarf candidates, based on photometric and spectral features.

A Panchromatic View of Brown Dwarf Aurorae

Energy Technology Data Exchange (ETDEWEB)

Pineda, J. Sebastian [University of Colorado Boulder, Laboratory for Atmospheric and Space Physics, 3665 Discovery Drive, Boulder CO, 80303 (United States); Hallinan, Gregg; Kao, Melodie M. [California Institute of Technology, Department of Astronomy, 1200 E. California Avenue, Pasadena CA, 91125 (United States)

2017-09-01

Stellar coronal activity has been shown to persist into the low-mass star regime, down to late M-dwarf spectral types. However, there is now an accumulation of evidence suggesting that at the end of the main sequence, there is a transition in the nature of the magnetic activity from chromospheric and coronal to planet-like and auroral, from local impulsive heating via flares and MHD wave dissipation to energy dissipation from strong large-scale magnetospheric current systems. We examine this transition and the prevalence of auroral activity in brown dwarfs through a compilation of multiwavelength surveys of magnetic activity, including radio, X-ray, and optical. We compile the results of those surveys and place their conclusions in the context of auroral emission as a consequence of large-scale magnetospheric current systems that accelerate energetic electron beams and drive the particles to impact the cool atmospheric gas. We explore the different manifestations of auroral phenomena, like H α , in brown dwarf atmospheres and define their distinguishing characteristics. We conclude that large-amplitude photometric variability in the near-infrared is most likely a consequence of clouds in brown dwarf atmospheres, but that auroral activity may be responsible for long-lived stable surface features. We report a connection between auroral H α emission and quiescent radio emission in electron cyclotron maser instability pulsing brown dwarfs, suggesting a potential underlying physical connection between quiescent and auroral emissions. We also discuss the electrodynamic engines powering brown dwarf aurorae and the possible role of satellites around these systems both to power the aurorae and seed the magnetosphere with plasma.

Green manuring effect of pure and mixed barley - hairy vetch winter cover crops on maize and processing tomato N nutrition

DEFF Research Database (Denmark)

Tosti, Giacomo; Benincasa, Paolo; Farneselli, Michela

2012-01-01

this can influence the N uptake and N status of different subsequent summer cash crops. In this study the N effect of barley (Hordeum vulgare L.) and hairy vetch (Vicia villosa Roth.) grown in pure stands or in mixtures with different sowing proportion was tested on maize (Zea Mays L.) and processing......Adopting mixtures between legumes and non legumes can be an efficient tool to merge the advantages of the single species in the fall-sown cover crop practice. Nevertheless there is a lack of information on how the species proportion may affect N accumulation and C/N of the cover crops and how...... of the relationship between cover crop C/N and Neff was confirmed, so mixtures can be used to adjust the extent and timing of mineralisation of the incorporated biomass to the subsequent cash crop requirements. Prediction of the cash crops N status on the cover crop C/N appears to be a useful approach, but, it may...

OPTICAL–NEAR-INFRARED PHOTOMETRIC CALIBRATION OF M DWARF METALLICITY AND ITS APPLICATION

International Nuclear Information System (INIS)

Hejazi, N.; Robertis, M. M. De; Dawson, P. C.

2015-01-01

Based on a carefully constructed sample of dwarf stars, a new optical–near-infrared photometric calibration to estimate the metallicity of late-type K and early-to-mid-type M dwarfs is presented. The calibration sample has two parts; the first part includes 18 M dwarfs with metallicities determined by high-resolution spectroscopy and the second part contains 49 dwarfs with metallicities obtained through moderate-resolution spectra. By applying this calibration to a large sample of around 1.3 million M dwarfs from the Sloan Digital Sky Survey and 2MASS, the metallicity distribution of this sample is determined and compared with those of previous studies. Using photometric parallaxes, the Galactic heights of M dwarfs in the large sample are also estimated. Our results show that stars farther from the Galactic plane, on average, have lower metallicity, which can be attributed to the age–metallicity relation. A scarcity of metal-poor dwarf stars in the metallicity distribution relative to the Simple Closed Box Model indicates the existence of the “M dwarf problem,” similar to the previously known G and K dwarf problems. Several more complicated Galactic chemical evolution models which have been proposed to resolve the G and K dwarf problems are tested and it is shown that these models could, to some extent, mitigate the M dwarf problem as well

OPTICAL–NEAR-INFRARED PHOTOMETRIC CALIBRATION OF M DWARF METALLICITY AND ITS APPLICATION

Energy Technology Data Exchange (ETDEWEB)

Hejazi, N.; Robertis, M. M. De [Physics and Astronomy Department, York University, Toronto, ON M3J 1P3 (Canada); Dawson, P. C., E-mail: nedahej@yorku.ca, E-mail: mmdr@yorku.ca, E-mail: pdawson@trentu.ca [Physics Department, Trent University, Peterborough, K9J 7B8 (Canada)

2015-04-15

Based on a carefully constructed sample of dwarf stars, a new optical–near-infrared photometric calibration to estimate the metallicity of late-type K and early-to-mid-type M dwarfs is presented. The calibration sample has two parts; the first part includes 18 M dwarfs with metallicities determined by high-resolution spectroscopy and the second part contains 49 dwarfs with metallicities obtained through moderate-resolution spectra. By applying this calibration to a large sample of around 1.3 million M dwarfs from the Sloan Digital Sky Survey and 2MASS, the metallicity distribution of this sample is determined and compared with those of previous studies. Using photometric parallaxes, the Galactic heights of M dwarfs in the large sample are also estimated. Our results show that stars farther from the Galactic plane, on average, have lower metallicity, which can be attributed to the age–metallicity relation. A scarcity of metal-poor dwarf stars in the metallicity distribution relative to the Simple Closed Box Model indicates the existence of the “M dwarf problem,” similar to the previously known G and K dwarf problems. Several more complicated Galactic chemical evolution models which have been proposed to resolve the G and K dwarf problems are tested and it is shown that these models could, to some extent, mitigate the M dwarf problem as well.

A SEARCH FOR ASTEROIDS, MOONS, AND RINGS ORBITING WHITE DWARFS

International Nuclear Information System (INIS)

Di Stefano, Rosanne; Howell, Steve B.; Kawaler, Steven D.

2010-01-01

Do white dwarfs host asteroid systems? Although several lines of argument suggest that white dwarfs may be orbited by large populations of asteroids, transits would provide the most direct evidence. We demonstrate that the Kepler mission has the capability to detect transits of white dwarfs by asteroids. Because white-dwarf asteroid systems, if they exist, are likely to contain many asteroids orbiting in a spatially extended distribution, discoveries of asteroid transits can be made by monitoring only a small number of white dwarfs, compatible with Kepler's primary mission, which is to monitor stars with potentially habitable planets. Possible future missions that survey 10 times as many stars with similar sensitivity and minute-cadence monitoring can establish the characteristics of asteroid systems around white dwarfs, such as the distribution of asteroid sizes and semimajor axes. Transits by planets would be more dramatic, but the probability that they will occur is lower. Ensembles of planetary moons and/or the presence of rings around planets can also produce transits detectable by Kepler. The presence of moons and rings can significantly increase the probability that Kepler will discover planets orbiting white dwarfs, even while monitoring only a small number of them.

KECK NIRSPEC RADIAL VELOCITY OBSERVATIONS OF LATE-M DWARFS

Energy Technology Data Exchange (ETDEWEB)

Tanner, Angelle; White, Russel [Department of Astronomy, Georgia State University, One Park Place, Atlanta, GA 30303 (United States); Bailey, John [Department of Astronomy, University of Michigan, 830 Dennison Building, 500 Church Street, Ann Arbor, MI 48109-1042 (United States); Blake, Cullen [Department of Astrophysical Sciences, Princeton University, Peyton Hall, Ivy Lane, Princeton, NJ 08544 (United States); Blake, Geoffrey [Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 (United States); Cruz, Kelle [Department of Physics and Astronomy, Hunter College, 695 Park Avenue, New York, NY 10065 (United States); Burgasser, Adam J. [Center for Astrophysics and Space Science, University of California San Diego, La Jolla, CA 92093 (United States); Kraus, Adam [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States)

2012-11-15

We present the results of an infrared spectroscopic survey of 23 late-M dwarfs with the NIRSPEC echelle spectrometer on the Keck II telescope. Using telluric lines for wavelength calibration, we are able to achieve measurement precisions of down to 45 m s{sup -1} for our late-M dwarfs over a one- to four-year long baseline. Our sample contains two stars with radial velocity (RV) variations of >1000 m s{sup -1}. While we require more measurements to determine whether these RV variations are due to unseen planetary or stellar companions or are the result of starspots known to plague the surface of M dwarfs, we can place upper limits of <40 M{sub J} sin i on the masses of any companions around those two M dwarfs with RV variations of <160 m s{sup -1} at orbital periods of 10-100 days. We have also measured the rotational velocities for all the stars in our late-M dwarf sample and offer our multi-order, high-resolution spectra over 2.0-2.4 {mu}m to the atmospheric modeling community to better understand the atmospheres of late-M dwarfs.

KECK NIRSPEC RADIAL VELOCITY OBSERVATIONS OF LATE-M DWARFS

International Nuclear Information System (INIS)

Tanner, Angelle; White, Russel; Bailey, John; Blake, Cullen; Blake, Geoffrey; Cruz, Kelle; Burgasser, Adam J.; Kraus, Adam

2012-01-01

We present the results of an infrared spectroscopic survey of 23 late-M dwarfs with the NIRSPEC echelle spectrometer on the Keck II telescope. Using telluric lines for wavelength calibration, we are able to achieve measurement precisions of down to 45 m s –1 for our late-M dwarfs over a one- to four-year long baseline. Our sample contains two stars with radial velocity (RV) variations of >1000 m s –1 . While we require more measurements to determine whether these RV variations are due to unseen planetary or stellar companions or are the result of starspots known to plague the surface of M dwarfs, we can place upper limits of J sin i on the masses of any companions around those two M dwarfs with RV variations of –1 at orbital periods of 10-100 days. We have also measured the rotational velocities for all the stars in our late-M dwarf sample and offer our multi-order, high-resolution spectra over 2.0-2.4 μm to the atmospheric modeling community to better understand the atmospheres of late-M dwarfs.

Mass-Accretion effects on white dwarf interiors

International Nuclear Information System (INIS)

Canal, R.; Hernanz, M.; Isern, J.; Labay, J.; Mochkovitch, R.

1986-01-01

There is observational evidence of the presence of young neutron stars in old binary systems. A likely explanation is that those neutron stars were produced in the collapse of old C+O white dwarfs. Old white dwarfs being cold and at least partially solid, accretion-induced mass growth should finally lead in a number of cases, to their collapse rather than to their explosion. We show in detail how mass accretion on initially solid white dwarfs can leave central solid cores when dynamical instability sets in. We also study the different effects of the existence of such cores on the outcome of the competition between thermonuclear explosion and gravitational collapse

Dwarf spheroidal galaxies: Keystones of galaxy evolution

Science.gov (United States)

Gallagher, John S., III; Wyse, Rosemary F. G.

1994-01-01

Dwarf spheroidal galaxies are the most insignificant extragalactic stellar systems in terms of their visibility, but potentially very significant in terms of their role in the formation and evolution of much more luminous galaxies. We discuss the present observational data and their implications for theories of the formation and evolution of both dwarf and giant galaxies. The putative dark-matter content of these low-surface-brightness systems is of particular interest, as is their chemical evolution. Surveys for new dwarf spheroidals hidden behind the stars of our Galaxy and those which are not bound to giant galaxies may give new clues as to the origins of this unique class of galaxy.

Localized thermonuclear runaways and volcanoes on degenerate dwarf stars

Energy Technology Data Exchange (ETDEWEB)

Shara, M.M.

1982-10-15

Practically all studies to date of thermonuclear runaways on degenerate dwarf stars in binary systems have considered only spherically symmetric eruptions. We emphasize that even slightly non-spherically symmetric accretion leads to transverse temperature gradients in the dwarfs' accreted envelopes. Over a rather broad range of parameter space, thermalization time scales in accreted envelopes are much longer than thermonuclear runaway time scales. Thus localized thermonuclear runaways (i.e., runaways much smaller than the host degenerate star) rather than spherically symmetric global eruptions are likely to occur on many degenerate dwarfs. Localized runaways are more likely to occur on more massive and/or hotter dwarfs.

Origin of the DA and non-DA white dwarf stars

Science.gov (United States)

Shipman, Harry L.

1989-01-01

Various proposals for the bifurcation of the white dwarf cooling sequence are reviewed. 'Primordial' theories, in which the basic bifurcation of the white dwarf sequence is rooted in events predating the white dwarf stage of stellar evolution, are discussed, along with the competing 'mixing' theories in which processes occurring during the white dwarf stage are responsible for the existence of DA or non-DA stars. A new proposal is suggested, representing a two-channel scenario. In the DA channel, some process reduces the hydrogen layer mass to the value of less than 10 to the -7th. The non-DA channel is similar to that in the primordial scenario. These considerations suggest that some mechanism operates in both channels to reduce the thickness of the outermost layer of the white dwarf. It is also noted that accretion from the interstellar medium has little to do with whether a particular white dwarf becomes a DA or a non-DA star.

External morphology of the cycliophoran dwarf male

DEFF Research Database (Denmark)

Neves, Ricardo Cardoso; da Cunha, Maria Ribeiro; Funch, Peter

2010-01-01

the phylum was first described, the dwarf male has a remarkably complex bodyplan albeit its very small size (approx. 30–40 lm in length). Aiming to increase the knowledge on the gross morphology of the cycliophoran dwarf male, specimens from S. pandora and S. americanus were analyzed by scanning electron...

Stars at Low Metallicity in Dwarf Galaxies

NARCIS (Netherlands)

Tolstoy, Eline; Battaglia, Giuseppina; Cole, Andrew; Hunt, LK; Madden, S; Schneider, R

2008-01-01

Dwarf galaxies offer an opportunity to understand the properties of low metallicity star formation both today and at the earliest times at the, epoch of the formation of the first stars. Here we concentrate on two galaxies in the Local Group: the dwarf irregular galaxy Leo A, which has been the

Metals and ionizing photons from dwarf galaxies

NARCIS (Netherlands)

Salvadori, S.; Tolstoy, E.; Ferrara, A.; Zaroubi, S.

We estimate the potential contribution of M <10(9)M(circle dot) dwarf galaxies to the reionization and early metal enrichment of the Milky Way environment, or circum-Galactic medium. Our approach is to use the observed properties of ancient stars ()under tilde>12 Gyr old) measured in nearby dwarf

Convective mixing and accretion in white dwarfs

International Nuclear Information System (INIS)

Koester, D.

1976-01-01

The evolution of convection zones in cooling white dwarfs with helium envelopes and outer hydrogen layers is calculated with a complete stellar evolution code. It is shown that white dwarfs of spectral type DB cannot be formed from DA stars by convective mixing. However, for cooler temperatures (Tsub(e) [de

White dwarf planets

Directory of Open Access Journals (Sweden)

Bonsor Amy

2013-04-01

Full Text Available The recognition that planets may survive the late stages of stellar evolution, and the prospects for finding them around White Dwarfs, are growing. We discuss two aspects governing planetary survival through stellar evolution to the White Dwarf stage. First we discuss the case of a single planet, and its survival under the effects of stellar mass loss, radius expansion, and tidal orbital decay as the star evolves along the Asymptotic Giant Branch. We show that, for stars initially of 1 − 5 M⊙, any planets within about 1 − 5 AU will be engulfed, this distance depending on the stellar and planet masses and the planet's eccentricity. Planets engulfed by the star's envelope are unlikely to survive. Hence, planets surviving the Asymptotic Giant Branch phase will probably be found beyond ∼ 2 AU for a 1  M⊙ progenitor and ∼ 10 AU for a 5 M⊙ progenitor. We then discuss the evolution of two-planet systems around evolving stars. As stars lose mass, planet–planet interactions become stronger, and many systems stable on the Main Sequence become destabilised following evolution of the primary. The outcome of such instabilities is typically the ejection of one planet, with the survivor being left on an eccentric orbit. These eccentric planets could in turn be responsible for feeding planetesimals into the neighbourhood of White Dwarfs, causing observed pollution and circumstellar discs.

White dwarfs, the galaxy and Dirac's cosmology

International Nuclear Information System (INIS)

Stothers, R.

1976-01-01

Reference is made to the apparent absence, or deficiency, of white dwarfs fainter than about 10 -4 L solar mass. An explanation is here proposed on the basis of Dirac's cosmological hypothesis that the gravitational constant, G, has varied with the time elapsed since the beginning of the expansion of the Universe as t -1 and the number of particles in the Universe has increases as t 2 , if the measurements are made in atomic units. For a white dwarf the Chandrasekhar mass limit is a collection of fundamental constants proportional to Gsup(-3/2) and therefore increases with time as tsup(3/2). In the 'additive' version of Dirac's theory the actual mass, M, of a relatively small object like a star remains essentially unchanged by the creation of new matter in the Universe and hence a white dwarf will become more stable with the course of time; but in the 'multiplicative' version of the theory, M increases as t 2 and may eventually exceed the Chandrasekhar limit, and if this happens, gravitational collapse of the white dwarf into an invisible black hole or neutron star will quickly occur. It is considered interesting to find whether the 'multiplicative' theory may have a bearing on the apparent deficiency of faint white dwarfs, and to consider whether there are any possible consequences for galactic evolution. This is here discussed. (U.K.)

Deriving the true mass of an unresolved Brown Dwarf companion to an M-Dwarf with AO aided astrometry*

Directory of Open Access Journals (Sweden)

Kürster M.

2011-07-01

Full Text Available From radial velocity (RV detections alone one does not get all orbital parameters needed to derive the true mass of a non-transiting, unresolved substellar companion to a star. Additional astrometric measurements are needed to calculate the inclination and the longitude of the ascending node. Until today only few true substellar companion masses have been determined by this method with the HST fine guidance sensor [1, 2]. We aim to derive the true mass of a brown dwarf candidate companion to an early M 2.5V dwarf with groundbased high-resolution astrometry aided by adaptive optics. We found this unique brown dwarf desert object, whose distance to the host star is only 0.42 AU, in our UVES precision RV survey of M dwarfs, inferring a minimum companion mass of 27 Jupiter masses [3]. Combining the data with HIPPARCOS astrometry, we found a probability of only 2.9% that the companion is stellar. We therefore observed the host star together with a reference star within a monitoring program with VLT/NACO to derive the true mass of the companion and establish its nature (brown dwarf vs. star. Simultaneous observations of a reference field in a globular cluster are performed to determine the stability of the adaptive optics (AO plus detector system and check its suitability for such high-precision astrometric measurements over several epochs which are needed to find and analyse extrasolar planet systems.

K-band spectroscopic metallicities and temperatures of M-dwarf stars

Directory of Open Access Journals (Sweden)

Rojas-Ayala Bárbara

2013-04-01

Full Text Available I present the metallicity and effective temperature techniques developed for M dwarf stars by Rojas-Ayala et al. (2010, 2012. These techniques are based on absorption features present in the modest resolution K-band spectra (R∼2700 of M dwarfs and have been calibrated using FGK+M dwarf pairs and synthetic atmosphere models. The H2O-K2 index seems to overestimate the effective temperatures of M dwarfs when compared to interferometric measurements. The metallicity distribution of the M dwarf host candidates by the Kepler Mission hints that jovian-size planets form preferentially around solar and super-solar metallicity environments, while small rocky planet host exhibit a wide range of metallicities, just like in their solar-type counterparts.

Gravitational wave radiation from a double white dwarf system inside our galaxy: a potential method for seeking strange dwarfs

Institute of Scientific and Technical Information of China (English)

Zhan-Kui Lü; Shi-Wei Wu; Zhi-Cheng Zeng

2009-01-01

Like the investigation of double white dwarf (DWD) systems, strange dwarf (SD) - white dwarf (WD) system evolution in Laser Interferometer Space Antenna (LISA)'s absolute amplitude-frequency diagram is investigated. Since there is a strange quark core inside an SD, SDs' radii are significantly smaller than the value predicted by the standard WD model, which may strongly affect the gravitational wave (GW) signal in the mass-transferring phases of binary systems. We study how an SD-WD binary evolves across LISA's absolute amplitude-frequency diagram. In principle, we provide an executable way to detect SDs in the Galaxy's DWD systems by radically new windows offered by GW detectors.

The habitability of planets orbiting M-dwarf stars

Science.gov (United States)

Shields, Aomawa L.; Ballard, Sarah; Johnson, John Asher

2016-12-01

The prospects for the habitability of M-dwarf planets have long been debated, due to key differences between the unique stellar and planetary environments around these low-mass stars, as compared to hotter, more luminous Sun-like stars. Over the past decade, significant progress has been made by both space- and ground-based observatories to measure the likelihood of small planets to orbit in the habitable zones of M-dwarf stars. We now know that most M dwarfs are hosts to closely-packed planetary systems characterized by a paucity of Jupiter-mass planets and the presence of multiple rocky planets, with roughly a third of these rocky M-dwarf planets orbiting within the habitable zone, where they have the potential to support liquid water on their surfaces. Theoretical studies have also quantified the effect on climate and habitability of the interaction between the spectral energy distribution of M-dwarf stars and the atmospheres and surfaces of their planets. These and other recent results fill in knowledge gaps that existed at the time of the previous overview papers published nearly a decade ago by Tarter et al. (2007) and Scalo et al. (2007). In this review we provide a comprehensive picture of the current knowledge of M-dwarf planet occurrence and habitability based on work done in this area over the past decade, and summarize future directions planned in this quickly evolving field.

White dwarf stars exceeding the Chandrasekhar mass limit

Science.gov (United States)

Tomaschitz, Roman

2018-01-01

The effect of nonlinear ultra-relativistic electron dispersion on the mass-radius relation of high-mass white dwarfs is studied. The dispersion is described by a permeability tensor in the Dirac equation, generated by the ionized high-density stellar matter, which constitutes the neutralizing background of the nearly degenerate electron plasma. The electron dispersion results in a stable mass-radius relation for high-mass white dwarfs, in contrast to a mass limit in the case of vacuum permeabilities. In the ultra-relativistic regime, the dispersion relation is a power law whose amplitude and scaling exponent is inferred from mass and radius estimates of two high-mass white dwarfs, Sirius B and LHS 4033. Evidence for the existence of super-Chandrasekhar mass white dwarfs is provided by several Type Ia supernovae (e.g., SN 2013cv, SN 2003fg, SN 2007if and SN 2009dc), whose mass ejecta exceed the Chandrasekhar limit by up to a factor of two. The dispersive mass-radius relation is used to estimate the radii, central densities, Fermi temperatures, bulk and compression moduli and sound velocities of their white dwarf progenitors.

A DEEPLY ECLIPSING DETACHED DOUBLE HELIUM WHITE DWARF BINARY

International Nuclear Information System (INIS)

Parsons, S. G.; Marsh, T. R.; Gaensicke, B. T.; Drake, A. J.; Koester, D.

2011-01-01

Using Liverpool Telescope+RISE photometry we identify the 2.78 hr period binary star CSS 41177 as a detached eclipsing double white dwarf binary with a 21,100 K primary star and a 10,500 K secondary star. This makes CSS 41177 only the second known eclipsing double white dwarf binary after NLTT 11748. The 2 minute long primary eclipse is 40% deep and the secondary eclipse 10% deep. From Gemini+GMOS spectroscopy, we measure the radial velocities of both components of the binary from the Hα absorption line cores. These measurements, combined with the light curve information, yield white dwarf masses of M 1 = 0.283 ± 0.064 M sun and M 2 = 0.274 ± 0.034 M sun , making them both helium core white dwarfs. As an eclipsing, double-lined spectroscopic binary, CSS 41177 is ideally suited to measuring precise, model-independent masses and radii. The two white dwarfs will merge in roughly 1.1 Gyr to form a single sdB star.

He stars and He-accreting CO white dwarfs

International Nuclear Information System (INIS)

Limongi, M.; Tornambe, A.

1991-01-01

He star models in the mass range 0.4-1.0 solar mass have been evolved until the red giant phase or, depending on their mass, until crystallization on the white-dwarf cooling sequence. Some of the degenerate structures obtained in these computations have been successively accreted at various He accretion rates in order to better define the fate of the accreting dwarf versus its mass and accretion rate for a fixed degeneracy level of the accreting dwarf. He stars have been further induced to transfer mass to a degenerate companion through Roche lobe overflow, in conditions of large gravitational wave radiation by the system. CO dwarfs in binary systems with He stars are found to experience a thermal behavior whose effects are such to locate the structure on the verge of obtaining a strong SN-like explosive event. 22 refs

White Dwarfs in the HET Dark Energy Experiment

Science.gov (United States)

Castanheira, B. G.; Winget, D. E.; Williams, K.; Montgomery, M. H.; Falcon, R. E.; Hermes, J. J.

2010-11-01

In the past decades, large scale surveys have discovered a large number of white dwarfs. For example, the Sloan Digital Sky Survey (SDSS) Data Release 7 [5] lists about 20 000 spectroscopically confirmed new white dwarfs. More than just a number, the new discoveries revealed different flavors of white dwarfs, including a new class of pulsators [7] and a larger percentage of stars with a magnetic field [4]. The HET Dark Energy Experiment (HETDEX) will use the 9.2 m Hobby-Eberly Telescope at McDonald Observatory and a set of 150 spectrographs to map the three-dimensional positions of one million galaxies. The main goal of the survey is to probe dark energy by observing the recent universe (2products. We expect to obtain spectra for about 10 000 white dwarfs in the next 3 to 4 years.

Doubling the number of pulsating DB white dwarfs

International Nuclear Information System (INIS)

Nitta, Atsuko; Kleinman, S J; Krzenski, J; Kepler, S O; Metcalfe, T S; Mukadam, Anjum S; Mullally, F; Nather, R E; Winget, D E; Sullivan, D; Thompson, Susan E

2009-01-01

We are searching for new pulsating DB white dwarf stars (DBVs) based on the newly found white dwarf stars from the spectra obtained by the Sloan Digital Sky Survey. DBVs pulsate at hotter temperature ranges than their better known cousins, DAVs or ZZ Ceti stars. Since the evolution of white dwarf stars is characterized by cooling, asteroseismological studies of DBVs give us opportunities to study white dwarf structure at a different evolutionary stage than the DAVs. The hottest DBVs are thought to have neutrino luminosities exceeding their photon luminosities (Winget et al. 2004), a quantity measurable through asteroseismology. Therefore, they can also be used to study neutrino physics in the stellar interior. At the time of the meeting, we reported on the nine new DBVs, doubling the number of previously known DBVs. Here we report the new nine pulsators' lightcurves and power spectra.

MEASURING TINY MASS ACCRETION RATES ONTO YOUNG BROWN DWARFS

International Nuclear Information System (INIS)

Herczeg, Gregory J.; Cruz, Kelle L.; Hillenbrand, Lynne A.

2009-01-01

We present low-resolution Keck I/LRIS spectra spanning from 3200 to 9000 A of nine young brown dwarfs and three low-mass stars in the TW Hya Association and in Upper Sco. The optical spectral types of the brown dwarfs range from M5.5 to M8.75, though two have near-IR spectral types of early L dwarfs. We report new accretion rates derived from excess Balmer continuum emission for the low-mass stars TW Hya and Hen 3-600A and the brown dwarfs 2MASS J12073347-3932540, UScoCTIO 128, SSSPM J1102-3431, USco J160606.29-233513.3, DENIS-P J160603.9-205644, and Oph J162225-240515B, and upper limits on accretion for the low-mass star Hen 3-600B and the brown dwarfs UScoCTIO 112, Oph J162225-240515A, and USco J160723.82-221102.0. For the six brown dwarfs in our sample that are faintest at short wavelengths, the accretion luminosity or upper limit is measurable only when the image is binned over large wavelength intervals. This method extends our sensitivity to accretion rate down to ∼10 -13 M sun yr -1 for brown dwarfs. Since the ability to measure an accretion rate from excess Balmer continuum emission depends on the contrast between excess continuum emission and the underlying photosphere, for objects with earlier spectral types the upper limit on accretion rate is much higher. Absolute uncertainties in our accretion rate measurements of ∼3-5 include uncertainty in accretion models, brown dwarf masses, and distance. The accretion rate of 2 x 10 -12 M sun yr -1 onto 2MASS J12073347-3932540 is within 15% of two previous measurements, despite large changes in the Hα flux.

Recent advances on the formation and evolution of white dwarfs

International Nuclear Information System (INIS)

Sion, E.M.

1986-01-01

Advances made in the past seven years in both the theory and observation of white dwarfs which have led to major progress in understanding white dwarf formation and evolution are reviewed. The roles of convective dredge-up, mixing and dilution, accretion, gravitational and thermal diffusion in dense plasmas, radiate forces and mass outflow, nuclear shell burning, diffusion-induced reactions, late thermonuclear shell flashes, rotation, and magnetic fields in white dwarf evolution are considered. Recent work on the properties of white dwarfs in cataclysmic variables is briefly addressed. 153 references

Brown dwarf accretion: Nonconventional star formation over very long timescales

Directory of Open Access Journals (Sweden)

Ćirković Milan M.

2005-01-01

Full Text Available We investigate the process of accretion of interstellar gas by the Galactic population of brown dwarfs over very long timescales typical for physical eschatology. In particular, we use the classical Hoyle-Lyttleton-Bondi accretion model to investigate the rate at which brown dwarfs collect enough additional mass to become red dwarfs, accretion-induced changes in the mass function of the low- mass objects, and the corresponding accretion heating of brown dwarfs. In addition, we show how we can make the definition of the final mass function for stellar objects more precise.

White Dwarf Stars

Science.gov (United States)

1999-01-01

Peering deep inside a cluster of several hundred thousand stars, NASA's Hubble Space Telescope has uncovered the oldest burned-out stars in our Milky Way Galaxy, giving astronomers a fresh reading on the age of the universe. Located in the globular cluster M4, these small, burned-out stars -- called white dwarfs -- are about 12 to 13 billion years old. By adding the one billion years it took the cluster to form after the Big Bang, astronomers found that the age of the white dwarfs agrees with previous estimates that the universe is 13 to 14 billion years old. The images, including some taken by Hubble's Wide Field and Planetary Camera 2, are available online at http://oposite.stsci.edu/pubinfo/pr/2002/10/ or http://www.jpl.nasa.gov/images/wfpc . The camera was designed and built by NASA's Jet Propulsion Laboratory, Pasadena, Calif. In the top panel, a ground-based observatory snapped a panoramic view of the entire cluster, which contains several hundred thousand stars within a volume of 10 to 30 light-years across. The Kitt Peak National Observatory's .9-meter telescope took this picture in March 1995. The box at left indicates the region observed by the Hubble telescope. The Hubble telescope studied a small region of the cluster. A section of that region is seen in the picture at bottom left. A sampling of an even smaller region is shown at bottom right. This region is only about one light-year across. In this smaller region, Hubble pinpointed a number of faint white dwarfs. The blue circles indicate the dwarfs. It took nearly eight days of exposure time over a 67-day period to find these extremely faint stars. Globular clusters are among the oldest clusters of stars in the universe. The faintest and coolest white dwarfs within globular clusters can yield a globular cluster's age. Earlier Hubble observations showed that the first stars formed less than 1 billion years after the universe's birth in the big bang. So, finding the oldest stars puts astronomers within

Confirmation of Faint Dwarf Galaxies in the M81 Group

Science.gov (United States)

Chiboucas, Kristin; Jacobs, Bradley A.; Tully, R. Brent; Karachentsev, Igor D.

2013-11-01

We have followed up on the results of a 65 deg2 CFHT/MegaCam imaging survey of the nearby M81 Group searching for faint and ultra-faint dwarf galaxies. The original survey turned up 22 faint candidate dwarf members. Based on two-color HST ACS/WFC and WFPC2 photometry, we now confirm 14 of these as dwarf galaxy members of the group. Distances and stellar population characteristics are discussed for each. To a completeness limit of M_{r^{\\prime }} = -10, we find a galaxy luminosity function slope of -1.27 ± 0.04 for the M81 Group. In this region, there are now 36 M81 Group members known, including 4 blue compact dwarfs; 8 other late types including the interacting giants M81, NGC 3077, and M82; 19 early type dwarfs; and at least 5 potential tidal dwarf galaxies. We find that the dSph galaxies in M81 appear to lie in a flattened distribution, similar to that found for the Milky Way and M31. One of the newly discovered dSph galaxies has properties similar to the ultra-faint dwarfs being found in the Local Group with a size Re ~ 100 pc and total magnitude estimates M_{r^{\\prime }} = -6.8 and MI ~ -9.1.

The radii and masses of dwarf Cepheids

International Nuclear Information System (INIS)

Fernley, J.A.; Jameson, R.F.; Sherrington, M.R.; Skillen, I.

1987-01-01

The authors present VJK photometry for the dwarf Cepheids CY Aqr, YZ Boo and VZ Cnc, and a radial velocity curve for CY Aqr. Using these data, plus radial velocity curves taken from the literature, Wesselink-type radii, and hence absolute magnitudes and masses, are derived for the three stars. Using these results, plus previously published work, a mean 'pulsation' mass for dwarf Cepheids of 1.2 +-0.3M solar mass is determined. If dwarf Cepheids are early post-main-sequence stars this is less than their 'evolutionary' mass by the ratio Msub(puls)/Msub(evol)approx.0.75. Previously published data on period changes show an order of magnitude larger than predicted by early post-main-sequence evolutionary tracks. The possibility that these stars are at a more advanced evolutionary state is briefly discussed. The properties of fundamental and possible/probable overtone pulsators are compared. Finally attention is drawn to the small cycle-to-cycle variations in dwarf Cepheid light curves noted by many observers and the possible link between these variations and delta Scuti behaviour. (author)

Theoretical models for asteroseismology of DA white dwarf stars

Energy Technology Data Exchange (ETDEWEB)

Bradley, P.A. [XTA, MS B220, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

1996-09-01

Because white dwarfs are the most common end state of stellar evolution, determining their internal structure will yield many clues about the final stages of stellar evolution and the physics of matter under extreme conditions. We present the results of our parametric survey of evolutionary models of compositionally stratified white dwarfs with hydrogen surface layers (DA white dwarfs) and provide a comprehensive set of theoretical {ital g}-mode pulsation periods for comparison to observations of pulsating DA white dwarfs. This survey complements the previous survey of helium atmosphere (DB) white dwarf periods of Bradley, Winget, & Wood. We show how to use the periods of low-overtone and/or trapped modes to constrain the internal structure of pulsating DA white dwarfs by utilizing their sensitivity to the total stellar mass and the location of the hydrogen/helium transition zone. We use G117-B15A as an example to demonstrate the potential of our models for asteroseismology; we suggest that G117-B15A has a mass of 0.55 {ital M}{sub {circle_dot}} and a hydrogen layer mass of {approx_equal}1.5{times}10{sup {minus}4} {ital M}{sub {asterisk}}. {copyright} {ital 1996 The American Astronomical Society.}

Functionally enhanced brown adipose tissue in Ames dwarf mice.

Science.gov (United States)

Darcy, Justin; Bartke, Andrzej

2017-01-02

Reduced insulin-like growth factor 1/insulin signaling (IIS) has been linked to extended longevity in species ranging from yeast to mammals. In mammals, this is exemplified in Ames dwarf (Prop1 df/df ) mice, which have a 40%-60% increase in longevity (males and females, respectively) due to their recessive Prop1 loss-of-function mutation that results in lack of growth hormone (GH), thyroid-stimulating hormone and prolactin. Our laboratory has previously shown that Ames dwarf mice have functionally unique white adipose tissue (WAT) that improves, rather than impairs, insulin sensitivity. Because GH and thyroid hormone are integral to adipose tissue development and function, we hypothesized that brown adipose tissue (BAT) in Ames dwarf mice may also be functionally unique and/or enhanced. Here, we elaborate on our recent findings, which demonstrate that BAT is functionally enhanced in Ames dwarf mice, and suggest that BAT removal in these mice results in utilization of WAT depots as an energy source. We also discuss how our findings compare to those in other long-lived dwarf mice with altered IIS, which unlike Ames dwarf mice, are essentially euthyroid. Lastly, we provide some insights into the implications of these findings and discuss some of the necessary future work in this area.

Nearby Red Dwarfs are Sexy for Planets and Life

Science.gov (United States)

Henry, T. J.; Jao, W.-C.; Subasavage, J. P.; RECONS Team

2005-12-01

The RECONS group continues to discover many nearby red dwarfs in the southern sky through a combination of proper motion surveys, literature review, and ultimately, our parallax program CTIOPI. Already, we have measured the first accurate parallaxes for 11 of the nearest 100 stellar systems, including four within 5 parsecs of the Sun. These nearby red dwarfs are prime candidates for NASA's Space Interferometry Mission (SIM) because the astrometric perturbations are largest for planets orbiting stars of low mass that are nearby. In addition, new multiple red dwarf systems can be targeted for mass determinations, thereby providing points on a comprehensive mass-luminosity relation for the most populous members of the Galaxy. Recent atmospheric modeling of planets orbiting red dwarfs indicates that even if the planets are tidally locked, heat distribution is highly effective in keeping the worlds balmy over the entire surface. Red dwarfs are therefore "back on the table" as viable hosts of life-bearing planets. Given their ubiquity, red dwarfs are being seriously considered as prime SETI targets, and will allow us to answer not only the question "Are We Alone?" but "Just How Alone Are We?" This work has been supported by the National Science Foundation, NASA's Space Interferometry Mission, and Georgia State University.

First report of Raspberry bushy dwarf virus in blackberry in Ecuador

Science.gov (United States)

During the past two decades, several viruses have been identified from Rubus (blackberry and raspberry) in wild and commercial plantings around the world (1) In Ecuador; approximately 14 tons of blackberries (Rubus glaucus) are produced each year in an estimated area of 5,500 hectares. This crop pro...

Simultaneous detection of six stone fruit viruses by non-isotopic molecular hybridization using a unique riboprobe or 'polyprobe'.

Science.gov (United States)

Herranz, M Carmen; Sanchez-Navarro, Jesus A; Aparicio, Frederic; Pallás, Vicente

2005-03-01

A new strategy for the simultaneous detection of plant viruses by molecular hybridization has been developed. Two, four or six viral sequences were fused in tandem and transcribed to render unique riboprobes and designated as 'polyprobes'. The 'polyprobe four' (poly 4) covered the four ilarviruses affecting stone fruit trees including apple mosaic virus (ApMV), prunus necrotic ringspot virus (PNRSV), prune dwarf virus (PDV), and American plum line pattern virus (APLPV) whereas the 'polyprobe two' (poly 2) was designed to detect simultaneously, plum pox virus (PPV) and apple chlorotic leaf spot virus (ACLSV), the two more important viruses affecting these trees. Finally, a 'polyprobe six' (poly 6) was generated to detect any of the six viruses. The three polyprobes were comparable to the individual riboprobes in terms of end-point dilution limit and specificity. The validation of the new simultaneous detection strategy was confirmed by the analysis of 46 field samples from up to seven different hosts collected from 10 different geographical areas.

Suppression of cooling by strong magnetic fields in white dwarf stars.

Science.gov (United States)

Valyavin, G; Shulyak, D; Wade, G A; Antonyuk, K; Zharikov, S V; Galazutdinov, G A; Plachinda, S; Bagnulo, S; Machado, L Fox; Alvarez, M; Clark, D M; Lopez, J M; Hiriart, D; Han, Inwoo; Jeon, Young-Beom; Zurita, C; Mujica, R; Burlakova, T; Szeifert, T; Burenkov, A

2014-11-06

Isolated cool white dwarf stars more often have strong magnetic fields than young, hotter white dwarfs, which has been a puzzle because magnetic fields are expected to decay with time but a cool surface suggests that the star is old. In addition, some white dwarfs with strong fields vary in brightness as they rotate, which has been variously attributed to surface brightness inhomogeneities similar to sunspots, chemical inhomogeneities and other magneto-optical effects. Here we describe optical observations of the brightness and magnetic field of the cool white dwarf WD 1953-011 taken over about eight years, and the results of an analysis of its surface temperature and magnetic field distribution. We find that the magnetic field suppresses atmospheric convection, leading to dark spots in the most magnetized areas. We also find that strong fields are sufficient to suppress convection over the entire surface in cool magnetic white dwarfs, which inhibits their cooling evolution relative to weakly magnetic and non-magnetic white dwarfs, making them appear younger than they truly are. This explains the long-standing mystery of why magnetic fields are more common amongst cool white dwarfs, and implies that the currently accepted ages of strongly magnetic white dwarfs are systematically too young.

White dwarfs, the galaxy and Dirac's cosmology

Energy Technology Data Exchange (ETDEWEB)

Stothers, R [National Aeronautics and Space Administration, Greenbelt, Md. (USA). Goddard Space Flight Center

1976-08-05

Reference is made to the apparent absence, or deficiency, of white dwarfs fainter than about 10/sup -4/L solar mass. An explanation is here proposed on the basis of Dirac's cosmological hypothesis that the gravitational constant, G, has varied with the time elapsed since the beginning of the expansion of the Universe as t/sup -1/ and the number of particles in the Universe has increases as t/sup 2/, if the measurements are made in atomic units. For a white dwarf the Chandrasekhar mass limit is a collection of fundamental constants proportional to Gsup(-3/2) and therefore increases with time as tsup(3/2). In the 'additive' version of Dirac's theory the actual mass, M, of a relatively small object like a star remains essentially unchanged by the creation of new matter in the Universe and hence a white dwarf will become more stable with the course of time; but in the 'multiplicative' version of the theory, M increases as t/sup 2/ and may eventually exceed the Chandrasekhar limit, and if this happens, gravitational collapse of the white dwarf into an invisible black hole or neutron star will quickly occur. It is considered interesting to find whether the 'multiplicative' theory may have a bearing on the apparent deficiency of faint white dwarfs, and to consider whether there are any possible consequences for galactic evolution. This is here discussed.

Solo dwarfs I: survey introduction and first results for the Sagittarius dwarf irregular galaxy

Science.gov (United States)

Higgs, C. R.; McConnachie, A. W.; Irwin, M.; Bate, N. F.; Lewis, G. F.; Walker, M. G.; Côté, P.; Venn, K.; Battaglia, G.

2016-05-01

We introduce the Solitary Local dwarfs survey (Solo), a wide-field photometric study targeting every isolated dwarf galaxy within 3 Mpc of the Milky Way. Solo is based on (u)gi multiband imaging from Canada-France-Hawaii Telescope/MegaCam for northern targets, and Magellan/Megacam for southern targets. All galaxies fainter than MV ≃ -18 situated beyond the nominal virial radius of the Milky Way and M31 (≳300 kpc) are included in this volume-limited sample, for a total of 42 targets. In addition to reviewing the survey goals and strategy, we present results for the Sagittarius dwarf irregular galaxy (Sag DIG), one of the most isolated, low-mass galaxies, located at the edge of the Local Group. We analyse its resolved stellar populations and their spatial distributions. We provide updated estimates of its central surface brightness and integrated luminosity, and trace its surface brightness profile to a level fainter than 30 mag arcsec-2. Sag DIG is well described by a highly elliptical (disc-like) system following a single component Sérsic model. However, a low-level distortion is present at the outer edges of the galaxy that, were Sag DIG not so isolated, would likely be attributed to some kind of previous tidal interaction. Further, we find evidence of an extremely low level, extended distribution of stars beyond ˜5 arcmin (>1.5 kpc) that suggests Sag DIG may be embedded in a very low-density stellar halo. We compare the stellar and H I structures of Sag DIG, and discuss results for this galaxy in relation to other isolated, dwarf irregular galaxies in the Local Group.

Survival of a brown dwarf after engulfment by a red giant star.

Science.gov (United States)

Maxted, P F L; Napiwotzki, R; Dobbie, P D; Burleigh, M R

2006-08-03

Many sub-stellar companions (usually planets but also some brown dwarfs) orbit solar-type stars. These stars can engulf their sub-stellar companions when they become red giants. This interaction may explain several outstanding problems in astrophysics but it is unclear under what conditions a low mass companion will evaporate, survive the interaction unchanged or gain mass. Observational tests of models for this interaction have been hampered by a lack of positively identified remnants-that is, white dwarf stars with close, sub-stellar companions. The companion to the pre-white dwarf AA Doradus may be a brown dwarf, but the uncertain history of this star and the extreme luminosity difference between the components make it difficult to interpret the observations or to put strong constraints on the models. The magnetic white dwarf SDSS J121209.31 + 013627.7 may have a close brown dwarf companion but little is known about this binary at present. Here we report the discovery of a brown dwarf in a short period orbit around a white dwarf. The properties of both stars in this binary can be directly observed and show that the brown dwarf was engulfed by a red giant but that this had little effect on it.

Observations of M dwarfs beyond 2.2 μm

International Nuclear Information System (INIS)

Berriman, G.

1987-01-01

This paper presents the first systematic spectroscopic observations of M dwarfs beyond 2.2μm. The coolest dwarfs show strong water absorption in the 3μm window, and beyond 4μm, the energy distributions of all the stars fall slightly less steeply than the Rayleigh-Jeans tail of a blackbody. Spectra between 1 and 4μm are essential in deriving accurate luminosities of M dwarfs, and possibly in deriving accurate effective temperatures too. New values reported here are not in general well explained by theoretical models of hydrogen burning stars. This is especially true for those cooler than 3000K: in the HR diagram they lie closer to brown dwarfs, in contrast to recent results based only on photometry. (author)

Spatial delayed nonmatching-to-sample performances in long-living Ames dwarf mice.

Science.gov (United States)

Derenne, Adam; Brown-Borg, Holly M; Martner, Sarah; Wolff, Wendy; Frerking, Morgan

2014-01-17

Ames dwarf mice have an extended lifespan by comparison with normal mice. Behavioral testing has revealed that sometimes Ames dwarf mice also evince superior performances relative to normal mice, but in other cases they do not. In this experiment, Ames dwarf and normal mice were compared on a T-maze test and on a delayed nonmatching-to-sample variant of a T-maze test. On the simple T-maze, Ames dwarf and normal mice committed comparable numbers of errors. On the nonmatching-to-sample task, normal mice mastered the discrimination by the end of the experiment while Ames dwarf mice did not. The apparatus, distances traveled and session duration were equivalent between the two tasks. The poorer performances of Ames dwarf mice on the nonmatching-to-sample task suggests that Ames dwarf mice may not be as capable of learning relatively cognitively complex tasks as normal mice. © 2013.

On the masses of the white dwarfs in cataclysmic variables

International Nuclear Information System (INIS)

Livio, M.; Soker, N.

1984-01-01

The question of the masses of the white dwarfs in cataclysmic binaries is examined. It is shown that selection effects can explain an overabundance of massive white dwarfs in novae but not in dwarf novae. It is proposed that the spiralling-in process in the common envelope favours the formation of more massive white dwarfs A number of simplified spiralling-in calculations are performed. The calculations demonstrate that the probability of coalescence of the secondary with the primary core, or secondary dissipation, is higher in the case of a giant envelope than in the case of a super giant envelope. Consequently, binaries with primary core masses greater than approx. 0.7 Msolar masses (and thus massive white dwarf remnants), have a better chance of surviving common envelope evolution and are therefore better candidates for the formation of cataclysmic variables. (author)

Charged condensate and helium dwarf stars

Energy Technology Data Exchange (ETDEWEB)

Gabadadze, Gregory; Rosen, Rachel A, E-mail: gg32@nyu.edu, E-mail: rar339@nyu.edu [Center for Cosmology and Particle Physics, Department of Physics, New York University, New York, NY 10003 (United States)

2008-10-15

White dwarf stars composed of carbon, oxygen and heavier elements are expected to crystallize as they cool down below certain temperatures. Yet, simple arguments suggest that the helium white dwarf cores may not solidify, mostly because of zero-point oscillations of the helium ions that would dissolve the crystalline structure. We argue that the interior of the helium dwarfs may instead form a macroscopic quantum state in which the charged helium-4 nuclei are in a Bose-Einstein condensate, while the relativistic electrons form a neutralizing degenerate Fermi liquid. We discuss the electric charge screening, and the spectrum of this substance, showing that the bosonic long-wavelength fluctuations exhibit a mass gap. Hence, there is a suppression at low temperatures of the boson contribution to the specific heat-the latter being dominated by the specific heat of the electrons near the Fermi surface. This state of matter may have observational signatures.

Molecular characterization of a virus from the family Luteoviridae associated with cotton blue disease.

Science.gov (United States)

Corrêa, R L; Silva, T F; Simões-Araújo, J L; Barroso, P A V; Vidal, M S; Vaslin, M F S

2005-07-01

Cotton blue disease is an aphid-transmitted cotton disease described in Brazil in 1962 as Vein Mosaic "var. Ribeirão Bonito". At present it causes economically important losses in cotton crops if control measures are not implemented. The observed symptoms and mode of transmission have prompted researchers to speculate that cotton blue disease could be attributed to a member of the family Luteoviridae, but there was no molecular evidence supporting this hypothesis. We have amplified part of the genome of a virus associated with this disease using degenerate primers for members of the family Luteoviridae. Sequence analysis of the entire capsid and a partial RdRp revealed a virus probably belonging to the genus Polerovirus. Based on our results we propose that cotton blue disease is associated with a virus with the putative name Cotton leafroll dwarf virus (CLRDV).

Explaining millimeter-sized particles in brown dwarf disks

NARCIS (Netherlands)

Pinilla, P.; Birnstiel, T.; Benisty, M.; Ricci, L.; Natta, A.; Dullemond, C.P.; Dominik, C.; Testi, L.

2013-01-01

Context. Planets have been detected around a variety of stars, including low-mass objects, such as brown dwarfs. However, such extreme cases are challenging for planet formation models. Recent sub-millimeter observations of disks around brown dwarf measured low spectral indices of the continuum

The population of single and binary white dwarfs of the Galactic bulge

Science.gov (United States)

Torres, S.; García-Berro, E.; Cojocaru, R.; Calamida, A.

2018-05-01

Recent Hubble Space Telescope observations have unveiled the white dwarf cooling sequence of the Galactic bulge. Although the degenerate sequence can be well fitted employing the most up-to-date theoretical cooling sequences, observations show a systematic excess of red objects that cannot be explained by the theoretical models of single carbon-oxygen white dwarfs of the appropriate masses. Here, we present a population synthesis study of the white dwarf cooling sequence of the Galactic bulge that takes into account the populations of both single white dwarfs and binary systems containing at least one white dwarf. These calculations incorporate state-of-the-art cooling sequences for white dwarfs with hydrogen-rich and hydrogen-deficient atmospheres, for both white dwarfs with carbon-oxygen and helium cores, and also take into account detailed prescriptions of the evolutionary history of binary systems. Our Monte Carlo simulator also incorporates all the known observational biases. This allows us to model with a high degree of realism the white dwarf population of the Galactic bulge. We find that the observed excess of red stars can be partially attributed to white dwarf plus main sequence binaries, and to cataclysmic variables or dwarf novae. Our best fit is obtained with a higher binary fraction and an initial mass function slope steeper than standard values, as well as with the inclusion of differential reddening and blending. Our results also show that the possible contribution of double degenerate systems or young and thick-discbulge stars is negligible.

A METHANE IMAGING SURVEY FOR T DWARF CANDIDATES IN ρ OPHIUCHI

International Nuclear Information System (INIS)

Haisch, Karl E.; Barsony, Mary; Tinney, Chris

2010-01-01

We report on the results of the first deep, wide-field, near-infrared methane imaging survey of the ρ Ophiuchi cloud core to search for T dwarfs. Among the 6587 objects detected, 22 were identified as T dwarf candidates. Brown dwarf models indicate that at the age and distance of the ρ Ophiuchi cloud, these T dwarf candidates have masses between 1 and 2 Jupiter masses. If confirmed as genuine T dwarfs, these objects would be the youngest, lowest mass, and lowest gravity free-floating objects ever directly observed. The existence of these candidates suggests that the initial mass function of the ρ Ophiuchi cloud extends well into the regime of planetary mass objects. A large fraction (59% ± 16%) of our T dwarf candidates appear to be surrounded by circumstellar disks, and thus represents the lowest mass objects yet found to harbor circumstellar disks.

On the Stability of Strange Dwarf Hybrid Stars

Energy Technology Data Exchange (ETDEWEB)

Alford, Mark G.; Harris, Steven P. [Physics Department, Washington University, St. Louis, MO 63130 (United States); Sachdeva, Pratik S., E-mail: harrissp@wustl.edu [Department of Physics, University of California, Berkeley, CA 94720 (United States)

2017-10-01

We investigate the stability of “strange dwarfs”: white-dwarf-sized stars with a density discontinuity between a small dense core of quark matter and a thick low-density mantle of degenerate electrons. Previous work on strange dwarfs suggested that such a discontinuity could stabilize stars that would have been classified as unstable by the conventional criteria based on extrema in the mass–radius relation. We investigate the stability of such stars by numerically solving the Sturm–Liouville equations for the lowest-energy modes of the star. We find that the conventional criteria are correct, and strange dwarfs are not stable.

QCD matter in white dwarfs and supernova collapse

International Nuclear Information System (INIS)

Mathews, Grant J.; Meixner, M.; Lan, N.Q.; Suh, I.-S.

2010-01-01

The search for astrophysical evidence for a transition to QCD matter is an important goal. Although much effort has gone into searching for neutron star candidates, here we describe the exploration of two other possible signatures. One is the search for strange dwarfs. Masses and radii for a large number of white dwarfs have been deduced from a combination of proper motion studies, Hipparcos parallax distances, effective temperatures, and binary or spectroscopic masses. Some stars appear to have radii which are significantly smaller than that expected for a standard electron-degenerate white-dwarf equation of state. We argue that there is marginal evidence for bimodality in the radius distribution. We show that the data exhibit several features consistent with the expected mass-radius relation of strange dwarfs. We identify eight nearby white dwarfs that are possible candidates for strange matter cores and suggest observational tests of this hypothesis. We also review the current status of core-collapse supernova research, and in particular, the effects on the explosion of a QCD phase transition in the proto-neutron-star core. We describe how a first order transition could enhance the explosion and lead to observable effects in the emergent neutrino light curve. (author)

CONFIRMATION OF FAINT DWARF GALAXIES IN THE M81 GROUP

Energy Technology Data Exchange (ETDEWEB)

Chiboucas, Kristin [Gemini Observatory, 670 North A' ohoku Pl, Hilo, HI 96720 (United States); Jacobs, Bradley A.; Tully, R. Brent [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96821 (United States); Karachentsev, Igor D., E-mail: kchibouc@gemini.edu, E-mail: bjacobs@ifa.hawaii.edu, E-mail: tully@ifa.hawaii.edu, E-mail: ikar@luna.sao.ru [Special Astrophysical Observatory (SAO), Russian Academy of Sciences, Nizhnij Arkhyz, Karachai-Cherkessian Republic 369167 (Russian Federation)

2013-11-01

We have followed up on the results of a 65 deg{sup 2} CFHT/MegaCam imaging survey of the nearby M81 Group searching for faint and ultra-faint dwarf galaxies. The original survey turned up 22 faint candidate dwarf members. Based on two-color HST ACS/WFC and WFPC2 photometry, we now confirm 14 of these as dwarf galaxy members of the group. Distances and stellar population characteristics are discussed for each. To a completeness limit of M{sub r{sup '}}= -10, we find a galaxy luminosity function slope of –1.27 ± 0.04 for the M81 Group. In this region, there are now 36 M81 Group members known, including 4 blue compact dwarfs; 8 other late types including the interacting giants M81, NGC 3077, and M82; 19 early type dwarfs; and at least 5 potential tidal dwarf galaxies. We find that the dSph galaxies in M81 appear to lie in a flattened distribution, similar to that found for the Milky Way and M31. One of the newly discovered dSph galaxies has properties similar to the ultra-faint dwarfs being found in the Local Group with a size R{sub e} ∼ 100 pc and total magnitude estimates M{sub r{sup '}}= -6.8 and M{sub I} ∼ –9.1.

Short-range effects in large white dwarfs

International Nuclear Information System (INIS)

Membrado, M.C.; Pacheco, A.F.

1988-01-01

Recent work of Membrado and Pacheco (1988) on the implication of Yukawa-like effects in small white dwarfs is extended to analyze the very massive case. Although the role of these impurities grows substantially as the radius of the star decreases, when reasonable supergravity parameters are used the predicted change in the white dwarf mass-radius relation is unobservably small. 8 references

The Missing Link: Early Methane ("T") Dwarfs in the Sloan Digital Sky Survey.

Science.gov (United States)

Leggett; Geballe; Fan; Schneider; Gunn; Lupton; Knapp; Strauss; McDaniel; Golimowski; Henry; Peng; Tsvetanov; Uomoto; Zheng; Hill; Ramsey; Anderson; Annis; Bahcall; Brinkmann; Chen; Csabai; Fukugita; Hennessy; Hindsley; Ivezic; Lamb; Munn; Pier; Schlegel; Smith; Stoughton; Thakar; York

2000-06-10

We report the discovery of three cool brown dwarfs that fall in the effective temperature gap between the latest L dwarfs currently known, with no methane absorption bands in the 1-2.5 µm range, and the previously known methane (T) dwarfs, whose spectra are dominated by methane and water. The newly discovered objects were detected as very red objects in the Sloan Digital Sky Survey imaging data and have JHK colors between the red L dwarfs and the blue Gl 229B-like T dwarfs. They show both CO and CH(4) absorption in their near-infrared spectra in addition to H(2)O, with weaker CH(4) absorption features in the H and K bands than those in all other methane dwarfs reported to date. Due to the presence of CH(4) in these bands, we propose that these objects are early T dwarfs. The three form part of the brown dwarf spectral sequence and fill in the large gap in the overall spectral sequence from the hottest main-sequence stars to the coolest methane dwarfs currently known.

White Dwarfs in Cataclysmic Variables: An Update

Directory of Open Access Journals (Sweden)

E. M. Sion

2015-02-01

Full Text Available In this review, we summarize what is currently known about the surface temperatures of accreting white dwarfs in nonmagnetic and magnetic cataclysmic variables (CVs based upon synthetic spectral analyses of far ultraviolet data. We focus only on white dwarf surface temperatures, since in the area of chemical abundances, rotation rates, WD masses and accretion rates, relatively little has changed since our last review, pending the results of a large HST GO programinvolving 48 CVs of different CV types. The surface temperature of the white dwarf in SS Cygni is re-examined in the light of its revised distance. We also discuss new HST spectra of the recurrent nova T Pyxidis as it transitioned into quiescence following its April 2011 nova outburst.

THE INITIAL-FINAL MASS RELATION AMONG WHITE DWARFS IN WIDE BINARIES

International Nuclear Information System (INIS)

Zhao, J. K.; Oswalt, T. D.; Willson, L. A.; Wang, Q.; Zhao, G.

2012-01-01

We present the initial-final mass relation derived from 10 white dwarfs in wide binaries that consist of a main-sequence star and a white dwarf. The temperature and gravity of each white dwarf were measured by fitting theoretical model atmospheres to the observed spectrum using a χ 2 fitting algorithm. The cooling time and mass were obtained using theoretical cooling tracks. The total age of each binary was estimated from the chromospheric activity of its main-sequence component to an uncertainty of about 0.17 dex in log t. The difference between the total age and white dwarf cooling time is taken as the main-sequence lifetime of each white dwarf. The initial mass of each white dwarf was then determined using stellar evolution tracks with a corresponding metallicity derived from spectra of their main-sequence companions, thus yielding the initial-final mass relation. Most of the initial masses of the white dwarf components are between 1 and 2 M ☉ . Our results suggest a correlation between the metallicity of a white dwarf's progenitor and the amount of post-main-sequence mass loss it experiences—at least among progenitors with masses in the range of 1-2 M ☉ . A comparison of our observations to theoretical models suggests that low-mass stars preferentially lose mass on the red giant branch.

Carbon-enhanced metal-poor stars in dwarf galaxies

NARCIS (Netherlands)

Salvadori, Stefania; Skúladóttir, Ása; Tolstoy, Eline

2015-01-01

We investigate the frequency and origin of carbon-enhanced metal-poor (CEMP) stars in Local Group dwarf galaxies by means of a statistical, data-calibrated cosmological model for the hierarchical build-up of the Milky Way and its dwarf satellites. The model self-consistently explains the variation

The POKEMON Speckle Survey of Nearby M-Dwarfs

Science.gov (United States)

van Belle, Gerard; von Braun, Kaspar; Horch, Elliott; Clark, Catherine; DSSI Speckle Team

2018-01-01

The POKEMON (Pervasive Overview of Kompanions of Every M-dwarf in Our Neighborhood) survey of nearby M-dwarfs intends to inspect, at diffraction-limited resolution, every low-mass star out to 15pc, along with selected additional objects to 25pc. The primary emphasis of the survey is detection of low-mass companions to these M-dwarfs for refinement of the low-mass star multiplicity rate. The resultant catalog of M-dwarf companions will also guide immediate refinement of transit planet detection results from surveys such as TESS. POKEMON is using Lowell Observatory's 4.3-m Discovery Channel Telescope (DCT) with the Differential Speckle Survey Instrument (DSSI) speckle camera, along with the NN-Explore Exoplanet Stellar Speckle Imager (NESSI) speckle imager on 3.5-m WIYN; the survey takes advantage of the extremely rapid observing cadence rates possible with WIYN and (especially) DCT. The current status and preliminary results from the first 20+ nights of observing will be presented. Gotta observe them all!

Effective field theory for quantum liquid in dwarf stars

Energy Technology Data Exchange (ETDEWEB)

Gabadadze, Gregory [Center for Cosmology and Particle Physics, Department of Physics, New York University, 4 Washington Place, New York, NY 10003 (United States); Rosen, Rachel A., E-mail: gg32@nyu.edu, E-mail: rarosen@physik.su.se [Oskar Klein Centre for Cosmoparticle Physics, Department of Physics, Stockholm University, AlbaNova, Roslagstullsbacken 21, SE - 106 91, Stockholm (Sweden)

2010-04-01

An effective field theory approach is used to describe quantum matter at greater-than-atomic but less-than-nuclear densities which are encountered in white dwarf stars. We focus on the density and temperature regime for which charged spin-0 nuclei form an interacting charged Bose-Einstein condensate, while the neutralizing electrons form a degenerate fermi gas. After a brief introductory review, we summarize distinctive properties of the charged condensate, such as a mass gap in the bosonic sector as well as gapless fermionic excitations. Charged impurities placed in the condensate are screened with great efficiency, greater than in an equivalent uncondensed plasma. We discuss a generalization of the Friedel potential which takes into account bosonic collective excitations in addition to the fermionic excitations. We argue that the charged condensate could exist in helium-core white dwarf stars and discuss the evolution of these dwarfs. Condensation would lead to a significantly faster rate of cooling than that of carbon- or oxygen-core dwarfs with crystallized cores. This prediction can be tested observationally: signatures of charged condensation may have already been seen in the recently discovered sequence of helium-core dwarfs in the nearby globular cluster NGC 6397. Sufficiently strong magnetic fields can penetrate the condensate within Abrikosov-like vortices. We find approximate analytic vortex solutions and calculate the values of the lower and upper critical magnetic fields at which vortices are formed and destroyed respectively. The lower critical field is within the range of fields observed in white dwarfs, but tends toward the higher end of this interval. This suggests that for a significant fraction of helium-core dwarfs, magnetic fields are entirely expelled within the core.

Sagittarius Dwarf Galaxy

Science.gov (United States)

Ibata, R.; Murdin, P.

2000-11-01

The Sagittarius DWARF GALAXY is the closest member of the Milky Way's entourage of satellite galaxies. Discovered by chance in 1994, its presence had previously been overlooked because it is largely hidden by the most crowded regions of our own Galaxy with which it is merging....

The stellar content of the isolated transition dwarf galaxy DDO210

NARCIS (Netherlands)

McConnachie, Alan W.; Arimoto, Nobuo; Irwin, Mike; Tolstoy, Eline

2006-01-01

We use Subaru Suprime-Cam and VLT FORS1 photometry of the dwarf galaxy DDO210 to study the global stellar content and structural properties of a transition-type galaxy (with properties intermediate between dwarf irregular and dwarf spheroidal systems). This galaxy is sufficiently isolated that tidal

POLARIMETRIC DETECTION OF EXOPLANETS TRANSITING T AND L BROWN DWARFS

International Nuclear Information System (INIS)

Sengupta, Sujan

2016-01-01

While scattering of light by atoms and molecules yields large amounts of polarization at the B-band of both T and L dwarfs, scattering by dust grains in the cloudy atmosphere of L dwarfs gives rise to significant polarization at the far-optical and infrared wavelengths where these objects are much brighter. However, the observable disk-averaged polarization should be zero if the clouds are uniformly distributed and the object is spherically symmetric. Therefore, in order to explain the observed large polarization of several L dwarfs, rotation-induced oblateness or horizontally inhomogeneous cloud distribution in the atmosphere is invoked. On the other hand, when an extra-solar planet of Earth-size or larger transits the brown dwarf along the line of sight, the asymmetry induced during the transit gives rise to a net non-zero, time-dependent polarization. Employing atmospheric models for a range of effective temperature and surface gravity appropriate for T and L dwarfs, I derive the time-dependent polarization profiles of these objects during the transit phase and estimate the peak amplitude of polarization that occurs during the inner contact points of the transit ingress/egress phase. It is found that peak polarization in the range of 0.2%–1.0% at I and J band may arise of cloudy L dwarfs occulted by Earth-size or larger exoplanets. Such an amount of polarization is higher than what can be produced by rotation-induced oblateness of even rapidly rotating L dwarfs. Hence, I suggest that time-resolved imaging polarization could be a potential technique for detecting transiting exoplanets around L dwarfs.

POLARIMETRIC DETECTION OF EXOPLANETS TRANSITING T AND L BROWN DWARFS

Energy Technology Data Exchange (ETDEWEB)

Sengupta, Sujan, E-mail: sujan@iiap.res.in [Indian Institute of Astrophysics, Koramangala 2nd Block, Bangalore 560 034 (India)

2016-10-01

While scattering of light by atoms and molecules yields large amounts of polarization at the B-band of both T and L dwarfs, scattering by dust grains in the cloudy atmosphere of L dwarfs gives rise to significant polarization at the far-optical and infrared wavelengths where these objects are much brighter. However, the observable disk-averaged polarization should be zero if the clouds are uniformly distributed and the object is spherically symmetric. Therefore, in order to explain the observed large polarization of several L dwarfs, rotation-induced oblateness or horizontally inhomogeneous cloud distribution in the atmosphere is invoked. On the other hand, when an extra-solar planet of Earth-size or larger transits the brown dwarf along the line of sight, the asymmetry induced during the transit gives rise to a net non-zero, time-dependent polarization. Employing atmospheric models for a range of effective temperature and surface gravity appropriate for T and L dwarfs, I derive the time-dependent polarization profiles of these objects during the transit phase and estimate the peak amplitude of polarization that occurs during the inner contact points of the transit ingress/egress phase. It is found that peak polarization in the range of 0.2%–1.0% at I and J band may arise of cloudy L dwarfs occulted by Earth-size or larger exoplanets. Such an amount of polarization is higher than what can be produced by rotation-induced oblateness of even rapidly rotating L dwarfs. Hence, I suggest that time-resolved imaging polarization could be a potential technique for detecting transiting exoplanets around L dwarfs.

An Intermediate-Mass Black Hole in the Dwarf Galaxy Pox 52

Science.gov (United States)

Barth, Aaron

Do dwarf elliptical and dwarf spiral galaxies contain central black holes with masses below 106 solar masses? Beyond the Local Group dynamical searches for black holes in this mass range are very difficult but the detection of accretion-powered nuclear activity could be used to infer the presence of a black hole. The nearby dwarf spiral galaxy NGC 4395 hosts a faint Seyfert 1 nucleus with a likely black hole mass in the range 104-105 solar masses and for more than a decade it has been the only known example of a Seyfert 1 nucleus in a dwarf galaxy. I will present new Keck spectra of the dwarf galaxy POX 52 which demonstrate that it has a Seyfert 1 spectrum nearly identical to that of NGC 4395. Its velocity dispersion is 37 km/s suggesting a possible black hole mass of order 105 solar masses. I will discuss the prospects for systematic searches for nuclear activity in dwarf galaxies and the implications for black hole demographics.

An overview of white dwarf stars

OpenAIRE

Fontaine, Gilles; Brassard, Pierre; Charpinet, Stéphane; Randall, Suzanna K.; Van Grootel, Valérie

2013-01-01

We present a brief summary of what is currently known about white dwarf stars, with an emphasis on their evolutionary and internal properties. As is well known, white dwarfs represent the end products of stellar evolution for the vast majority of stars and, as such, bear the signatures of past events (such as mass loss, mixing phases, loss and redistribution of angular momentum, and thermonuclear burning) that are of essential importance in the evolution of stars in general. In addition, whit...

A wave model for dwarf novae

International Nuclear Information System (INIS)

Sparks, W.M.; Kutter, G.S.

1980-01-01

The rapid coherent oscillation during a dwarf nova outburst is attributed to an accretion-driven wave going around the white dwarf component of the binary system. The increase and decrease in the period of this oscillation is due to the change in the velocity of the wave as it is first being driven and then damped. Qualitatively, a large number of observations can be explained with such a model. The beginnings of a mathematical representation of this model are developed. (orig.)

Pulsations in white dwarfs: Selected topics

Directory of Open Access Journals (Sweden)

Saio H.

2013-03-01

Full Text Available This paper presents a very brief overview of the observed properties of g-mode pulsations in variable white dwarfs. We then discuss a few selected topics: Excitation mechanisms (kappa- and convection- mechanisms, and briefly the effect of a strong magnetic field (∼ 1 MG on g-modes as recently found in a hot DQ (carbon-rich atmosphere white dwarf. In the discussion of excitation mechanisms, a simple interpretation for the convection mechanism is given.

UBV photometry of dwarf novae in the brightness minimum

International Nuclear Information System (INIS)

Voloshina, I.B.; Lyutyj, V.M.

1983-01-01

Photoelectric one-night observations of the dwarf novae SS Cyg at minimum light evidence for the existence of eclipses in this system at the moments of conjuctions. The orbital inclination of the system is estimated to be i approximately 70 deg C. The components of this system are low-massive (white and red dwarf stars) and low-luminous objects. As the optical luminosity of the dwarf novae at the minimum light is dependent on the accretion disk and hot spot at its periphery, where the substance jet run out from a nondegenerated component falls, eclipses should be associated with the disk and hot spot. The white dwarf star contributes greatly to the luminosity at the minimum light, but its eclipses are possible only at i approximately 90 deg

The dwarf spheroidal galaxies around the milky way

NARCIS (Netherlands)

Tolstoy, E.; Battaglia, G.; Helmi, A.; Irwin, M. J.; Hill, V.; Vallenari, A; Tantalo, R; Portinari, L; Moretti, A

2007-01-01

We review the progress of ESO/WFI Imaging and VLT/FLAMES spectroscopy of large numbers of individual stars in nearby dwarf spheroidal galaxies by the Dwarf Abundances and Radial-velocities Team (DART). These observations have allowed us to show that neither the kinematics nor the abundance nor the

THE COLDEST BROWN DWARF (OR FREE-FLOATING PLANET)?: THE Y DWARF WISE 1828+2650

International Nuclear Information System (INIS)

Beichman, C.; Gelino, Christopher R.; Kirkpatrick, J. Davy; Marsh, Kenneth A.; Barman, Travis S.; Cushing, Michael C.; Wright, E. L.

2013-01-01

We have monitored the position of the cool Y dwarf WISEPA J182831.08+265037.8 using a combination of ground- and space-based telescopes and have determined its distance to be 11.2 +1.3 –1.0 pc. Its absolute H magnitude, M H = 22.21 +0.25 –0.22 mag, suggests a mass in the range 0.5-20 M Jup for ages of 0.1-10 Gyr with an effective temperature in the range 250-400 K. The broad range in mass is due primarily to the unknown age of the object. Since the high tangential velocity of the object, 51 ± 5 km s –1 , is characteristic of an old disk population, a plausible age range of 2-4 Gyr leads to a mass range of 3-6 M Jup based on fits to the (highly uncertain) COND evolutionary models. The range in temperature is due to the fact that no single model adequately represents the 1-5 μm spectral energy distribution (SED) of the source, failing by factors of up to five at either the short or long wavelength portions of the SED. The appearance of this very cold object may be affected by non-equilibrium chemistry or low temperature condensates forming clouds, two atmospheric processes that are known to be important in brown dwarf atmospheres but have proven difficult to model. Finally, we argue that there would have to be a very steep upturn in the number density of late-type Y-dwarfs to account for the putative population of objects suggested by recent microlensing observations. Whether WISE 1828+2650 sits at the low-mass end of the brown dwarf population or is the first example of a large number of 'free-floating' planets is not yet known.

ENERGY DISSIPATION THROUGH QUASI-STATIC TIDES IN WHITE DWARF BINARIES

International Nuclear Information System (INIS)

Willems, B.; Deloye, C. J.; Kalogera, V.

2010-01-01

We present a formalism to study tidal interactions in white dwarf binaries in the limiting case of quasi-static tides, in which the tidal forcing frequencies are small, compared to the inverse of the white dwarf's dynamical timescale. The formalism is valid for arbitrary orbital eccentricities and therefore applicable to white dwarf binaries in the Galactic disk as well as globular clusters. In the quasi-static limit, the total perturbation of the gravitational potential shows a phase shift with respect to the position of the companion, the magnitude of which is determined primarily by the efficiency of energy dissipation through convective damping. We determine rates of secular evolution of the orbital elements and white dwarf rotational angular velocity for a 0.3 M sun helium white dwarf in binaries with orbital frequencies in the Laser Interferometer Space Antenna (LISA) gravitational wave frequency band and companion masses ranging from 0.3 M sun to 10 5 M sun . The resulting tidal evolution timescales for the orbital semimajor axis are longer than a Hubble time, so that convective damping of quasi-static tides need not be considered in the construction of gravitational wave templates of white dwarf binaries in the LISA band. Spin-up of the white dwarf, on the other hand, can occur on timescales of less than 10 Myr, provided that the white dwarf is initially rotating with a frequency much smaller than the orbital frequency. For semi-detached white dwarf binaries spin-up can occur on timescales of less than 1 Myr. Nevertheless, the timescales remain longer than the orbital inspiral timescales due to gravitational radiation, so that the degree of asynchronism in these binaries increases. As a consequence, tidal forcing eventually occurs at forcing frequencies beyond the quasi-static tide approximation. For the shortest period binaries, energy dissipation is therefore expected to take place through dynamic tides and resonantly excited g-modes.

THE HAWAII INFRARED PARALLAX PROGRAM. II. YOUNG ULTRACOOL FIELD DWARFS

Energy Technology Data Exchange (ETDEWEB)

Liu, Michael C. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Dupuy, Trent J. [The University of Texas at Austin, Department of Astronomy, 2515 Speedway C1400, Austin, TX 78712 (United States); Allers, Katelyn N., E-mail: mliu@ifa.hawaii.edu [Department of Physics and Astronomy, Bucknell University, Lewisburg, PA 17837 (United States)

2016-12-10

We present a large, uniform analysis of young (≈10–150 Myr) ultracool dwarfs, based on new high-precision infrared (IR) parallaxes for 68 objects. We find that low-gravity (vl-g) late-M and L dwarfs form a continuous sequence in IR color–magnitude diagrams, separate from the field population and from current theoretical models. These vl-g objects also appear distinct from young substellar (brown dwarf and exoplanet) companions, suggesting that the two populations may have a different range of physical properties. In contrast, at the L/T transition, young, old, and spectrally peculiar objects all span a relatively narrow range in near-IR absolute magnitudes. At a given spectral type, the IR absolute magnitudes of young objects can be offset from ordinary field dwarfs, with the largest offsets occurring in the Y and J bands for late-M dwarfs (brighter than the field) and mid-/late-L dwarfs (fainter than the field). Overall, low-gravity (vl-g) objects have the most uniform photometric behavior, while intermediate gravity (int-g) objects are more diverse, suggesting a third governing parameter beyond spectral type and gravity class. We examine the moving group membership for all young ultracool dwarfs with parallaxes, changing the status of 23 objects (including 8 previously identified planetary-mass candidates) and fortifying the status of another 28 objects. We use our resulting age-calibrated sample to establish empirical young isochrones and show a declining frequency of vl-g objects relative to int-g objects with increasing age. Notable individual objects in our sample include high-velocity (≳100 km s{sup −1}) int-g objects, very red late-L dwarfs with high surface gravities, candidate disk-bearing members of the MBM20 cloud and β  Pic moving group, and very young distant interlopers. Finally, we provide a comprehensive summary of the absolute magnitudes and spectral classifications of young ultracool dwarfs, using a combined sample of 102�

Angular momentum of dwarf galaxies

Science.gov (United States)

Kurapati, Sushma; Chengalur, Jayaram N.; Pustilnik, Simon; Kamphuis, Peter

2018-05-01

Mass and specific angular momentum are two fundamental physical parameters of galaxies. We present measurements of the baryonic mass and specific angular momentum of 11 void dwarf galaxies derived from neutral hydrogen (HI) synthesis data. Rotation curves were measured using 3D and 2D tilted ring fitting routines, and the derived curves generally overlap within the error bars, except in the central regions where, as expected, the 3D routines give steeper curves. The specific angular momentum of void dwarfs is found to be high compared to an extrapolation of the trends seen for higher mass bulge-less spirals, but comparable to that of other dwarf irregular galaxies that lie outside of voids. As such, our data show no evidence for a dependence of the specific angular momentum on the large scale environment. Combining our data with the data from the literature, we find a baryonic threshold of ˜109.1 M⊙ for this increase in specific angular momentum. Interestingly, this threshold is very similar to the mass threshold below which the galaxy discs start to become systematically thicker. This provides qualitative support to the suggestion that the thickening of the discs, as well as the increase in specific angular momentum, are both results of a common physical mechanism, such as feedback from star formation. Quantitatively, however, the amount of star formation observed in our dwarfs appears insufficient to produce the observed increase in specific angular momentum. It is hence likely that other processes, such as cold accretion of high angular momentum gas, also play a role in increasing the specific angular momentum.

Genetic Drift. The ancient Egyptian dwarfs of the Walters Art Museum.

Science.gov (United States)

Kozma, Chahira

2010-10-01

The ancient Egyptians left an impressive artistic legacy documenting many aspects of their society including the existence of dwarfs as highly valued members. In previous publications in the Journal, I discussed dwarfs and skeletal dysplasia in ancient Egypt. In this study, I examined the ancient Egyptian representations of dwarfs of the Walters Art Museum in Baltimore, Maryland. One of the highlights of the collection is a group of five ivory figurines from Predynastic Times (pre 3500-3100 BCE) depicting a couple, a man with a child, and two females. Representations from other periods include ordinary as well as dwarf deities. The dwarf gods, Bes and Ptah, are frequently depicted holding or biting snakes or standing on crocodiles symbolizing their ability to ward off dangers. A couple of statuettes from the Greco-Roman Period that, in contrast to earlier Egyptian Periods, depict harsh physical anomalies, twisted bodies, and facial pain. The artistic impression can be interpreted as either tragic or humorous. The grotesque depiction of dwarfs during the Greco-Roman Period in ancient Egypt is believed to be due to a greater infusion of Hellenistic influence. This study provides a microcosm of the legacy of dwarfs in ancient Egypt and supports the premise that dwarfs were accepted and integrated in the ancient Egyptian society, and with a few exceptions, their disorder was not depicted as a physical handicap. Copyright © 2010 Wiley-Liss, Inc.

White dwarfs: connection with masses of the parent stars

International Nuclear Information System (INIS)

Amnuel', P.R.; Guseinov, O.Kh.; Novruzova, Kh.I.; Rustamov, Yu.S.

1988-01-01

A relationship between the mass of a white dwarf and the mass of the parent star on the main sequence is established. The white dwarf birth-rate matches the birth-rate (death-rate) of main sequence stars

White dwarf atmospheres and circumstellar environments

CERN Document Server

Hoard, Donald W

2012-01-01

Written by selected astronomers at the forefront of their fields, this timely and novel book compiles the latest results from research on white dwarf stars, complementing existing literature by focusing on fascinating new developments in our understanding of the atmospheric and circumstellar environments of these stellar remnants. Complete with a thorough refresher on the observational characteristics and physical basis for white dwarf classification, this is a must-have resource for researchers interested in the late stages of stellar evolution, circumstellar dust and nebulae, and the future

Stroemgren photometry of southern white dwarfs

International Nuclear Information System (INIS)

Bessell, M.S.; Wickramasinghe, D.T.

1978-01-01

Colours of southern white dwarfs in the uvby (Stroemgren four-colour) system have been obtained. The results are compared with those of Graham. The extensive absolute photometry of white dwarfs published by Greenstein has also been transferred into the four-colour system and both sets of results are compared with model atmosphere calculations. The scatter in log (g) is higher than previously supposed, and the evidence for an increase in at the cooler (Tsub(e) < 10 000 K) end of the DA sequence is discussed. (author)

Energy transport in radially accreting white dwarf stars

Energy Technology Data Exchange (ETDEWEB)

Thompson, A.M.

1986-10-01

Some of the non-thermal energy transport processes which may be present in a white dwarf accretion column are examined and it is determined whether these could in any way contribute to a resolution of the soft X-ray puzzle. The first two Chapters of this Thesis constitute a review of the observations and proposed models for white dwarf accretion columns. In Chapter 3 we show that in Kuijpers and Pringle's original bombardment model of white dwarf accretion columns, in which the energy of the accreting material is deposited uniformly into a static atmosphere which then radiates the energy away as optically thin bremsstrahlung/line radiation, an incorrect Coulomb collisional timescale was used. In Chapter 4 we extend the calculations of Chapter 3 to include the effect of cyclotron radiation. It is concluded that a cyclotron cooled bombardment solution for a white dwarf accretion column may exist. We extend this calculation to derive a simple piecewise uniform temperature structure for such an accretion column, incorporating the effect of thermal conduction. In Chaper 5 we examine two of the non thermal emission mechanisms that might be present in white dwarf accretion columns:- non thermal Lyman-{alpha} emission and non thermal inverse bremsstrahlung emission. It is shown that neither would actually be sufficiently large to be detectable. In Chapter 6 some possible extensions to the work presented are suggested. (author).

Fate of accreting white dwarfs: Type I supernovae vs collapse

International Nuclear Information System (INIS)

Nomoto, Ken'ichi.

1986-01-01

The final fate of accreting C + O white dwarfs is either thermonuclear explosion or collapse, if the white dwarf mass grows to the Chandrasekhar mass. We discuss how the fate depends on the initial mass, age, composition of the white dwarf and the mass accretion rate. Relatively fast accretion leads to a carbon deflagration at low central density that gives rise to a Type Ia supernova. Slower accretion induces a helium detonation that could be observed as a Type Ib supernova. If the initial mass of the C + O white dwarf is larger than 1.2 Msub solar, a carbon deflagration starts at high central density and induces a collapse of the white dwarf to form a neutron star. We examine the critical condition for which a carbon deflagration leads to collapse, not explosion. For the case of explosion, we discuss to what extent the nucleosynthesis models are consistent with spectra of Type Ia and Ib supernovae. 61 refs., 18 figs

Near-infrared imaging of white dwarfs with candidate debris disks

International Nuclear Information System (INIS)

Wang, Zhongxiang; Tziamtzis, Anestis; Wang, Xuebing

2014-01-01

We have carried out JHK s imaging of 12 white dwarf debris disk candidates from the WIRED Sloan Digital Sky Survey Data Release 7 catalog, aiming to confirm or rule out disks among these sources. On the basis of positional identification and the flux density spectra, we find that seven white dwarfs have excess infrared emission, but mostly at Wide-field Infrared Survey Explorer W1 and W2 bands. Four are due to nearby red objects consistent with background galaxies or very low mass dwarfs, and one exhibits excess emission at JHK s consistent with an unresolved L0 companion at the correct distance. While our photometry is not inconsistent with all seven excesses arising from disks, the stellar properties are distinct from the known population of debris disk white dwarfs, making the possibility questionable. In order to further investigate the nature of these infrared sources, warm Spitzer imaging is needed, which may help resolve galaxies from the white dwarfs and provide more accurate flux measurements.

Luminosities and temperatures of M dwarf stars from infrared photometry

Science.gov (United States)

Veeder, G. J.

1974-01-01

Bolometric magnitudes for a large number of M type dwarf stars, obtained by broadband infrared photometry at 1.65, 2.2, and 3.5 microns, are reviewed. The data obtained indicate that one parameter is sufficient to describe the blanketing in all of the UBVRI bands for all types of M dwarfs. In general, late M dwarfs seem to have lower effective temperatures than are predicted by theoretical models.

SURFACE BRIGHTNESS PROFILES OF DWARF GALAXIES. I. PROFILES AND STATISTICS

International Nuclear Information System (INIS)

Herrmann, Kimberly A.; Hunter, Deidre A.; Elmegreen, Bruce G.

2013-01-01

Radial surface brightness profiles of spiral galaxies are classified into three types: (I) single exponential, or the light falls off with one exponential to a break before falling off (II) more steeply, or (III) less steeply. Profile breaks are also found in dwarf disks, but some dwarf Type IIs are flat or increasing out to a break before falling off. Here we re-examine the stellar disk profiles of 141 dwarfs: 96 dwarf irregulars (dIms), 26 Blue Compact Dwarfs (BCDs), and 19 Magellanic-type spirals (Sms). We fit single, double, or even triple exponential profiles in up to 11 passbands: GALEX FUV and NUV, ground-based UBVJHK and Hα, and Spitzer 3.6 and 4.5 μm. We find that more luminous galaxies have brighter centers, larger inner and outer scale lengths, and breaks at larger radii; dwarf trends with M B extend to spirals. However, the V-band break surface brightness is independent of break type, M B , and Hubble type. Dwarf Type II and III profiles fall off similarly beyond the breaks but have different interiors and IIs break ∼twice as far as IIIs. Outer Type II and III scale lengths may have weak trends with wavelength, but pure Type II inner scale lengths clearly decrease from the FUV to visible bands whereas Type III inner scale lengths increase with redder bands. This suggests the influence of different star formation histories on profile type, but nonetheless the break location is approximately the same in all passbands. Dwarfs continue trends between profile and Hubble types such that later-type galaxies have more Type II but fewer Type I and III profiles than early-type spirals. BCDs and Sms are over-represented as Types III and II, respectively, compared to dIms

Gas, Stars, and Star Formation in Alfalfa Dwarf Galaxies

Science.gov (United States)

Huang, Shan; Haynes, Martha P.; Giovanelli, Riccardo; Brinchmann, Jarle; Stierwalt, Sabrina; Neff, Susan G.

2012-01-01

We examine the global properties of the stellar and Hi components of 229 low H i mass dwarf galaxies extracted from the ALFALFA survey, including a complete sample of 176 galaxies with H i masses ALFALFA dwarfs are faint and of low surface brightness; only 56% of those within the SDSS footprint have a counterpart in the SDSS spectroscopic survey. A large fraction of the dwarfs have high specific star formation rates (SSFRs), and estimates of their SFRs and M* obtained by SED fitting are systematically smaller than ones derived via standard formulae assuming a constant SFR. The increased dispersion of the SSFR distribution at M* approximately less than10(exp 8)M(sub 0) is driven by a set of dwarf galaxies that have low gas fractions and SSFRs; some of these are dE/dSphs in the Virgo Cluster. The imposition of an upper Hi mass limit yields the selection of a sample with lower gas fractions for their M* than found for the overall ALFALFA population. Many of the ALFALFA dwarfs, particularly the Virgo members, have H i depletion timescales shorter than a Hubble time. An examination of the dwarf galaxies within the full ALFALFA population in the context of global star formation (SF) laws is consistent with the general assumptions that gas-rich galaxies have lower SF efficiencies than do optically selected populations and that Hi disks are more extended than stellar ones.

Ageing in old degenerates: asteroseismology of white dwarf stars

International Nuclear Information System (INIS)

O'Donoghue, D.

1988-01-01

Recent results on the use of pulsations in white dwarf stars as seismic probes of their structure are reviewed. The evolution of stars to the white dwarf stage is first described, followed by a discussion of their structure as expected from the theory of stellar evolution. A summary of the salient points of stellar pulsation theory is given and then compared with observations of pulsating white dwarfs: the pulsations are non-radial 'g-mode' pulsations and occur in all white dwarfs as they cool through the temperature ranges defining each of the four 'instability strips' on the white dwarf cooling curve. The presence of only some of the possible pulsation modes in any given star suggest that a filter mechanism to select these modes is at work, possibly the chemical stratification of the star. The pulsation periods can be measured very accurately so that period changes, due to evolutionary cooling, can be detected over relatively short intervals (2 - 30 years). The detection of such period changes can be used to place interesting limits on the age of the Galaxy and ultimately the age of the Universe. 17 refs., 10 figs., 2 tabs

DISCOVERY OF AN UNUSUALLY RED L-TYPE BROWN DWARF

International Nuclear Information System (INIS)

Gizis, John E.; Castro, Philip J.; Faherty, Jacqueline K.; Liu, Michael C.; Aller, Kimberly M.; Shaw, John D.; Vrba, Frederick J.; Harris, Hugh C.; Deacon, Niall R.

2012-01-01

We report the discovery of an unusually red brown dwarf found in a search for high proper motion objects using WISE and 2MASS data. WISEP J004701.06+680352.1 is moving at 0.''44 yr –1 and lies relatively close to the Galactic plane (b = 5. 0 2). Near-infrared photometry and spectroscopy reveals that this is one of the reddest (2MASS J – K s 2.55 ± 0.08 mag) field L dwarfs yet detected, making this object an important member of the class of unusually red L dwarfs. We discuss evidence for thick condensate clouds and speculate on the age of the object. Although models by different research groups agree that thick clouds can explain the red spectrum, they predict dramatically different effective temperatures, ranging from 1100 K to 1600 K. This brown dwarf is well suited for additional studies of extremely dusty substellar atmospheres because it is relatively bright (K s = 13.05 ± 0.03 mag), which should also contribute to an improved understanding of young gas-giant planets and the transition between L and T brown dwarfs.

The unique structural parameters of the underlying host galaxies in blue compact dwarfs

International Nuclear Information System (INIS)

Janowiecki, Steven; Salzer, John J.

2014-01-01

The nature of possible evolutionary pathways between various types of dwarf galaxies is still not fully understood. Blue compact dwarf galaxies (BCDs) provide a unique window into dwarf galaxy formation and evolution and are often thought of as an evolutionary stage between different classes of dwarf galaxies. In this study we use deep optical and near-infrared observations of the underlying hosts of BCDs in order to study the structural differences between different types of dwarf galaxies. When compared with dwarf irregular galaxies of similar luminosities, we find that the underlying hosts of BCDs have significantly more concentrated light distributions, with smaller scale lengths and brighter central surface brightnesses. We demonstrate here that the underlying hosts of BCDs are distinct from the broad continuum of typical dwarf irregular galaxies, and that it is unlikely that most dwarf irregular galaxies can transform into a BCD or vice versa. Furthermore, we find that the starburst in a BCD only brightens it on average by ∼0.8 mag (factor of two), in agreement with other studies. It appears that a BCD is a long-lived and distinct type of dwarf galaxy that exhibits an exceptionally concentrated matter distribution. We suggest that it is this compact mass distribution that enables the strong star formation events that characterize this class of dwarf galaxy, that the compactness of the underlying host can be used as a distinguishing parameter between BCDs and other dwarf galaxies, and that it can also be used to identify BCDs which are not currently experiencing an intense starburst event.

AVOCADO: A Virtual Observatory Census to Address Dwarfs Origins

Science.gov (United States)

Sánchez-Janssen, Rubén; Sánchez-Janssen

2011-12-01

Dwarf galaxies are by far the most abundant of all galaxy types, yet their properties are still poorly understood-especially due to the observational challenge that their intrinsic faintness represents. AVOCADO aims at establishing firm conclusions on their formation and evolution by constructing a homogeneous, multiwavelength dataset for a statistically significant sample of several thousand nearby dwarfs (-18 < Mi < -14). Using public data and Virtual Observatory tools, we have built GALEX+SDSS+2MASS spectral energy distributions that are fitted by a library of single stellar population models. Star formation rates, stellar masses, ages and metallicities are further complemented with structural parameters that can be used to classify them morphologically. This unique dataset, coupled with a detailed characterization of each dwarf's environment, allows for a fully comprehensive investigation of their origins and to track the (potential) evolutionary paths between the different dwarf types.

WD0837+185: THE FORMATION AND EVOLUTION OF AN EXTREME MASS-RATIO WHITE-DWARF-BROWN-DWARF BINARY IN PRAESEPE

International Nuclear Information System (INIS)

Casewell, S. L.; Burleigh, M. R.; Wynn, G. A.; Alexander, R. D.; Lawrie, K. A.; Jameson, R. F.; Napiwotzki, R.; Dobbie, P. D.; Hodgkin, S. T.

2012-01-01

There is a striking and unexplained dearth of brown dwarf companions in close orbits ( ☉ (B9). The high mass of the white dwarf means the substellar companion must have been engulfed by the B star's envelope while it was on the late asymptotic giant branch (AGB). Hence, the initial separation of the system was ∼2 AU, with common envelope evolution reducing the separation to its current value. The initial and final orbital separations allow us to constrain the combination of the common envelope efficiency (α) and binding energy parameters (λ) for the AGB star to αλ ∼ 3. We examine the various formation scenarios and conclude that the substellar object was most likely captured by the white dwarf progenitor early in the life of the cluster, rather than forming in situ.

Feedback by Massive Black Holes in Gas-rich Dwarf Galaxies

Energy Technology Data Exchange (ETDEWEB)

Silk, Joseph [Institut d’Astrophysique, UMR 7095 CNRS, Université Pierre et Marie Curie, 98bis Blvd Arago, F-75014 Paris (France); AIM-Paris-Saclay, CEA/DSM/IRFU, CNRS, Univ Paris 7, F-91191, Gif-sur-Yvette (France); Department of Physics and Astronomy, The Johns Hopkins University, Homewood Campus, Baltimore, MD 21218 (United States); Beecroft Institute of Particle Astrophysics and Cosmology, Department of Physics, University of Oxford, Oxford OX1 3RH (United Kingdom)

2017-04-10

Could there be intermediate-mass black holes in essentially all old dwarf galaxies? I argue that current observations of active galactic nuclei in dwarfs allow such a radical hypothesis that provides early feedback during the epoch of galaxy formation and potentially provides a unifying explanation for many, if not all, of the dwarf galaxy anomalies, such as the abundance, core-cusp, “too-big-to-fail,” ultra-faint, and baryon-fraction issues. I describe the supporting arguments, which are largely circumstantial, and discuss a number of tests. There is no strong motivation for modifying the nature of cold dark matter in order to explain any of the dwarf galaxy “problems.”.

A Refined Search for Pulsations in White Dwarf Companions to Millisecond Pulsars

Science.gov (United States)

Kilic, Mukremin; Hermes, J. J.; Córsico, A. H.; Kosakowski, Alekzander; Brown, Warren R.; Antoniadis, John; Calcaferro, Leila M.; Gianninas, A.; Althaus, Leandro G.; Green, M. J.

2018-06-01

We present optical high-speed photometry of three millisecond pulsars with low-mass (<0.3 M⊙) white dwarf companions, bringing the total number of such systems with follow-up time-series photometry to five. We confirm the detection of pulsations in one system, the white dwarf companion to PSR J1738+0333, and show that the pulsation frequencies and amplitudes are variable over many months. A full asteroseismic analysis for this star is under-constrained, but the mode periods we observe are consistent with expectations for a M⋆ = 0.16 - 0.19M⊙ white dwarf, as suggested from spectroscopy. We also present the empirical boundaries of the instability strip for low-mass white dwarfs based on the full sample of white dwarfs, and discuss the distinction between pulsating low-mass white dwarfs and subdwarf A/F stars.

The K Dwarf Advantage for Biosignatures

Science.gov (United States)

Arney, Giada; Domagal-Goldman, Shawn David; Meadows, Victoria

2018-01-01

Biosignature detection is typically studied in the context of an atmosphere in chemical disequilibrium. Oxygen (O2) and methane (CH4) are generally considered the “canonical” biosignature disequilibrium pair. However, the modern CH4 concentration poses a major detection challenge to future direct imaging telescopes, and it has been difficult for Earth to accumulate spectrally detectable quantities of O2 and CH4 over its history (Olson et al 2016, Reinhard et al 2017). Even the lower atmospheric levels of O2 typical of the Earth’s Proterozoic eon (0.01-1% of the modern O2 amount) may have resulted in a reduced photochemical lifetime of CH4 due to decreased UV shielding of CH4 (Claire et al 2006, Goldblatt et al 2006). However, while the above is true for an Earthlike planet orbiting a sunlike star, the situation changes for other stars. For instance, Segura et al (2005) found longer photochemical lifetimes for CH4 in the atmospheres of Earthlike planets orbiting M dwarfs. M dwarfs, however, present several barriers to planetary habitability including desiccation during the stellar super-luminous pre-main sequence phase (Lugar and Barnes 2015) and tidal locking. K dwarfs, which comprise about 12% of all main sequence stars, avoid these M dwarf hazards, and will be important targets for future exoplanet direct imaging missions. Using a photochemical model, we find CH4 and O2 are simultaneously detectable in the atmospheres of K dwarf planets with various O2 concentrations ranging between Proterozoic levels and modern O2 amounts. For instance, for a planet with an Earth-like CH4 surface flux (1 x 1011 molecules/cm2/s) and a Proterozoic-like O2 level (1% of modern), the planet generates a CH4 surface mixing ratio of 1x10-5 for a planet orbiting the sun, and 1.5x10-4 – an order of magnitude more CH4 – for a planet orbiting a K6V star. This is enough to produce detectable CH4 and O2 for the planet orbiting the K6V star. We discuss the implications of this �

Spectroscopy of poorly known northern dwarf novae. Part. I

International Nuclear Information System (INIS)

Bruch, A.

1989-01-01

Spectroscopic observations of 12 dwarf novae are presented most of which hitherto unknown spectroscopically. The classifications as dwarf novae could be confirmed in most cases. Two objects remain doubtful: CI UMa and MR Per. The latter has the spectrum of a very late type main sequence star with hydrogen emissions and might be a flare star showing extremely slow flares, while the CI UMa spectrum does not contain any emission line above the noise level. In two dwarf novae - DX And and NS Per - absorption lines of the secondary star are newly detected

A visible and infrared study of the eclipsing dwarf nova OY Carinae

International Nuclear Information System (INIS)

Berriman, G.

1984-01-01

This paper presents four visible light curves of the highly inclined, short-period cataclysmic binary star OY Carinae in quiescence. These light curves show that the red dwarf eclipses both its white dwarf companion and the accretion disc and hotspot, which originate from material transferred from the red dwarf to the white dwarf. The consequences of the findings are discussed in the light of current ideas about the evolution of cataclysmic variable stars. (author)

New Y and T Dwarfs from WISE Identified by Methane Imaging

Science.gov (United States)

Tinney, C. G.; Kirkpatrick, J. Davy; Faherty, Jacqueline K.; Mace, Gregory N.; Cushing, Mike; Gelino, Christopher R.; Burgasser, Adam J.; Sheppard, Scott S.; Wright, Edward L.

2018-06-01

We identify new Y- and T-type brown dwarfs from the WISE All Sky data release using images obtained in filters that divide the traditional near-infrared H and J bands into two halves—specifically {CH}}4{{s}} and CH4l in the H and J2, and J3 in the J. This proves to be very effective at identifying cool brown dwarfs via the detection of their methane absorption, as well as providing preliminary classification using methane colors and WISE -to-near-infrared colors. New and updated calibrations between T/Y spectral types and {CH}}4{{s}}–CH4l J3–W2, and {CH}}4{{s}}–W2 colors are derived, producing classification estimates good to a few spectral sub-types. We present photometry for a large sample of T and Y dwarfs in these filters, together with spectroscopy for 23 new ultra-cool dwarfs—2 Y dwarfs and 21 T dwarfs. We identify a further 8 new cool brown dwarfs, which we have high confidence are T dwarfs based on their methane photometry. We find that, for objects observed on a 4 m class telescope at J-band magnitudes of ∼20 or brighter, {CH}}4{{s}}–CH4l is the more powerful color for detecting objects and then estimating spectral types. Due to the lower sky background in the J-band, the J3 and J2 bands are more useful for identifying fainter cool dwarfs at J ≳ 22. The J3–J2 color is poor at estimating spectral types. But fortunately, once J3–J2 confirms that an object is a cool dwarf, the J3–W2 color is very effective at estimating approximate spectral types.

ON THE EFFICIENCY OF THE TIDAL STIRRING MECHANISM FOR THE ORIGIN OF DWARF SPHEROIDALS: DEPENDENCE ON THE ORBITAL AND STRUCTURAL PARAMETERS OF THE PROGENITOR DISKY DWARFS

International Nuclear Information System (INIS)

Kazantzidis, Stelios; Lokas, Ewa L.; Callegari, Simone; Mayer, Lucio; Moustakas, Leonidas A.

2011-01-01

The tidal stirring model posits the formation of dwarf spheroidal galaxies (dSphs) via the tidal interactions between late-type, rotationally supported dwarfs and Milky-Way-sized host galaxies. Using a comprehensive set of collisionless N-body simulations, we investigate the efficiency of the tidal stirring mechanism for the origin of dSphs. In particular, we examine the degree to which the tidal field of the primary galaxy affects the sizes, masses, shapes, and kinematics of the disky dwarfs for a range of dwarf orbital and structural parameters. Our study is the first to employ self-consistent, equilibrium models for the progenitor dwarf galaxies constructed from a composite distribution function and consisting of exponential stellar disks embedded in massive, cosmologically motivated dark matter halos. Exploring a wide variety of dwarf orbital configurations and initial structures, we demonstrate that in the majority of cases the disky dwarfs experience significant mass loss and their stellar distributions undergo a dramatic morphological, as well as dynamical, transformation. Specifically, the stellar components evolve from disks to bars and finally to pressure-supported, spheroidal systems with kinematic and structural properties akin to those of the classic dSphs in the Local Group (LG) and similar environments. The self-consistency of the adopted dwarf models is crucial for confirming this complex transformation process via tidally induced dynamical instabilities and impulsive tidal heating of the stellar distribution. Our results suggest that such tidal transformations should be common occurrences within the currently favored cosmological paradigm and highlight the key factor responsible for an effective metamorphosis to be the strength of the tidal shocks at the pericenters of the orbit. We also demonstrate that the combination of short orbital times and small pericentric distances, characteristic of dwarfs being accreted by their hosts at high redshift

Testing the white dwarf mass-radius relationship with eclipsing binaries

Science.gov (United States)

Parsons, S. G.; Gänsicke, B. T.; Marsh, T. R.; Ashley, R. P.; Bours, M. C. P.; Breedt, E.; Burleigh, M. R.; Copperwheat, C. M.; Dhillon, V. S.; Green, M.; Hardy, L. K.; Hermes, J. J.; Irawati, P.; Kerry, P.; Littlefair, S. P.; McAllister, M. J.; Rattanasoon, S.; Rebassa-Mansergas, A.; Sahman, D. I.; Schreiber, M. R.

2017-10-01

We present high-precision, model-independent, mass and radius measurements for 16 white dwarfs in detached eclipsing binaries and combine these with previously published data to test the theoretical white dwarf mass-radius relationship. We reach a mean precision of 2.4 per cent in mass and 2.7 per cent in radius, with our best measurements reaching a precision of 0.3 per cent in mass and 0.5 per cent in radius. We find excellent agreement between the measured and predicted radii across a wide range of masses and temperatures. We also find the radii of all white dwarfs with masses less than 0.48 M⊙ to be fully consistent with helium core models, but they are on average 9 per cent larger than those of carbon-oxygen core models. In contrast, white dwarfs with masses larger than 0.52 M⊙ all have radii consistent with carbon-oxygen core models. Moreover, we find that all but one of the white dwarfs in our sample have radii consistent with possessing thick surface hydrogen envelopes (10-5 ≥ MH/MWD ≥ 10-4), implying that the surface hydrogen layers of these white dwarfs are not obviously affected by common envelope evolution.

The chemical evolution of white dwarf atmospheres: Diffusion and accretion

International Nuclear Information System (INIS)

Vauclair, G.; Vauclair, S.; Greenstein, J.L.

1979-01-01

A study of diffusion processes in white dwarfs is presented. We are especially interested in the estimate of the diffusion time scales for C, N, O, Mg, and Ca along the cooling sequence. The effect of the radiative acceleration is important in hot white dwarfs while in cooler ones the thermal diffusion dominates the gravitational settling. In hot white dwarfs, there should be an observable amount of CNO elements unless they have previously left the stars by a selective wind. Observational tests of this result are discussed. The diffusion time scales are always short compared to the evolutionary time scales. It is shown that in both hydrogen and helium envelopes, the convection zone, even at its maximum depth, is not able to bring back to the stellar surface the metals which have previously diffused downwards. The diffusion alone predicts a complete absence of metals in white dwarf atmospheres and envelopes. As metals are observed in white dwarfs, at least at effective temperatures lower than 15,000 K, there must be some mechanism competing with diffusion. We investigate the competition between diffusion and accretion and propose a general scheme for the chemical evolution of white dwarf atmospheres along the cooling sequence. (orig.)

The DB gap and a new class of pulsating white dwarfs