Runaway companions of supernova remnants with Gaia

Science.gov (United States)

Boubert, Douglas; Fraser, Morgan; Evans, N. Wyn

2018-04-01

It is expected that most massive stars have companions and thus that some core-collapse supernovae should have a runaway companion. The precise astrometry and photometry provided by Gaia allows for the systematic discovery of these runaway companions. We combine a prior on the properties of runaway stars from binary evolution with data from TGAS and APASS to search for runaway stars within ten nearby supernova remnants. We strongly confirm the existing candidate HD 37424 in S147, propose the Be star BD+50 3188 to be associated with HB 21, and suggest tentative candidates for the Cygnus and Monoceros Loops.

Search for white dwarf companions of cool stars with peculiar element abundances

Energy Technology Data Exchange (ETDEWEB)

Boehm-Vitense, E.

1984-01-01

A search for a white dwarf companions of cool stars with peculiar element abundances was undertaken. One additional star the xi Cet, was found with a white dwarf companion. It was found that HR 1016, 56Uma, 16 Ser, have high excitation emission lines which indicate a high temperature object in the system. It is suggested that since these indications for high temperature companions were seen for all nearby Ba stars, it is highly probable that all Ba stars have white dwarf companions, and that the peculiar element abundances seen in the Ba stars are due to mass transfer. Observations, arguments and conclusions are presented. White dwarf companions were not found. Together with the Li and Be abundances and the chromospheric emission line spectra in these stars were studied. No white dwarf companions were seen for subgiant CH stars.

Search for white dwarf companions of cool stars with peculiar element abundances

International Nuclear Information System (INIS)

Boehm-Vitense, E.

1984-01-01

A search for a white dwarf companions of cool stars with peculiar element abundances was undertaken. One additional star the xi Cet, was found with a white dwarf companion. It was found that HR 1016, 56Uma, 16 Ser, have high excitation emission lines which indicate a high temperature object in the system. It is suggested that since these indications for high temperature companions were seen for all nearby Ba stars, it is highly probable that all Ba stars have white dwarf companions, and that the peculiar element abundances seen in the Ba stars are due to mass transfer. Observations, arguments and conclusions are presented. White dwarf companions were not found. Together with the Li and Be abundances and the chromospheric emission line spectra in these stars were studied. No white dwarf companions were seen for subgiant CH stars

NEW BROWN DWARF COMPANIONS TO YOUNG STARS IN SCORPIUS-CENTAURUS

Energy Technology Data Exchange (ETDEWEB)

Janson, Markus [Department of Astrophysical Sciences, Princeton University, Princeton, NJ (United States); Jayawardhana, Ray; Bonavita, Mariangela [Department of Astronomy and Astrophysics, University of Toronto, Toronto, ON (Canada); Girard, Julien H. [European Southern Observatory, Santiago (Chile); Lafreniere, David [Department of Physics, University of Montreal, Montreal, QC (Canada); Gizis, John [Department of Physics and Astronomy, University of Delaware, Newark, DE (United States); Brandeker, Alexis, E-mail: janson@astro.princeton.edu [Department of Astronomy, Stockholm University, Stockholm (Sweden)

2012-10-10

We present the discoveries of three faint companions to young stars in the Scorpius-Centaurus region, imaged with the NICI instrument on Gemini South. We have confirmed all three companions through common proper motion tests. Follow-up spectroscopy has confirmed two of them, HIP 65423 B and HIP 65517 B, to be brown dwarfs, while the third, HIP 72099 B, is more likely a very low mass star just above the hydrogen burning limit. The detection of wide companions in the mass range of {approx}40-100 M{sub jup} complements previous work in the same region, reporting detections of similarly wide companions with lower masses, in the range of {approx}10-30 M{sub jup}. Such low masses near the deuterium burning limit have raised the question of whether those objects formed like planets or stars. The existence of intermediate objects as reported here could represent a bridge between lower-mass companions and stellar companions, but in any case demonstrate that mass alone may not provide a clear-cut distinction for the formation of low-mass companions to stars.

Searching For Low-mass Companions Of Cepheids

Science.gov (United States)

Remage Evans, Nancy; Bond, H.; Schaefer, G.; Karovska, M.; Mason, B.; DePasquale, J.; Pillitteri, I.; Guinan, E.; Engle, S.

2011-05-01

The role played by binary and multiple stars in star formation is receiving a great deal of attention, both theoretically and observationally. Two questions under discussion are how wide physical companions can be and how frequently massive stars have low mass companions. An important new observational tool is the development of high resolution imaging, both from space and from the ground (Adaptive Optics and interferometry). We are conducting a snapshot survey of the nearest Cepheids using the Hubble Space Telescope Wide Field Camera 3 (WFC3). The aim is to discover possible resolved low mass companions. Results from this survey will be discussed, including images of Eta Aql. X-ray luminosity can confirm or refute that putative low mass companions are young enough to be physical companions. This project tests the reality of both wide and low mass companions of these intermediate-mass stars.

On the absence of young white dwarf companions to five technetium stars

Science.gov (United States)

Smith, Verne V.; Lambert, David L.

1987-01-01

A search for hot companions to five stars of type MS and S has been carried out using the IUE satellite. No hot companions were detected for the MS stars HR 85, 4647, 6702, and 8062, and the S star HR 8714. Limits on the luminosities of possible white dwarf companions provide lower limits of 2-5x10 to the 8th yr to the ages of any degenerate companions. All five stars exhibit strong Tc I lines, and the presence of technetium, with a half-life of 2.1x10 to the 5th yr, signifies recent nucleosynthesis. The limits on the ages of possible white dwarf companions that are equal to or greater than 1000 half-lives of Tc exclude the possibility that the s-process elemental enhancement seen in these MS and S stars resulted from mass transfer from a more highly evolved companion (as is probably the mechanism by which barium stars are created). These MS and S stars represent a sample of true thermally pulsing asymptotic giant-branch stars.

A SUBSTELLAR COMPANION TO THE DUSTY PLEIADES STAR HD 23514

International Nuclear Information System (INIS)

Rodriguez, David R.; Zuckerman, B.; Marois, Christian; Macintosh, Bruce; Melis, Carl

2012-01-01

With adaptive optics imaging at Keck observatory, we have discovered a substellar companion to the F6 Pleiades star HD 23514, one of the dustiest main-sequence stars known to date (L IR /L * ∼ 2%). This is one of the first brown dwarfs discovered as a companion to a star in the Pleiades. The 0.06 M ☉ late-M secondary has a projected separation of ∼360 AU. The scarcity of substellar companions to stellar primaries in the Pleiades combined with the extremely dusty environment make this a unique system to study.

Wide cool and ultracool companions to nearby stars from Pan-STARRS 1

International Nuclear Information System (INIS)

Deacon, Niall R.; Liu, Michael C.; Magnier, Eugene A.; Aller, Kimberly M.; Best, William M. J.; Bowler, Brendan P.; Burgett, William S.; Chambers, Kenneth C.; Flewelling, H.; Kaiser, Nick; Kudritzki, Rolf-Peter; Morgan, Jeff S.; Tonry, John L.; Dupuy, Trent; Mann, Andrew W.; Redstone, Joshua A.; Draper, Peter W.; Metcalfe, Nigel; Hodapp, Klaus W.; Price, Paul A.

2014-01-01

We present the discovery of 57 wide (>5'') separation, low-mass (stellar and substellar) companions to stars in the solar neighborhood identified from Pan-STARRS 1 (PS1) data and the spectral classification of 31 previously known companions. Our companions represent a selective subsample of promising candidates and span a range in spectral type of K7-L9 with the addition of one DA white dwarf. These were identified primarily from a dedicated common proper motion search around nearby stars, along with a few as serendipitous discoveries from our Pan-STARRS 1 brown dwarf search. Our discoveries include 23 new L dwarf companions and one known L dwarf not previously identified as a companion. The primary stars around which we searched for companions come from a list of bright stars with well-measured parallaxes and large proper motions from the Hipparcos catalog (8583 stars, mostly A-K dwarfs) and fainter stars from other proper motion catalogs (79170 stars, mostly M dwarfs). We examine the likelihood that our companions are chance alignments between unrelated stars and conclude that this is unlikely for the majority of the objects that we have followed-up spectroscopically. We also examine the entire population of ultracool (>M7) dwarf companions and conclude that while some are loosely bound, most are unlikely to be disrupted over the course of ∼10 Gyr. Our search increases the number of ultracool M dwarf companions wider than 300 AU by 88% and increases the number of L dwarf companions in the same separation range by 82%. Finally, we resolve our new L dwarf companion to HIP 6407 into a tight (0.''13, 7.4 AU) L1+T3 binary, making the system a hierarchical triple. Our search for these key benchmarks against which brown dwarf and exoplanet atmosphere models are tested has yielded the largest number of discoveries to date.

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.

Ages of young star clusters, massive blue stragglers, and the upper mass limit of stars: Analyzing age-dependent stellar mass functions

Energy Technology Data Exchange (ETDEWEB)

Schneider, F. R. N.; Izzard, R. G.; Langer, N.; Stolte, A.; Hußmann, B. [Argelander-Institut für Astronomie der Universität Bonn, Auf dem Hügel 71, D-53121 Bonn (Germany); De Mink, S. E. [Observatories of the Carnegie Institution for Science, 813 Santa Barbara St, Pasadena, CA 91101 (United States); De Koter, A.; Sana, H. [Astronomical Institute " Anton Pannekoek" , Amsterdam University, Science Park 904, 1098 XH, Amsterdam (Netherlands); Gvaramadze, V. V. [Sternberg Astronomical Institute, Lomonosov Moscow State University, Universitetskij Pr. 13, Moscow 119992 (Russian Federation); Liermann, A., E-mail: fschneid@astro.uni-bonn.de [Max Planck Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany)

2014-01-10

Massive stars rapidly change their masses through strong stellar winds and mass transfer in binary systems. The latter aspect is important for populations of massive stars as more than 70% of all O stars are expected to interact with a binary companion during their lifetime. We show that such mass changes leave characteristic signatures in stellar mass functions of young star clusters that can be used to infer their ages and to identify products of binary evolution. We model the observed present-day mass functions of the young Galactic Arches and Quintuplet star clusters using our rapid binary evolution code. We find that the shaping of the mass function by stellar wind mass loss allows us to determine the cluster ages as 3.5 ± 0.7 Myr and 4.8 ± 1.1 Myr, respectively. Exploiting the effects of binary mass exchange on the cluster mass function, we find that the most massive stars in both clusters are rejuvenated products of binary mass transfer, i.e., the massive counterpart of classical blue straggler stars. This resolves the problem of an apparent age spread among the most luminous stars exceeding the expected duration of star formation in these clusters. We perform Monte Carlo simulations to probe stochastic sampling, which support the idea of the most massive stars being rejuvenated binary products. We find that the most massive star is expected to be a binary product after 1.0 ± 0.7 Myr in Arches and after 1.7 ± 1.0 Myr in Quintuplet. Today, the most massive 9 ± 3 stars in Arches and 8 ± 3 in Quintuplet are expected to be such objects. Our findings have strong implications for the stellar upper mass limit and solve the discrepancy between the claimed 150 M {sub ☉} limit and observations of four stars with initial masses of 165-320 M {sub ☉} in R136 and of supernova 2007bi, which is thought to be a pair-instability supernova from an initial 250 M {sub ☉} star. Using the stellar population of R136, we revise the upper mass limit to values in the range

Ages of young star clusters, massive blue stragglers, and the upper mass limit of stars: Analyzing age-dependent stellar mass functions

International Nuclear Information System (INIS)

Schneider, F. R. N.; Izzard, R. G.; Langer, N.; Stolte, A.; Hußmann, B.; De Mink, S. E.; Anton Pannekoek, Amsterdam University, Science Park 904, 1098 XH, Amsterdam (Netherlands))" data-affiliation=" (Astronomical Institute Anton Pannekoek, Amsterdam University, Science Park 904, 1098 XH, Amsterdam (Netherlands))" >De Koter, A.; Anton Pannekoek, Amsterdam University, Science Park 904, 1098 XH, Amsterdam (Netherlands))" data-affiliation=" (Astronomical Institute Anton Pannekoek, Amsterdam University, Science Park 904, 1098 XH, Amsterdam (Netherlands))" >Sana, H.; Gvaramadze, V. V.; Liermann, A.

2014-01-01

Massive stars rapidly change their masses through strong stellar winds and mass transfer in binary systems. The latter aspect is important for populations of massive stars as more than 70% of all O stars are expected to interact with a binary companion during their lifetime. We show that such mass changes leave characteristic signatures in stellar mass functions of young star clusters that can be used to infer their ages and to identify products of binary evolution. We model the observed present-day mass functions of the young Galactic Arches and Quintuplet star clusters using our rapid binary evolution code. We find that the shaping of the mass function by stellar wind mass loss allows us to determine the cluster ages as 3.5 ± 0.7 Myr and 4.8 ± 1.1 Myr, respectively. Exploiting the effects of binary mass exchange on the cluster mass function, we find that the most massive stars in both clusters are rejuvenated products of binary mass transfer, i.e., the massive counterpart of classical blue straggler stars. This resolves the problem of an apparent age spread among the most luminous stars exceeding the expected duration of star formation in these clusters. We perform Monte Carlo simulations to probe stochastic sampling, which support the idea of the most massive stars being rejuvenated binary products. We find that the most massive star is expected to be a binary product after 1.0 ± 0.7 Myr in Arches and after 1.7 ± 1.0 Myr in Quintuplet. Today, the most massive 9 ± 3 stars in Arches and 8 ± 3 in Quintuplet are expected to be such objects. Our findings have strong implications for the stellar upper mass limit and solve the discrepancy between the claimed 150 M ☉ limit and observations of four stars with initial masses of 165-320 M ☉ in R136 and of supernova 2007bi, which is thought to be a pair-instability supernova from an initial 250 M ☉ star. Using the stellar population of R136, we revise the upper mass limit to values in the range 200-500 M ☉ .

Ages of Young Star Clusters, Massive Blue Stragglers, and the Upper Mass Limit of Stars: Analyzing Age-dependent Stellar Mass Functions

Science.gov (United States)

Schneider, F. R. N.; Izzard, R. G.; de Mink, S. E.; Langer, N.; Stolte, A.; de Koter, A.; Gvaramadze, V. V.; Hußmann, B.; Liermann, A.; Sana, H.

2014-01-01

Massive stars rapidly change their masses through strong stellar winds and mass transfer in binary systems. The latter aspect is important for populations of massive stars as more than 70% of all O stars are expected to interact with a binary companion during their lifetime. We show that such mass changes leave characteristic signatures in stellar mass functions of young star clusters that can be used to infer their ages and to identify products of binary evolution. We model the observed present-day mass functions of the young Galactic Arches and Quintuplet star clusters using our rapid binary evolution code. We find that the shaping of the mass function by stellar wind mass loss allows us to determine the cluster ages as 3.5 ± 0.7 Myr and 4.8 ± 1.1 Myr, respectively. Exploiting the effects of binary mass exchange on the cluster mass function, we find that the most massive stars in both clusters are rejuvenated products of binary mass transfer, i.e., the massive counterpart of classical blue straggler stars. This resolves the problem of an apparent age spread among the most luminous stars exceeding the expected duration of star formation in these clusters. We perform Monte Carlo simulations to probe stochastic sampling, which support the idea of the most massive stars being rejuvenated binary products. We find that the most massive star is expected to be a binary product after 1.0 ± 0.7 Myr in Arches and after 1.7 ± 1.0 Myr in Quintuplet. Today, the most massive 9 ± 3 stars in Arches and 8 ± 3 in Quintuplet are expected to be such objects. Our findings have strong implications for the stellar upper mass limit and solve the discrepancy between the claimed 150 M ⊙ limit and observations of four stars with initial masses of 165-320 M ⊙ in R136 and of supernova 2007bi, which is thought to be a pair-instability supernova from an initial 250 M ⊙ star. Using the stellar population of R136, we revise the upper mass limit to values in the range 200-500 M ⊙.

Low-Mass Stars and Their Companions

Science.gov (United States)

Montet, Benjamin Tyler

In this thesis, I present seven studies aimed towards better understanding the demographics and physical properties of M dwarfs and their companions. These studies focus in turn on planetary, brown dwarf, and stellar companions to M dwarfs. I begin with an analysis of radial velocity and transit timing analyses of multi-transiting planetary systems, finding that if both signals are measured to sufficiently high precision the stellar and planetary masses can be measured to a high precision, eliminating a need for stellar models which may have systematic errors. I then combine long-term radial velocity monitoring and a direct imaging campaign to measure the occurrence rate of giant planets around M dwarfs. I find that 6.5 +/- 3.0% of M dwarfs host a Jupiter mass or larger planet within 20 AU, with a strong dependence on stellar metallicity. I then present two papers analyzing the LHS 6343 system, which contains a widely separated M dwarf binary (AB). Star A hosts a transiting brown dwarf (LHS 6343 C) with a 12.7 day period. By combining radial velocity data with transit photometry, I am able to measure the mass and radius of the brown dwarf to 2% precision, the most precise measurement of a brown dwarf to date. I then analyze four secondary eclipses of the LHS 6343 AC system as observed by Spitzer in order to measure the luminosity of the brown dwarf in both Spitzer bandpasses. I find the brown dwarf is consistent with theoretical models of an 1100 K T dwarf at an age of 5 Gyr and empirical observations of field T5-6 dwarfs with temperatures of 1070 +/- 130 K. This is the first non-inflated brown dwarf with a measured mass, radius, and multi-band photometry, making it an ideal test of evolutionary models of field brown dwarfs. Next, I present the results of an astrometric and radial velocity campaign to measure the orbit and masses of both stars in the GJ 3305 AB system, an M+M binary comoving with 51 Eridani, a more massive star with a directly imaged planetary

Massive stars in galaxies

International Nuclear Information System (INIS)

Humphreys, R.M.

1987-01-01

The relationship between the morphologic type of a galaxy and the evolution of its massive stars is explored, reviewing observational results for nearby galaxies. The data are presented in diagrams, and it is found that the massive-star populations of most Sc spiral galaxies and irregular galaxies are similar, while those of Sb spirals such as M 31 and M 81 may be affected by morphology (via differences in the initial mass function or star-formation rate). Consideration is also given to the stability-related upper luminosity limit in the H-R diagram of hypergiant stars (attributed to radiation pressure in hot stars and turbulence in cool stars) and the goals of future observation campaigns. 88 references

Hot subdwarf stars in close-up view. I. Rotational properties of subdwarf B stars in close binary systems and nature of their unseen companions

Science.gov (United States)

Geier, S.; Heber, U.; Podsiadlowski, Ph.; Edelmann, H.; Napiwotzki, R.; Kupfer, T.; Müller, S.

2010-09-01

The origin of hot subdwarf B stars (sdBs) is still unclear. About half of the known sdBs are in close binary systems for which common envelope ejection is the most likely formation channel. Little is known about this dynamic phase of binary evolution. Since most of the known sdB systems are single-lined spectroscopic binaries, it is difficult to derive masses and unravel the companions' nature, which is the aim of this paper. Due to the tidal influence of the companion in close binary systems, the rotation of the primary becomes synchronised to its orbital motion. In this case it is possible to constrain the mass of the companion, if the primary mass, its projected rotational velocity as well as its surface gravity are known. For the first time we measured the projected rotational velocities of a large sdB binary sample from high resolution spectra. We analysed a sample of 51 sdB stars in close binaries, 40 of which have known orbital parameters comprising half of all such systems known today. Synchronisation in sdB binaries is discussed both from the theoretical and the observational point of view. The masses and the nature of the unseen companions could be constrained in 31 cases. We found orbital synchronisation most likely to be established in binaries with orbital periods shorter than 1.2 d. Only in five cases it was impossible to decide whether the sdB's companion is a white dwarf or an M dwarf. The companions to seven sdBs could be clearly identified as late M stars. One binary may have a brown dwarf companion. The unseen companions of nine sdBs are white dwarfs with typical masses. The mass of one white dwarf companion is very low. In eight cases (including the well known system KPD1930+2752) the companion mass exceeds 0.9~M_⊙, four of which even exceed the Chandrasekhar limit indicating that they may be neutron stars. Even stellar mass black holes are possible for the most massive companions. The distribution of the inclinations of the systems with low

Search of massive star formation with COMICS

Science.gov (United States)

Okamoto, Yoshiko K.

2004-04-01

Mid-infrared observations is useful for studies of massive star formation. Especially COMICS offers powerful tools: imaging survey of the circumstellar structures of forming massive stars such as massive disks and cavity structures, mass estimate from spectroscopy of fine structure lines, and high dispersion spectroscopy to census gas motion around formed stars. COMICS will open the next generation infrared studies of massive star formation.

A dual-mask coronagraph for observing faint companions to binary stars

NARCIS (Netherlands)

Cady, E.; McElwain, M.; Kasdin, N.J.; Thalmann, C.

2011-01-01

Observations of binary stars for faint companions with conventional coronagraphic methods are challenging, as both targets will be bright enough to obscure any nearby faint companions if their scattered light is not suppressed. We propose coronagraphic examination of binary stars using an

A METAL-RICH LOW-GRAVITY COMPANION TO A MASSIVE MILLISECOND PULSAR

International Nuclear Information System (INIS)

Kaplan, D. L.; Bhalerao, V. B.; Van Kerkwijk, M. H.; Koester, D.; Kulkarni, S. R.; Stovall, K.

2013-01-01

Most millisecond pulsars with low-mass companions are in systems with either helium-core white dwarfs or non-degenerate (''black widow'' or ''redback'') stars. A candidate counterpart to PSR J1816+4510 was identified by Kaplan et al. whose properties were suggestive of both types of companions although identical to neither. We have assembled optical spectroscopy of the candidate companion and confirm that it is part of the binary system with a radial velocity amplitude of 343 ± 7 km s –1 , implying a high pulsar mass, M psr sin 3 i = 1.84 ± 0.11 M ☉ , and a companion mass M c sin 3 i = 0.193 ± 0.012 M ☉ , where i is the inclination of the orbit. The companion appears similar to proto-white dwarfs/sdB stars, with a gravity log 10 (g) = 4.9 ± 0.3, and effective temperature 16, 000 ± 500 K. The strongest lines in the spectrum are from hydrogen, but numerous lines from helium, calcium, silicon, and magnesium are present as well, with implied abundances of roughly 10 times solar (relative to hydrogen). As such, while from the spectrum the companion to PSR J1816+4510 is superficially most similar to a low-mass white dwarf, it has much lower gravity, is substantially larger, and shows substantial metals. Furthermore, it is able to produce ionized gas eclipses, which had previously been seen only for low-mass, non-degenerate companions in redback or black widow systems. We discuss the companion in relation to other sources, but find that we understand neither its nature nor its origins. Thus, the system is interesting for understanding unusual stellar products of binary evolution, as well as, independent of its nature, for determining neutron-star masses.

THE ROTATION RATES OF MASSIVE STARS: THE ROLE OF BINARY INTERACTION THROUGH TIDES, MASS TRANSFER, AND MERGERS

Energy Technology Data Exchange (ETDEWEB)

De Mink, S. E. [Space Telescope Science Institute, Baltimore, MD (United States); Langer, N.; Izzard, R. G. [Argelander-Institut fuer Astronomie der Universitaet Bonn, D-53121 Bonn (Germany); Sana, H.; De Koter, A. [Astronomical Institute Anton Pannekoek, University of Amsterdam, 1098 XH Amsterdam (Netherlands)

2013-02-20

Rotation is thought to be a major factor in the evolution of massive stars-especially at low metallicity-with consequences for their chemical yields, ionizing flux, and final fate. Deriving the birth spin distribution is of high priority given its importance as a constraint on theories of massive star formation and as input for models of stellar populations in the local universe and at high redshift. Recently, it has become clear that the majority of massive stars interact with a binary companion before they die. We investigate how this affects the distribution of rotation rates, through stellar winds, expansion, tides, mass transfer, and mergers. For this purpose, we simulate a massive binary-star population typical for our Galaxy assuming continuous star formation. We find that, because of binary interaction, 20{sup +5} {sub -10}% of all massive main-sequence stars have projected rotational velocities in excess of 200 km s{sup -1}. We evaluate the effect of uncertain input distributions and physical processes and conclude that the main uncertainties are the mass transfer efficiency and the possible effect of magnetic braking, especially if magnetic fields are generated or amplified during mass accretion and stellar mergers. The fraction of rapid rotators we derive is similar to that observed. If indeed mass transfer and mergers are the main cause for rapid rotation in massive stars, little room remains for rapidly rotating stars that are born single. This implies that spin-down during star formation is even more efficient than previously thought. In addition, this raises questions about the interpretation of the surface abundances of rapidly rotating stars as evidence for rotational mixing. Furthermore, our results allow for the possibility that all early-type Be stars result from binary interactions and suggest that evidence for rotation in explosions, such as long gamma-ray bursts, points to a binary origin.

Searching for Low-mass Companions of Cepheids, Part II

Science.gov (United States)

Remage Evans, Nancy; Tingle, E.; Bond, H. E.; Schaefer, G. H.; Mason, B.; Karovska, M.; Wolk, S.; Pillitteri, I.; DePasquale, J.; Guinan, E.; Engle, S.

2012-01-01

The formation of a binary/multiple system is an effective way to manipulate angular momentum during the star-formation process. The properties of binary systems (separations and mass ratios) are thus the ``fingerprints" of the process. Low mass companions are the most difficult to identify particularly for massive stars. We are conducting a snapshot survey of the nearest Cepheids (5 Msun stars) using the Hubble Space Telescope Wide Field Camera 3 (WFC3) to discover possible resolved low mass companions. The color-magnitude combination is the first approach to identifying probable physical companions. The distributions of mass and separation for these stars will be discussed. Financial suppoet was provided by Hubble grant GO-12215.01-A and the Chandra X-ray Center NASA contract NAS8-03060.

Evolution of the solar system in the presence of a solar companion star

International Nuclear Information System (INIS)

Hut, P.

1986-01-01

A review is presented of the dynamical implications of a companion star in a wide orbit around the sun, with a semimajor axis of about half a parsec. The motivation behind the hypothesis of a solar companion star is reviewed briefly along with alternative hypotheses, and the general problem of solar system dynamics with a solar companion star is discussed. Four principal questions are posed and answered concerning the consistency of the solar companion theory in providing the required modulation in comet arrival times: (1) What is the expected lifetime of a solar companion? (2) How stable is the orbital period? (3) Does a single perihelion passage of a solar companion perturb enough comets? (4) Do repeated perihelion passages of a solar companion perturb too many comets? Some applications outside the solar system involving wide binaries, interstellar clouds, and dark matter in the Galactic disk are discussed, and the viability of the solar companion theory is critically assessed

THE PREVALENCE AND IMPACT OF WOLF–RAYET STARS IN EMERGING MASSIVE STAR CLUSTERS

Energy Technology Data Exchange (ETDEWEB)

Sokal, Kimberly R.; Johnson, Kelsey E.; Indebetouw, Rémy [Department of Astronomy, University of Virginia, P.O. Box 3818, Charlottesville, VA 22903 (United States); Massey, Philip, E-mail: krs9tb@virginia.edu [Lowell Observatory, 1400 W Mars Hill Road, Flagstaff, AZ 86001 (United States)

2016-08-01

We investigate Wolf–Rayet (WR) stars as a source of feedback contributing to the removal of natal material in the early evolution of massive star clusters. Despite previous work suggesting that massive star clusters clear out their natal material before the massive stars evolve into the WR phase, WR stars have been detected in several emerging massive star clusters. These detections suggest that the timescale for clusters to emerge can be at least as long as the time required to produce WR stars (a few million years), and could also indicate that WR stars may be providing the tipping point in the combined feedback processes that drive a massive star cluster to emerge. We explore the potential overlap between the emerging phase and the WR phase with an observational survey to search for WR stars in emerging massive star clusters hosting WR stars. We select candidate emerging massive star clusters from known radio continuum sources with thermal emission and obtain optical spectra with the 4 m Mayall Telescope at Kitt Peak National Observatory and the 6.5 m MMT.{sup 4} We identify 21 sources with significantly detected WR signatures, which we term “emerging WR clusters.” WR features are detected in ∼50% of the radio-selected sample, and thus we find that WR stars are commonly present in currently emerging massive star clusters. The observed extinctions and ages suggest that clusters without WR detections remain embedded for longer periods of time, and may indicate that WR stars can aid, and therefore accelerate, the emergence process.

Exterior Companions to Hot Jupiters Orbiting Cool Stars Are Coplanar

Science.gov (United States)

Becker, Juliette C.; Vanderburg, Andrew; Adams, Fred C.; Khain, Tali; Bryan, Marta

2017-12-01

The existence of hot Jupiters has challenged theories of planetary formation since the first extrasolar planets were detected. Giant planets are generally believed to form far from their host stars, where volatile materials like water exist in their solid phase, making it easier for giant planet cores to accumulate. Several mechanisms have been proposed to explain how giant planets can migrate inward from their birth sites to short-period orbits. One such mechanism, called Kozai-Lidov migration, requires the presence of distant companions in orbits inclined by more than ˜40° with respect to the plane of the hot Jupiter’s orbit. The high occurrence rate of wide companions in hot-Jupiter systems lends support to this theory for migration. However, the exact orbital inclinations of these detected planetary and stellar companions is not known, so it is not clear whether the mutual inclination of these companions is large enough for the Kozai-Lidov process to operate. This paper shows that in systems orbiting cool stars with convective outer layers, the orbits of most wide planetary companions to hot Jupiters must be well aligned with the orbits of the hot Jupiters and the spins of the host stars. For a variety of possible distributions for the inclination of the companion, the width of the distribution must be less than ˜20° to recreate the observations with good fidelity. As a result, the companion orbits are likely well aligned with those of the hot Jupiters, and the Kozai-Lidov mechanism does not enforce migration in these systems.

MASSIVE STARS IN THE Cl 1813-178 CLUSTER: AN EPISODE OF MASSIVE STAR FORMATION IN THE W33 COMPLEX

International Nuclear Information System (INIS)

Messineo, Maria; Davies, Ben; Figer, Donald F.; Trombley, Christine; Kudritzki, R. P.; Valenti, Elena; Najarro, F.; Michael Rich, R.

2011-01-01

Young massive (M > 10 4 M sun ) stellar clusters are a good laboratory to study the evolution of massive stars. Only a dozen of such clusters are known in the Galaxy. Here, we report about a new young massive stellar cluster in the Milky Way. Near-infrared medium-resolution spectroscopy with UIST on the UKIRT telescope and NIRSPEC on the Keck telescope, and X-ray observations with the Chandra and XMM satellites, of the Cl 1813-178 cluster confirm a large number of massive stars. We detected 1 red supergiant, 2 Wolf-Rayet stars, 1 candidate luminous blue variable, 2 OIf, and 19 OB stars. Among the latter, twelve are likely supergiants, four giants, and the faintest three dwarf stars. We detected post-main-sequence stars with masses between 25 and 100 M sun . A population with age of 4-4.5 Myr and a mass of ∼10, 000 M sun can reproduce such a mixture of massive evolved stars. This massive stellar cluster is the first detection of a cluster in the W33 complex. Six supernova remnants and several other candidate clusters are found in the direction of the same complex.

Most sub-arcsecond companions of Kepler exoplanet candidate host stars are gravitationally bound

International Nuclear Information System (INIS)

Horch, Elliott P.; Howell, Steve B.; Everett, Mark E.; Ciardi, David R.

2014-01-01

Using the known detection limits for high-resolution imaging observations and the statistical properties of true binary and line-of-sight companions, we estimate the binary fraction of Kepler exoplanet host stars. Our speckle imaging programs at the WIYN 3.5 m and Gemini North 8.1 m telescopes have observed over 600 Kepler objects of interest and detected 49 stellar companions within ∼1 arcsec. Assuming binary stars follow a log-normal period distribution for an effective temperature range of 3000-10,000 K, then the model predicts that the vast majority of detected sub-arcsecond companions are long period (P > 50 yr), gravitationally bound companions. In comparing the model predictions to the number of real detections in both observational programs, we conclude that the overall binary fraction of host stars is similar to the 40%-50% rate observed for field stars.

Very massive runaway stars from three-body encounters

Science.gov (United States)

Gvaramadze, Vasilii V.; Gualandris, Alessia

2011-01-01

Very massive stars preferentially reside in the cores of their parent clusters and form binary or multiple systems. We study the role of tight very massive binaries in the origin of the field population of very massive stars. We performed numerical simulations of dynamical encounters between single (massive) stars and a very massive binary with parameters similar to those of the most massive known Galactic binaries, WR 20a and NGC 3603-A1. We found that these three-body encounters could be responsible for the origin of high peculiar velocities (≥70 km s-1) observed for some very massive (≥60-70 M⊙) runaway stars in the Milky Way and the Large Magellanic Cloud (e.g. λ Cep, BD+43°3654, Sk -67°22, BI 237, 30 Dor 016), which can hardly be explained within the framework of the binary-supernova scenario. The production of high-velocity massive stars via three-body encounters is accompanied by the recoil of the binary in the opposite direction to the ejected star. We show that the relative position of the very massive binary R145 and the runaway early B-type star Sk-69°206 on the sky is consistent with the possibility that both objects were ejected from the central cluster, R136, of the star-forming region 30 Doradus via the same dynamical event - a three-body encounter.

AN APPARENT PRECESSING HELICAL OUTFLOW FROM A MASSIVE EVOLVED STAR: EVIDENCE FOR BINARY INTERACTION

Energy Technology Data Exchange (ETDEWEB)

Lau, R. M.; Hankins, M. J.; Herter, T. L. [Astronomy Department, Cornell University, Ithaca, NY 14853-6801 (United States); Morris, M. R. [Department of Physics and Astronomy, University of California, Los Angeles, 430 Portola Plaza, Los Angeles, CA 90095 (United States); Mills, E. A. C. [National Radio Astronomy Observatory, P.O. Box O 1009, Lopezville Drive, Socorro, NM 87801 (United States); Ressler, M. E. [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States)

2016-02-20

Massive, evolved stars play a crucial role in the metal enrichment, dust budget, and energetics of the interstellar medium; however, the details of their evolution are uncertain because of their rarity and short lifetimes before exploding as supernovae. Discrepancies between theoretical predictions from single-star evolutionary models and observations of massive stars have evoked a shifting paradigm that implicates the importance of binary interaction. We present mid- to far-infrared observations from the Stratospheric Observatory for Infrared Astronomy of a conical “helix” of warm dust (∼180 K) that appears to extend from the Wolf–Rayet star WR102c. Our interpretation of the helix is a precessing, collimated outflow that emerged from WR102c during a previous evolutionary phase as a rapidly rotating luminous blue variable. We attribute the precession of WR102c to gravitational interactions with an unseen compact binary companion whose orbital period can be constrained to 800 days < P < 1400 days from the inferred precession period, τ{sub p} ∼ 1.4 × 10{sup 4} yr, and limits imposed on the stellar and orbital parameters of the system. Our results concur with the range of orbital periods (P ≲ 1500 days) where spin-up via mass exchange is expected to occur for massive binary systems.

OGLE-2008-BLG-355Lb: A massive planet around a late-type star

Energy Technology Data Exchange (ETDEWEB)

Koshimoto, N.; Sumi, T.; Fukagawa, M.; Shibai, H. [Department of Earth and Space Science, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043 (Japan); Udalski, A. [Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa (Poland); Bennett, D. P. [Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States); Bond, I. A.; Ling, C. H. [Institute of Information and Mathematical Sciences, Massey University, Private Bag 102-904, North Shore Mail Centre, Auckland (New Zealand); Rattenbury, N.; Botzler, C. S.; Freeman, M. [Department of Physics, University of Auckland, Private Bag 92019, Auckland (New Zealand); Abe, F.; Furusawa, K.; Itow, Y.; Masuda, K.; Matsubara, Y. [Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya, 464-8601 (Japan); Fukui, A. [Okayama Astrophysical Observatory, National Astronomical Observatory, 3037-5 Honjo, Kamogata, Asakuchi, Okayama 719-0232 (Japan); Muraki, Y. [Department of Physics, Konan University, Nishiokamoto 8-9-1, Kobe 658-8501 (Japan); Ohnishi, K. [Nagano National College of Technology, Nagano 381-8550 (Japan); Saito, To. [Tokyo Metropolitan College of Industrial Technology, Tokyo 116-8523 (Japan); Collaboration: MOA Collaboration; OGLE Collaboration; and others

2014-06-20

We report the discovery of a massive planet, OGLE-2008-BLG-355Lb. The light curve analysis indicates a planet:host mass ratio of q = 0.0118 ± 0.0006 at a separation of 0.877 ± 0.010 Einstein radii. We do not measure a significant microlensing parallax signal and do not have high angular resolution images that could detect the planetary host star. Therefore, we do not have a direct measurement of the host star mass. A Bayesian analysis, assuming that all host stars have equal probability to host a planet with the measured mass ratio, implies a host star mass of M{sub h}=0.37{sub −0.17}{sup +0.30} M{sub ⊙} and a companion of mass M{sub P}=4.6{sub −2.2}{sup +3.7}M{sub J}, at a projected separation of r{sub ⊥}=1.70{sub −0.30}{sup +0.29} AU. The implied distance to the planetary system is D {sub L} = 6.8 ± 1.1 kpc. A planetary system with the properties preferred by the Bayesian analysis may be a challenge to the core accretion model of planet formation, as the core accretion model predicts that massive planets are far more likely to form around more massive host stars. This core accretion model prediction is not consistent with our Bayesian prior of an equal probability of host stars of all masses to host a planet with the measured mass ratio. Thus, if the core accretion model prediction is right, we should expect that follow-up high angular resolution observations will detect a host star with a mass in the upper part of the range allowed by the Bayesian analysis. That is, the host would probably be a K or G dwarf.

The VLT-FLAMES survey of massive stars

NARCIS (Netherlands)

Evans, C.; Langer, N.; Brott, I.; Hunter, I.; Smartt, S.J.; Lennon, D.J.

2008-01-01

The VLT-FLAMES Survey of Massive Stars was an ESO Large Programme to understand rotational mixing and stellar mass loss in different metallicity environments, in order to better constrain massive star evolution. We gathered high-quality spectra of over 800 stars in the Galaxy and in the Magellanic

Limiting Accretion onto Massive Stars by Fragmentation-Induced Starvation

Energy Technology Data Exchange (ETDEWEB)

Peters, Thomas; /ZAH, Heidelberg; Klessen, Ralf S.; /ZAH, Heidelberg /KIPAC, Menlo Park; Mac Low, Mordecai-Mark; /Amer. Museum Natural Hist.; Banerjee, Robi; /ZAH, Heidelberg

2010-08-25

Massive stars influence their surroundings through radiation, winds, and supernova explosions far out of proportion to their small numbers. However, the physical processes that initiate and govern the birth of massive stars remain poorly understood. Two widely discussed models are monolithic collapse of molecular cloud cores and competitive accretion. To learn more about massive star formation, we perform simulations of the collapse of rotating, massive, cloud cores including radiative heating by both non-ionizing and ionizing radiation using the FLASH adaptive mesh refinement code. These simulations show fragmentation from gravitational instability in the enormously dense accretion flows required to build up massive stars. Secondary stars form rapidly in these flows and accrete mass that would have otherwise been consumed by the massive star in the center, in a process that we term fragmentation-induced starvation. This explains why massive stars are usually found as members of high-order stellar systems that themselves belong to large clusters containing stars of all masses. The radiative heating does not prevent fragmentation, but does lead to a higher Jeans mass, resulting in fewer and more massive stars than would form without the heating. This mechanism reproduces the observed relation between the total stellar mass in the cluster and the mass of the largest star. It predicts strong clumping and filamentary structure in the center of collapsing cores, as has recently been observed. We speculate that a similar mechanism will act during primordial star formation.

Limits on stellar companions to exoplanet host stars with eccentric planets

International Nuclear Information System (INIS)

Kane, Stephen R.; Hinkel, Natalie R.; Howell, Steve B.; Horch, Elliott P.; Feng, Ying; Wright, Jason T.; Ciardi, David R.; Everett, Mark E.; Howard, Andrew W.

2014-01-01

Though there are now many hundreds of confirmed exoplanets known, the binarity of exoplanet host stars is not well understood. This is particularly true of host stars that harbor a giant planet in a highly eccentric orbit since these are more likely to have had a dramatic dynamical history that transferred angular momentum to the planet. Here we present observations of four exoplanet host stars that utilize the excellent resolving power of the Differential Speckle Survey Instrument on the Gemini North telescope. Two of the stars are giants and two are dwarfs. Each star is host to a giant planet with an orbital eccentricity >0.5 and whose radial velocity (RV) data contain a trend in the residuals to the Keplerian orbit fit. These observations rule out stellar companions 4-8 mag fainter than the host star at passbands of 692 nm and 880 nm. The resolution and field of view of the instrument result in exclusion radii of 0.''05-1.''4, which excludes stellar companions within several AU of the host star in most cases. We further provide new RVs for the HD 4203 system that confirm that the linear trend previously observed in the residuals is due to an additional planet. These results place dynamical constraints on the source of the planet's eccentricities, place constraints on additional planetary companions, and inform the known distribution of multiplicity amongst exoplanet host stars.

Massive-Star Magnetospheres: Now in 3-D!

Science.gov (United States)

Townsend, Richard

Magnetic fields are unexpected in massive stars, due to the absence of a dynamo convection zone beneath their surface layers. Nevertheless, kilogauss-strength, ordered fields were detected in a small subset of these stars over three decades ago, and the intervening years have witnessed the steady expansion of this subset. A distinctive feature of magnetic massive stars is that they harbor magnetospheres --- circumstellar environments where the magnetic field interacts strongly with the star's radiation-driven wind, confining it and channelling it into energetic shocks. A wide range of observational signatures are associated with these magnetospheres, in diagnostics ranging from X-rays all the way through to radio emission. Moreover, these magnetospheres can play an important role in massive-star evolution, by amplifying angular momentum loss in the wind. Recent progress in understanding massive-star magnetospheres has largely been driven by magnetohydrodynamical (MHD) simulations. However, these have been restricted to two- dimensional axisymmetric configurations, with three-dimensional configurations possible only in certain special cases. These restrictions are limiting further progress; we therefore propose to develop completely general three-dimensional models for the magnetospheres of massive stars, on the one hand to understand their observational properties and exploit them as plasma-physics laboratories, and on the other to gain a comprehensive understanding of how they influence the evolution of their host star. For weak- and intermediate-field stars, the models will be based on 3-D MHD simulations using a modified version of the ZEUS-MP code. For strong-field stars, we will extend our existing Rigid Field Hydrodynamics (RFHD) code to handle completely arbitrary field topologies. To explore a putative 'photoionization-moderated mass loss' mechanism for massive-star magnetospheres, we will also further develop a photoionization code we have recently

Massive scalar counterpart of gravitational waves in scalarized neutron star binaries

Energy Technology Data Exchange (ETDEWEB)

Wang, Jing [Sun Yat-sen University, School of Physics and Astronomy, Guangzhou (China)

2017-09-15

In analogy with spontaneous magnetization of ferromagnets below the Curie temperature, a neutron star (NS), with a compactness above a certain critical value, may undergo spontaneous scalarization and exhibit an interior nontrivial scalar configuration. Consequently, the exterior spacetime is changed, and an external scalar field appears, which subsequently triggers a scalarization of its companion. The dynamical interplay produces a gravitational scalar counterpart of tensor gravitational waves. In this paper, we resort to scalar-tensor theory and demonstrate that the gravitational scalar counterpart from a double neutron star (DNS) and a neutron star-white dwarf (NS-WD) system become massive. We report that (1) a gravitational scalar background field, arising from convergence of external scalar fields, plays the role of gravitational scalar counterpart in scalarized DNS binary, and the appearance of a mass-dimensional constant in a Higgs-like gravitational scalar potential is responsible for a massive gravitational scalar counterpart with a mass of the order of the Planck scale; (2) a dipolar gravitational scalar radiated field, resulting from differing binding energies of NS and WD, plays the role of a gravitational scalar counterpart in scalarized orbital shrinking NS-WDs, which oscillates around a local and scalar-energy-density-dependent minimum of the gravitational scalar potential and obtains a mass of the order of about 10{sup -21} eV/c{sup 2}. (orig.)

Emission - line theoretical profiles for Wolf- Rayet stars with low-mass companions

International Nuclear Information System (INIS)

Antokhin, I.I.

1986-01-01

Profiles of the resonant line λ 765 A and the subordinate line λ 4058 of N4 have been calculated for a binary system medel consisting of the Wolf-Rayet star and the low-mass companion (possibly, a relativistic object) by means of Sobolev approximation. The equations of statistical equilibrium have been solved for the first 32 levels of N4. Two cases have been considered: 1) detached zone of N5 surrounding the Wolf-Rayet star and the companion; 2) common zone of N5. The criteria for detection of presence of a companion in line profile observations have been formulated

Supernovae from massive AGB stars

NARCIS (Netherlands)

Poelarends, A.J.T.; Izzard, R.G.; Herwig, F.; Langer, N.; Heger, A.

2006-01-01

We present new computations of the final fate of massive AGB-stars. These stars form ONeMg cores after a phase of carbon burning and are called Super AGB stars (SAGB). Detailed stellar evolutionary models until the thermally pulsing AGB were computed using three di erent stellar evolution codes. The

Massive stars and X-ray pulsars

International Nuclear Information System (INIS)

Henrichs, H.

1982-01-01

This thesis is a collection of 7 separate articles entitled: long term changes in ultraviolet lines in γ CAS, UV observations of γ CAS: intermittent mass-loss enhancement, episodic mass loss in γ CAS and in other early-type stars, spin-up and spin-down of accreting neutron stars, an excentric close binary model for the X Persei system, has a 97 minute periodicity in 4U 1700-37/HD 153919 really been discovered, and, mass loss and stellar wind in massive X-ray binaries. (Articles 1, 2, 5, 6 and 7 have been previously published). The first three articles are concerned with the irregular mass loss in massive stars. The fourth critically reviews thoughts since 1972 on the origin of the changes in periodicity shown by X-ray pulsars. The last articles indicate the relation between massive stars and X-ray pulsars. (C.F.)

KNOW THE STAR, KNOW THE PLANET. V. CHARACTERIZATION OF THE STELLAR COMPANION TO THE EXOPLANET HOST STAR HD 177830

Energy Technology Data Exchange (ETDEWEB)

Roberts, Lewis C. Jr.; Beichman, Charles; Burruss, Rick; Cady, Eric; Lockhart, Thomas G. [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena CA 91109 (United States); Oppenheimer, Rebecca; Brenner, Douglas; Luszcz-Cook, Statia; Nilsson, Ricky [American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024 (United States); Crepp, Justin R. [Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Baranec, Christoph [Institute for Astronomy, University of Hawai‘i at Mānoa, Hilo, HI 96720-2700 (United States); Dekany, Richard; Hillenbrand, Lynne [Division of Physics, Mathematics, and Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States); Hinkley, Sasha [School of Physics, University of Exeter, Stocker Road, Exeter, EX4 4QL (United Kingdom); King, David; Parry, Ian R. [Institute of Astronomy, University of Cambridge, Madingley Road., Cambridge, CB3 OHA (United Kingdom); Pueyo, Laurent [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Sivaramakrishnan, Anand; Soummer, Rémi [Department of Astronomy, Stockholm University, AlbaNova University Center, Roslagstullsbacken 21, SE-10691 Stockholm (Sweden); Rice, Emily L., E-mail: lewis.c.roberts@jpl.nasa.gov [Department of Engineering Science and Physics, College of Staten Island, City University of New York, Staten Island, NY 10314 (United States); and others

2015-10-15

HD 177830 is an evolved K0IV star with two known exoplanets. In addition to the planetary companions it has a late-type stellar companion discovered with adaptive optics imagery. We observed the binary star system with the PHARO near-IR camera and the Project 1640 coronagraph. Using the Project 1640 coronagraph and integral field spectrograph we extracted a spectrum of the stellar companion. This allowed us to determine that the spectral type of the stellar companion is a M4 ± 1 V. We used both instruments to measure the astrometry of the binary system. Combining these data with published data, we determined that the binary star has a likely period of approximately 800 years with a semimajor axis of 100–200 AU. This implies that the stellar companion has had little or no impact on the dynamics of the exoplanets. The astrometry of the system should continue to be monitored, but due to the slow nature of the system, observations can be made once every 5–10 years.

The Evolution of Low-Metallicity Massive Stars

Science.gov (United States)

Szécsi, Dorottya

2016-07-01

Massive star evolution taking place in astrophysical environments consisting almost entirely of hydrogen and helium - in other words, low-metallicity environments - is responsible for some of the most intriguing and energetic cosmic phenomena, including supernovae, gamma-ray bursts and gravitational waves. This thesis aims to investigate the life and death of metal-poor massive stars, using theoretical simulations of the stellar structure and evolution. Evolutionary models of rotating, massive stars (9-600 Msun) with an initial metal composition appropriate for the low-metallicity dwarf galaxy I Zwicky 18 are presented and analyzed. We find that the fast rotating models (300 km/s) become a particular type of objects predicted only at low-metallicity: the so-called Transparent Wind Ultraviolet INtense (TWUIN) stars. TWUIN stars are fast rotating massive stars that are extremely hot (90 kK), very bright and as compact as Wolf-Rayet stars. However, as opposed to Wolf-Rayet stars, their stellar winds are optically thin. As these hot objects emit intense UV radiation, we show that they can explain the unusually high number of ionizing photons of the dwarf galaxy I Zwicky 18, an observational quantity that cannot be understood solely based on the normal stellar population of this galaxy. On the other hand, we find that the most massive, slowly rotating models become another special type of object predicted only at low-metallicity: core-hydrogen-burning cool supergiant stars. Having a slow but strong stellar wind, these supergiants may be important contributors in the chemical evolution of young galactic globular clusters. In particular, we suggest that the low mass stars observed today could form in a dense, massive and cool shell around these, now dead, supergiants. This scenario is shown to explain the anomalous surface abundances observed in these low mass stars, since the shell itself, having been made of the mass ejected by the supergiant’s wind, contains nuclear

WHAT SETS THE INITIAL ROTATION RATES OF MASSIVE STARS?

International Nuclear Information System (INIS)

Rosen, Anna L.; Krumholz, Mark R.; Ramirez-Ruiz, Enrico

2012-01-01

The physical mechanisms that set the initial rotation rates in massive stars are a crucial unknown in current star formation theory. Observations of young, massive stars provide evidence that they form in a similar fashion to their low-mass counterparts. The magnetic coupling between a star and its accretion disk may be sufficient to spin down low-mass pre-main-sequence (PMS) stars to well below breakup at the end stage of their formation when the accretion rate is low. However, we show that these magnetic torques are insufficient to spin down massive PMS stars due to their short formation times and high accretion rates. We develop a model for the angular momentum evolution of stars over a wide range in mass, considering both magnetic and gravitational torques. We find that magnetic torques are unable to spin down either low-mass or high-mass stars during the main accretion phase, and that massive stars cannot be spun down significantly by magnetic torques during the end stage of their formation either. Spin-down occurs only if massive stars' disk lifetimes are substantially longer or their magnetic fields are much stronger than current observations suggest.

Nitrogen chronology of massive main sequence stars

NARCIS (Netherlands)

Köhler, K.; Borzyszkowski, M.; Brott, I.; Langer, N.; de Koter, A.

2012-01-01

Context. Rotational mixing in massive main sequence stars is predicted to monotonically increase their surface nitrogen abundance with time. Aims. We use this effect to design a method for constraining the age and the inclination angle of massive main sequence stars, given their observed luminosity,

Evolution of massive stars

International Nuclear Information System (INIS)

Loore, C. de

1984-01-01

The evolution of stars with masses larger than 15 sun masses is reviewed. These stars have large convective cores and lose a substantial fraction of their matter by stellar wind. The treatment of convection and the parameterisation of the stellar wind mass loss are analysed within the context of existing disagreements between theory and observation. The evolution of massive close binaries and the origin of Wolf-Rayet Stars and X-ray binaries is also sketched. (author)

Hyperfast pulsars as the remnants of massive stars ejected from young star clusters

Science.gov (United States)

Gvaramadze, Vasilii V.; Gualandris, Alessia; Portegies Zwart, Simon

2008-04-01

Recent proper motion and parallax measurements for the pulsar PSR B1508+55 indicate a transverse velocity of ~1100kms-1, which exceeds earlier measurements for any neutron star. The spin-down characteristics of PSR B1508+55 are typical for a non-recycled pulsar, which implies that the velocity of the pulsar cannot have originated from the second supernova disruption of a massive binary system. The high velocity of PSR B1508+55 can be accounted for by assuming that it received a kick at birth or that the neutron star was accelerated after its formation in the supernova explosion. We propose an explanation for the origin of hyperfast neutron stars based on the hypothesis that they could be the remnants of a symmetric supernova explosion of a high-velocity massive star which attained its peculiar velocity (similar to that of the pulsar) in the course of a strong dynamical three- or four-body encounter in the core of dense young star cluster. To check this hypothesis, we investigated three dynamical processes involving close encounters between: (i) two hard massive binaries, (ii) a hard binary and an intermediate-mass black hole (IMBH) and (iii) a single stars and a hard binary IMBH. We find that main-sequence O-type stars cannot be ejected from young massive star clusters with peculiar velocities high enough to explain the origin of hyperfast neutron stars, but lower mass main-sequence stars or the stripped helium cores of massive stars could be accelerated to hypervelocities. Our explanation for the origin of hyperfast pulsars requires a very dense stellar environment of the order of 106- 107starspc-3. Although such high densities may exist during the core collapse of young massive star clusters, we caution that they have never been observed.

Stars of type MS with evidence of white dwarf companions. [IUE, Main Sequence (MS)

Science.gov (United States)

Peery, Benjamin F., Jr.

1986-01-01

A search for white dwarf companions of MS-type stars was conducted, using IUE. The overendowments of these stars in typical S-process nuclides suggest that they, like the Ba II stars, may owe their peculiar compositions to earlier mass transfer. Short-wavelength IUE spectra show striking emission line variability in HD35155, HD61913, and 4 Ori; HD35155 and 4 Ori show evidence of white dwarf companions.

WIDE COMPANIONS TO HIPPARCOS STARS WITHIN 67 pc OF THE SUN

International Nuclear Information System (INIS)

Tokovinin, Andrei; Lépine, Sébastien

2012-01-01

A catalog of common-proper-motion (CPM) companions to stars within 67 pc of the Sun is constructed based on the SUPERBLINK proper-motion survey. It contains 1392 CPM pairs with angular separations 30'' –1 , and magnitudes and colors of the secondaries consistent with those of dwarfs in the (M V , V – J) diagram. In addition, we list 21 candidate white dwarf CPM companions with separations under 300'', about half of which should be physical. We estimate a 0.31 fraction of pairs with red dwarf companions to be physical systems (about 425 objects), while the rest (mostly wide pairs) are chance alignments. For each candidate companion, the probability of a physical association is evaluated. The distribution of projected separations s of the physical pairs between 2 kAU and 64 kAU follows f(s)∝s –1.5 , which decreases faster than Öpik's law. We find that solar-mass dwarfs have no less than 4.4% ± 0.3% companions with separations larger than 2 kAU, or 3.8% ± 0.3% per decade of orbital separation in the 2-16 kAU range. The distribution of mass ratio of those wide companions is approximately uniform in the 0.1 < q < 1.0 range, although we observe a dip at q ≅ 0.5 which, if confirmed, could be evidence of bimodal distribution of companion masses. New physical CPM companions to two exoplanet host stars are discovered.

Observations of Bright Massive Stars Using Small Size Telescopes

Science.gov (United States)

Beradze, Sopia; Kochiashvili, Nino

2017-11-01

The size of a telescope determines goals and objects of observations. During the latest decades it becomes more and more difficult to get photometric data of bright stars because most of telescopes of small sizes do not operate already. But there are rather interesting questions connected to the properties and evolution ties between different types of massive stars. Multi-wavelength photometric data are needed for solution of some of them. We are presenting our observational plans of bright Massive X-ray binaries, WR and LBV stars using a small size telescope. All these stars, which are presented in the poster are observational targets of Sopia Beradze's future PhD thesis. We already have got very interesting results on the reddening and possible future eruption of the massive hypergiant star P Cygni. Therefore, we decided to choose some additional interesting massive stars of different type for future observations. All Massive stars play an important role in the chemical evolution of galaxies because of they have very high mass loss - up to 10-4M⊙/a year. Our targets are on different evolutionary stages and three of them are the members of massive binaries. We plan to do UBVRI photometric observations of these stars using the 48 cm Cassegrain telescope of the Abastumani Astrophisical Observatory.

Massive stars and miniature robots: today's research and tomorrow's technologies

Science.gov (United States)

Taylor, William David

2013-03-01

This thesis documents the reduction of the VLT-FLAMES Tarantula Survey (VFTS) data set, whilst also describing the analysis for one of the serendipitous discoveries: the massive binary R139. This high-mass binary will provide an excellent future calibration point for stellar models, in part as it seems to defy certain expectations about its evolution. Out with the VFTS, a search for binary companions around a trio of B-type supergiants is presented. These stars are surrounded by nebulae that closely resemble the triple-ring structure associated with the poorly-understood SN1987A. Do these stars share a similar evolutionary fate? While strong evidence is found for periodic pulsations in one of the stars, there appears to be no indication of a short-period binary companion suggested in the literature. Gathering observations from a wide range of environments builds a fuller picture of massive stars, but the samples remain somewhat limited. The coming generation of extremely large telescopes will open new regions for studies like the VFTS. Fully utilising these remarkable telescopes will require many new technologies, and this thesis presents one such development project. For adaptive-optics corrected, multi-object instruments it will be necessary to position small pick-off mirrors in the telescope¿s focal plane to select the sub-fields on the sky. This could be most efficiently achieved if the mirrors were self-propelled, which has led to a miniature robot project called MAPS - the Micro Autonomous Positioning System. A number of robots have been built with a footprint of only 30 x 30mm. These wirelessly-controlled robots draw their power from the floor on which they operate and have shown the potential to be positioned to an accuracy of tens of microns. This thesis details much of the early design work and testing of the robots, and also the development of the camera imaging system used to determine the position of the robots. The MAPS project is ongoing and a

DISCOVERY OF A LOW-MASS COMPANION TO THE SOLAR-TYPE STAR TYC 2534-698-1

International Nuclear Information System (INIS)

Kane, Stephen R.; Mahadevan, Suvrath; Sivarani, Thirupathi; Cochran, William D.; Street, Rachel A.; Henry, Gregory W.; Williamson, Michael H.

2009-01-01

Brown dwarfs and low-mass stellar companions are interesting objects to study since they occupy the mass region between deuterium and hydrogen burning. We report here the serendipitous discovery of a low-mass companion in an eccentric orbit around a solar-type main-sequence star. The stellar primary, TYC 2534-698-1, is a G2V star that was monitored both spectroscopically and photometrically over the course of several months. Radial velocity observations indicate a minimum mass of 0.037 M sun and an orbital period of ∼103 days for the companion. Photometry outside of the transit window shows the star to be stable to within ∼6 millimags. The semimajor axis of the orbit places the companion in the 'brown dwarf desert' and we discuss potential follow-up observations that could constrain the mass of the companion.

Neutron stars structure in the context of massive gravity

Energy Technology Data Exchange (ETDEWEB)

Hendi, S.H.; Bordbar, G.H.; Panah, B. Eslam; Panahiyan, S., E-mail: hendi@shirazu.ac.ir, E-mail: ghbordbar@shirazu.ac.ir, E-mail: behzad.eslampanah@gmail.com, E-mail: sh.panahiyan@gmail.com [Physics Department and Biruni Observatory, College of Sciences, Shiraz University, Shiraz 71454 (Iran, Islamic Republic of)

2017-07-01

Motivated by the recent interests in spin−2 massive gravitons, we study the structure of neutron star in the context of massive gravity. The modifications of TOV equation in the presence of massive gravity are explored in 4 and higher dimensions. Next, by considering the modern equation of state for the neutron star matter (which is extracted by the lowest order constrained variational (LOCV) method with the AV18 potential), different physical properties of the neutron star (such as Le Chatelier's principle, stability and energy conditions) are investigated. It is shown that consideration of the massive gravity has specific contributions into the structure of neutron star and introduces new prescriptions for the massive astrophysical objects. The mass-radius relation is examined and the effects of massive gravity on the Schwarzschild radius, average density, compactness, gravitational redshift and dynamical stability are studied. Finally, a relation between mass and radius of neutron star versus the Planck mass is extracted.

Neutron stars structure in the context of massive gravity

Science.gov (United States)

Hendi, S. H.; Bordbar, G. H.; Eslam Panah, B.; Panahiyan, S.

2017-07-01

Motivated by the recent interests in spin-2 massive gravitons, we study the structure of neutron star in the context of massive gravity. The modifications of TOV equation in the presence of massive gravity are explored in 4 and higher dimensions. Next, by considering the modern equation of state for the neutron star matter (which is extracted by the lowest order constrained variational (LOCV) method with the AV18 potential), different physical properties of the neutron star (such as Le Chatelier's principle, stability and energy conditions) are investigated. It is shown that consideration of the massive gravity has specific contributions into the structure of neutron star and introduces new prescriptions for the massive astrophysical objects. The mass-radius relation is examined and the effects of massive gravity on the Schwarzschild radius, average density, compactness, gravitational redshift and dynamical stability are studied. Finally, a relation between mass and radius of neutron star versus the Planck mass is extracted.

Neutron stars structure in the context of massive gravity

International Nuclear Information System (INIS)

Hendi, S.H.; Bordbar, G.H.; Panah, B. Eslam; Panahiyan, S.

2017-01-01

Motivated by the recent interests in spin−2 massive gravitons, we study the structure of neutron star in the context of massive gravity. The modifications of TOV equation in the presence of massive gravity are explored in 4 and higher dimensions. Next, by considering the modern equation of state for the neutron star matter (which is extracted by the lowest order constrained variational (LOCV) method with the AV18 potential), different physical properties of the neutron star (such as Le Chatelier's principle, stability and energy conditions) are investigated. It is shown that consideration of the massive gravity has specific contributions into the structure of neutron star and introduces new prescriptions for the massive astrophysical objects. The mass-radius relation is examined and the effects of massive gravity on the Schwarzschild radius, average density, compactness, gravitational redshift and dynamical stability are studied. Finally, a relation between mass and radius of neutron star versus the Planck mass is extracted.

Do some x-ray stars have white dwarf companions

Science.gov (United States)

Mccollum, Bruce

1995-01-01

Some Be stars which are intermittent X-ray sources may have white dwarf companions rather than neutron stars. It is not possible to prove or rule out the existence of Be + WD systems using X-ray or optical data. However, the presence of a white dwarf could be established by the detection of its EUV continuum shortward of the Be star's continuum turnover at 100 A. Either the detection or the nondetection of Be + WD systems would have implications for models of Be star variability, models of Be binary system formation and evolution, and models of wind-fed accretion.

SALT Spectroscopy of Evolved Massive Stars

Science.gov (United States)

Kniazev, A. Y.; Gvaramadze, V. V.; Berdnikov, L. N.

2017-06-01

Long-slit spectroscopy with the Southern African Large Telescope (SALT) of central stars of mid-infrared nebulae detected with the Spitzer Space Telescope and Wide-Field Infrared Survey Explorer (WISE) led to the discovery of numerous candidate luminous blue variables (cLBVs) and other rare evolved massive stars. With the recent advent of the SALT fiber-fed high-resolution echelle spectrograph (HRS), a new perspective for the study of these interesting objects is appeared. Using the HRS we obtained spectra of a dozen newly identified massive stars. Some results on the recently identified cLBV Hen 3-729 are presented.

Massive stars in the Sagittarius Dwarf Irregular Galaxy

Science.gov (United States)

Garcia, Miriam

2018-02-01

Low metallicity massive stars hold the key to interpret numerous processes in the past Universe including re-ionization, starburst galaxies, high-redshift supernovae, and γ-ray bursts. The Sagittarius Dwarf Irregular Galaxy [SagDIG, 12+log(O/H) = 7.37] represents an important landmark in the quest for analogues accessible with 10-m class telescopes. This Letter presents low-resolution spectroscopy executed with the Gran Telescopio Canarias that confirms that SagDIG hosts massive stars. The observations unveiled three OBA-type stars and one red supergiant candidate. Pending confirmation from high-resolution follow-up studies, these could be the most metal-poor massive stars of the Local Group.

A Massive Star Census of the Starburst Cluster R136

Science.gov (United States)

Crowther, Paul

2012-10-01

We propose to carry out a comprehensive census of the most massive stars in the central parsec {4"} of the starburst cluster, R136, which powers the Tarantula Nebula in the LMC. R136 is both sufficiently massive that the upper mass function is richly populated and young enough that its most massive stars have yet to explode as supernovae. The identification of very massive stars in R136, up to 300 solar masses, raises general questions of star formation, binarity and feedback in young massive clusters. The proposed STIS spectral survey of 36 stars more massive than 50 solar masses within R136 is ground-breaking, of legacy value, and is specifically tailored to a} yield physical properties; b} detect the majority of binaries by splitting observations between Cycles 19 and 20; c} measure rotational velocities, relevant for predictions of rotational mixing; d} quantify mass-loss properties for very massive stars; e} determine surface compositions; f} measure radial velocities, relevant for runaway stars and cluster dynamics; g} quantify radiative and mechanical feedback. This census will enable the mass function of very massive stars to be measured for the first time, as a result of incomplete and inadequate spectroscopy to date. It will also perfectly complement our Tarantula Survey, a ground-based VLT Large Programme, by including the most massive stars that are inaccessible to ground-based visual spectroscopy due to severe crowding. These surveys, together with existing integrated UV and optical studies will enable 30 Doradus to serve as a bona-fide template for unresolved extragalactic starburst regions.

A Search for Pulsar Companions to OB Runaway Stars

Science.gov (United States)

Kaspi, V. M.

1995-01-01

We have searched for radio pulsar companions to 40 nearby OB runaway stars. Observations were made at 474 and 770 MHz with the NRAO 140 ft telescope. The survey was sensitive to long- period pulsars with flux densities of 1 mJy or more. One previously unknown pulsar was discovered, PSRJ2044+4614, while observing towards target O star BD+45,3260. Follow-up timing observations of the pulsar measured its position to high precision, revealing a 9' separation between the pulsar and the target star, unequivocally indicating they are not associated.

Evolution of massive close binary stars

International Nuclear Information System (INIS)

Masevich, A.G.; Tutukov, A.V.

1982-01-01

Some problems of the evolution of massive close binary stars are discussed. Most of them are nonevolutionized stars with close masses of components. After filling the Roche cavity and exchange of matter between the components the Wolf-Rayet star is formed. As a result of the supernovae explosion a neutron star or a black hole is formed in the system. The system does not disintegrate but obtains high space velocity owing to the loss of the supernovae envelope. The satellite of the neutron star or black hole - the star of the O or B spectral class loses about 10 -6 of the solar mass for a year. Around the neighbouring component a disc of this matter is formed the incidence of which on a compact star leads to X radiation appearance. The neutron star cannot absorb the whole matter of the widening component and the binary system submerges into the common envelope. As a result of the evolution of massive close binary systems single neutron stars can appear which after the lapse of some time become radiopulsars. Radiopulsars with such high space velocities have been found in our Galaxy [ru

THE RUNAWAY WHITE DWARF LP400-22 HAS A COMPANION

International Nuclear Information System (INIS)

Kilic, Mukremin; Brown, Warren R.; Kenyon, S. J.; Allende Prieto, Carlos; Swift, B.; Liebert, J.; Agueeros, M. A.

2009-01-01

We report the detection of a radial velocity companion to the extremely low-mass white dwarf (WD) LP400-22. The radial velocity of the WD shows variations with a semiamplitude of 119 km s -1 and a 0.98776 day period, which implies a companion mass of M ≥ 0.37 M sun . The optical photometry rules out a main-sequence companion. Thus the invisible companion is another WD or a neutron star. Using proper-motion measurements and the radial velocity of the binary system, we find that it has an unusual Galactic orbit. LP400-22 is moving away from the Galactic center with a velocity of 396 ± 43 km s -1 , which is very difficult to explain by supernova runaway ejection mechanisms. Dynamical interactions with a massive black hole like that in the Galactic center can in principle explain its peculiar velocity, if the progenitor was a triple star system comprised of a close binary and a distant tertiary companion. Until better proper motions become available, we consider LP400-22 to be most likely a halo star with a very unusual orbit.

WIDE COMPANIONS TO HIPPARCOS STARS WITHIN 67 pc OF THE SUN

Energy Technology Data Exchange (ETDEWEB)

Tokovinin, Andrei [Cerro Tololo Inter-American Observatory, Casilla 603, La Serena (Chile); Lepine, Sebastien, E-mail: atokovinin@ctio.noao.edu, E-mail: lepine@amnh.org [Department of Astrophysics, Division of Physical Sciences, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024 (United States)

2012-10-01

A catalog of common-proper-motion (CPM) companions to stars within 67 pc of the Sun is constructed based on the SUPERBLINK proper-motion survey. It contains 1392 CPM pairs with angular separations 30'' < {rho} < 1800'', relative proper motion between the two components less than 25 mas yr{sup -1}, and magnitudes and colors of the secondaries consistent with those of dwarfs in the (M{sub V} , V - J) diagram. In addition, we list 21 candidate white dwarf CPM companions with separations under 300'', about half of which should be physical. We estimate a 0.31 fraction of pairs with red dwarf companions to be physical systems (about 425 objects), while the rest (mostly wide pairs) are chance alignments. For each candidate companion, the probability of a physical association is evaluated. The distribution of projected separations s of the physical pairs between 2 kAU and 64 kAU follows f(s){proportional_to}s {sup -1.5}, which decreases faster than Oepik's law. We find that solar-mass dwarfs have no less than 4.4% {+-} 0.3% companions with separations larger than 2 kAU, or 3.8% {+-} 0.3% per decade of orbital separation in the 2-16 kAU range. The distribution of mass ratio of those wide companions is approximately uniform in the 0.1 < q < 1.0 range, although we observe a dip at q {approx_equal} 0.5 which, if confirmed, could be evidence of bimodal distribution of companion masses. New physical CPM companions to two exoplanet host stars are discovered.

Search for Black-Holes: the nature of the Unseen Companions of the Systems HD 152667 and 72754

International Nuclear Information System (INIS)

Freitas Pacheco, J.A. de

1978-01-01

The nature of the unseen companions in the single spectroscopic binary systems HD 152667 and HD 72754 is analysed. In the first system, the secondary is likely to be a normal B4 main sequence star while in HD 72754, the secondary, in spite of being the more massive star, is not detected. We cannot at the present, disregard the possibility that this massive object be associated with a collapsed star - a black-hole [pt

DISCOVERY OF THE COLDEST IMAGED COMPANION OF A SUN-LIKE STAR

International Nuclear Information System (INIS)

Thalmann, C.; Carson, J.; Goto, M.; Feldt, M.; Henning, T.; Klahr, H.; Mordasini, C.; Janson, M.; McElwain, M.; Egner, S.; Hayano, Y.; Suzuki, R.; Hashimoto, J.; Kandori, R.; Kudo, T.; Kusakabe, N.; Morino, J.-I.; Suto, H.; Tamura, M.; Hodapp, K. W.

2009-01-01

We present the discovery of a brown dwarf or possible planet at a projected separation of 1.''9 = 29 AU around the star GJ 758, placing it between the separations at which substellar companions are expected to form by core accretion (∼5 AU) or direct gravitational collapse (typically ∼>100 AU). The object was detected by direct imaging of its thermal glow with Subaru/HiCIAO. At 10-40 times the mass of Jupiter and a temperature of 550-640 K, GJ 758 B constitutes one of the few known T-type companions, and the coldest ever to be imaged in thermal light around a Sun-like star. Its orbit is likely eccentric and of a size comparable to Pluto's orbit, possibly as a result of gravitational scattering or outward migration. A candidate second companion is detected at 1.''2 at one epoch.

Revealing evolved massive stars with Spitzer

Science.gov (United States)

Gvaramadze, V. V.; Kniazev, A. Y.; Fabrika, S.

2010-06-01

Massive evolved stars lose a large fraction of their mass via copious stellar wind or instant outbursts. During certain evolutionary phases, they can be identified by the presence of their circumstellar nebulae. In this paper, we present the results of a search for compact nebulae (reminiscent of circumstellar nebulae around evolved massive stars) using archival 24-μm data obtained with the Multiband Imaging Photometer for Spitzer. We have discovered 115 nebulae, most of which bear a striking resemblance to the circumstellar nebulae associated with luminous blue variables (LBVs) and late WN-type (WNL) Wolf-Rayet (WR) stars in the Milky Way and the Large Magellanic Cloud (LMC). We interpret this similarity as an indication that the central stars of detected nebulae are either LBVs or related evolved massive stars. Our interpretation is supported by follow-up spectroscopy of two dozen of these central stars, most of which turn out to be either candidate LBVs (cLBVs), blue supergiants or WNL stars. We expect that the forthcoming spectroscopy of the remaining objects from our list, accompanied by the spectrophotometric monitoring of the already discovered cLBVs, will further increase the known population of Galactic LBVs. This, in turn, will have profound consequences for better understanding the LBV phenomenon and its role in the transition between hydrogen-burning O stars and helium-burning WR stars. We also report on the detection of an arc-like structure attached to the cLBV HD 326823 and an arc associated with the LBV R99 (HD 269445) in the LMC. Partially based on observations collected at the German-Spanish Astronomical Centre, Calar Alto, jointly operated by the Max-Planck-Institut für Astronomie Heidelberg and the Instituto de Astrofísica de Andalucía (CSIC). E-mail: vgvaram@mx.iki.rssi.ru (VVG); akniazev@saao.ac.za (AYK); fabrika@sao.ru (SF)

How Massive Single Stars End Their Life

Science.gov (United States)

Heger, A.; Fryer, C. L.; Woosley, S. E.; Langer, N.; Hartmann, D. H.

2003-01-01

How massive stars die-what sort of explosion and remnant each produces-depends chiefly on the masses of their helium cores and hydrogen envelopes at death. For single stars, stellar winds are the only means of mass loss, and these are a function of the metallicity of the star. We discuss how metallicity, and a simplified prescription for its effect on mass loss, affects the evolution and final fate of massive stars. We map, as a function of mass and metallicity, where black holes and neutron stars are likely to form and where different types of supernovae are produced. Integrating over an initial mass function, we derive the relative populations as a function of metallicity. Provided that single stars rotate rapidly enough at death, we speculate on stellar populations that might produce gamma-ray bursts and jet-driven supernovae.

MASSIVE INFANT STARS ROCK THEIR CRADLE

Science.gov (United States)

2002-01-01

Extremely intense radiation from newly born, ultra-bright stars has blown a glowing spherical bubble in the nebula N83B, also known as NGC 1748. A new NASA Hubble Space Telescope image has helped to decipher the complex interplay of gas and radiation of a star-forming region in a nearby galaxy. The image graphically illustrates just how these massive stars sculpt their environment by generating powerful winds that alter the shape of the parent gaseous nebula. These processes are also seen in our Milky Way in regions like the Orion Nebula. The Hubble telescope is famous for its contribution to our knowledge about star formation in very distant galaxies. Although most of the stars in the Universe were born several billions of years ago, when the Universe was young, star formation still continues today. This new Hubble image shows a very compact star-forming region in a small part of one of our neighboring galaxies - the Large Magellanic Cloud. This galaxy lies only 165,000 light-years from our Milky Way and can easily be seen with the naked eye from the Southern Hemisphere. Young, massive, ultra-bright stars are seen here just as they are born and emerge from the shelter of their pre-natal molecular cloud. Catching these hefty stars at their birthplace is not as easy as it may seem. Their high mass means that the young stars evolve very rapidly and are hard to find at this critical stage. Furthermore, they spend a good fraction of their youth hidden from view, shrouded by large quantities of dust in a molecular cloud. The only chance is to observe them just as they start to emerge from their cocoon - and then only with very high-resolution telescopes. Astronomers from France, the U.S., and Germany have used Hubble to study the fascinating interplay between gas, dust, and radiation from the newly born stars in this nebula. Its peculiar and turbulent structure has been revealed for the first time. This high-resolution study has also uncovered several individual stars

SUBSTELLAR-MASS COMPANIONS TO THE K-GIANTS HD 240237, BD +48 738, AND HD 96127

International Nuclear Information System (INIS)

Gettel, S.; Wolszczan, A.; Niedzielski, A.; Nowak, G.; Adamów, M.; Zieliński, P.; Maciejewski, G.

2012-01-01

We present the discovery of substellar-mass companions to three giant stars by the ongoing Penn State-Toruń Planet Search conducted with the 9.2 m Hobby-Eberly Telescope. The most massive of the three stars, K2-giant HD 240237, has a 5.3 M J minimum mass companion orbiting the star at a 746 day period. The K0-giant BD +48 738 is orbited by a ≥0.91 M J planet which has a period of 393 days and shows a nonlinear, long-term radial velocity (RV) trend that indicates a presence of another, more distant companion, which may have a substellar mass or be a low-mass star. The K2-giant HD 96127 has a ≥4.0 M J mass companion in a 647 day orbit around the star. The two K2-giants exhibit a significant RV noise that complicates the detection of low-amplitude, periodic variations in the data. If the noise component of the observed RV variations is due to solar-type oscillations, we show, using all the published data for the substellar companions to giants, that its amplitude is anti-correlated with stellar metallicity.

How massive the Wolf-Rayet stars are

International Nuclear Information System (INIS)

Niemela, V.S.

1981-01-01

If the Wolf-Rayet stars are produced by the evolution of massive stars with mass loss (Paczynski 1967, Conti 1976) from O stars to WN stars and thereafter to WC stars, then we may expect to observe a correlation of decreasing mean masses in the same sense as the evolution. Information about the masses of WR stars are obtained from studies of binary systems with WR components. (Auth.)

Toward Complete Statistics of Massive Binary Stars: Penultimate Results from the Cygnus OB2 Radial Velocity Survey

OpenAIRE

Kobulnicky, Henry A.; Kiminki, Daniel C.; Lundquist, Michael J.; Burke, Jamison; Chapman, James; Keller, Erica; Lester, Kathryn; Rolen, Emily K.; Topel, Eric; Bhattacharjee, Anirban; Smullen, Rachel A.; Alvarez, Carlos A. Vargas; Runnoe, Jessie C.; Dale, Daniel A.; Brotherton, Michael M.

2014-01-01

We analyze orbital solutions for 48 massive multiple-star systems in the Cygnus OB2 Association, 23 of which are newly presented here, to find that the observed distribution of orbital periods is approximately uniform in log P for P 45 d, even after correction for completeness, indicating either a lower binary fraction or a shift toward low-mass companions. A high degree of similarity (91% likelihood) between the Cyg OB2 period distribution and that of other surveys suggests that the binary p...

Detection of a white dwarf companion to the Hyades stars HD 27483

Science.gov (United States)

Boehm-Vitense, Erika

1993-01-01

We observed with IUE a white dwarf (WD) companion to the Hyades F6 V binary stars HD 27483. This system is known to be a close binary of two nearly equal stars with an orbital period of 3.05 days. Our IUE observations revealed the presence of a third star, a white dwarf with an effective temperature of 23,000 +/- 1000 K and a mass of approximately 0.6 solar mass. Its presence in the Hyades cluster with a known age permits me to derive the mass of its progenitor, which must have been about 2.3 solar masses. The presence of the white dwarf in a binary system opens the possibility that some of the envelope material, which was expelled by the WD progenitor, may have been collected by the F6 stars. We may thus be able to study abundance anomalies of the WD progenitor with known mass on the surface of the F6 companions.

The Final Stages of Massive Star Evolution and Their Supernovae

Science.gov (United States)

Heger, Alexander

In this chapter I discuss the final stages in the evolution of massive stars - stars that are massive enough to burn nuclear fuel all the way to iron group elements in their core. The core eventually collapses to form a neutron star or a black hole when electron captures and photo-disintegration reduce the pressure support to an extent that it no longer can hold up against gravity. The late burning stages of massive stars are a rich subject by themselves, and in them many of the heavy elements in the universe are first generated. The late evolution of massive stars strongly depends on their mass, and hence can be significantly effected by mass loss due to stellar winds and episodic mass loss events - a critical ingredient that we do not know as well as we would like. If the star loses all the hydrogen envelope, a Type I supernova results, if it does not, a Type II supernova is observed. Whether the star makes neutron star or a black hole, or a neutron star at first and a black hole later, and how fast they spin largely affects the energetics and asymmetry of the observed supernova explosion. Beyond photon-based astronomy, other than the sun, a supernova (SN 1987) has been the only object in the sky we ever observed in neutrinos, and supernovae may also be the first thing we will ever see in gravitational wave detectors like LIGO. I conclude this chapter reviewing the deaths of the most massive stars and of Population III stars.

Weighing the Smallest Stars

Science.gov (United States)

2005-01-01

VLT Finds Young, Very Low Mass Objects Are Twice As Heavy As Predicted Summary Thanks to the powerful new high-contrast camera installed at the Very Large Telescope, photos have been obtained of a low-mass companion very close to a star. This has allowed astronomers to measure directly the mass of a young, very low mass object for the first time. The object, more than 100 times fainter than its host star, is still 93 times as massive as Jupiter. And it appears to be almost twice as heavy as theory predicts it to be. This discovery therefore suggests that, due to errors in the models, astronomers may have overestimated the number of young "brown dwarfs" and "free floating" extrasolar planets. PR Photo 03/05: Near-infrared image of AB Doradus A and its companion (NACO SDI/VLT) A winning combination A star can be characterised by many parameters. But one is of uttermost importance: its mass. It is the mass of a star that will decide its fate. It is thus no surprise that astronomers are keen to obtain a precise measure of this parameter. This is however not an easy task, especially for the least massive ones, those at the border between stars and brown dwarf objects. Brown dwarfs, or "failed stars", are objects which are up to 75 times more massive than Jupiter, too small for major nuclear fusion processes to have ignited in its interior. To determine the mass of a star, astronomers generally look at the motion of stars in a binary system. And then apply the same method that allows determining the mass of the Earth, knowing the distance of the Moon and the time it takes for its satellite to complete one full orbit (the so-called "Kepler's Third Law"). In the same way, they have also measured the mass of the Sun by knowing the Earth-Sun distance and the time - one year - it takes our planet to make a tour around the Sun. The problem with low-mass objects is that they are very faint and will often be hidden in the glare of the brighter star they orbit, also when viewed

Black-hole-regulated star formation in massive galaxies

Science.gov (United States)

Martín-Navarro, Ignacio; Brodie, Jean P.; Romanowsky, Aaron J.; Ruiz-Lara, Tomás; van de Ven, Glenn

2018-01-01

Supermassive black holes, with masses more than a million times that of the Sun, seem to inhabit the centres of all massive galaxies. Cosmologically motivated theories of galaxy formation require feedback from these supermassive black holes to regulate star formation. In the absence of such feedback, state-of-the-art numerical simulations fail to reproduce the number density and properties of massive galaxies in the local Universe. There is, however, no observational evidence of this strongly coupled coevolution between supermassive black holes and star formation, impeding our understanding of baryonic processes within galaxies. Here we report that the star formation histories of nearby massive galaxies, as measured from their integrated optical spectra, depend on the mass of the central supermassive black hole. Our results indicate that the black-hole mass scales with the gas cooling rate in the early Universe. The subsequent quenching of star formation takes place earlier and more efficiently in galaxies that host higher-mass central black holes. The observed relation between black-hole mass and star formation efficiency applies to all generations of stars formed throughout the life of a galaxy, revealing a continuous interplay between black-hole activity and baryon cooling.

Black-hole-regulated star formation in massive galaxies.

Science.gov (United States)

Martín-Navarro, Ignacio; Brodie, Jean P; Romanowsky, Aaron J; Ruiz-Lara, Tomás; van de Ven, Glenn

2018-01-18

Supermassive black holes, with masses more than a million times that of the Sun, seem to inhabit the centres of all massive galaxies. Cosmologically motivated theories of galaxy formation require feedback from these supermassive black holes to regulate star formation. In the absence of such feedback, state-of-the-art numerical simulations fail to reproduce the number density and properties of massive galaxies in the local Universe. There is, however, no observational evidence of this strongly coupled coevolution between supermassive black holes and star formation, impeding our understanding of baryonic processes within galaxies. Here we report that the star formation histories of nearby massive galaxies, as measured from their integrated optical spectra, depend on the mass of the central supermassive black hole. Our results indicate that the black-hole mass scales with the gas cooling rate in the early Universe. The subsequent quenching of star formation takes place earlier and more efficiently in galaxies that host higher-mass central black holes. The observed relation between black-hole mass and star formation efficiency applies to all generations of stars formed throughout the life of a galaxy, revealing a continuous interplay between black-hole activity and baryon cooling.

The nature of the companion star in Circinus X-1

Science.gov (United States)

Johnston, Helen M.; Soria, Roberto; Gibson, Joel

2016-02-01

We present optical spectra and images of the X-ray binary Circinus X-1. The optical light curve of Cir X-1 is strongly variable, changing in brightness by 1.2 mag in the space of four days. The shape of the light curve is consistent with that seen in the 1980s, when the X-ray and radio counterparts of the source were at least ten times as bright as they are currently. We detect strong, variable H α emission lines, consisting of multiple components which vary with orbital phase. We estimate the extinction to the source from the strength of the diffuse interstellar bands and the Balmer decrement; the two methods give AV = 7.6 ± 0.6 mag and AV > 9.1 mag, respectively. The optical light curve can be modelled as arising from irradiation of the companion star by the central X-ray source, where a low-temperature star fills its Roche lobe in an orbit of moderate eccentricity (e ˜ 0.4). We suggest that the companion star is overluminous and underdense, due to the impact of the supernova which occurred less than 5000 yr ago.

Imprints of fast-rotating massive stars in the Galactic Bulge.

Science.gov (United States)

Chiappini, Cristina; Frischknecht, Urs; Meynet, Georges; Hirschi, Raphael; Barbuy, Beatriz; Pignatari, Marco; Decressin, Thibaut; Maeder, André

2011-04-28

The first stars that formed after the Big Bang were probably massive, and they provided the Universe with the first elements heavier than helium ('metals'), which were incorporated into low-mass stars that have survived to the present. Eight stars in the oldest globular cluster in the Galaxy, NGC 6522, were found to have surface abundances consistent with the gas from which they formed being enriched by massive stars (that is, with higher α-element/Fe and Eu/Fe ratios than those of the Sun). However, the same stars have anomalously high abundances of Ba and La with respect to Fe, which usually arises through nucleosynthesis in low-mass stars (via the slow-neutron-capture process, or s-process). Recent theory suggests that metal-poor fast-rotating massive stars are able to boost the s-process yields by up to four orders of magnitude, which might provide a solution to this contradiction. Here we report a reanalysis of the earlier spectra, which reveals that Y and Sr are also overabundant with respect to Fe, showing a large scatter similar to that observed in extremely metal-poor stars, whereas C abundances are not enhanced. This pattern is best explained as originating in metal-poor fast-rotating massive stars, which might point to a common property of the first stellar generations and even of the 'first stars'.

The coupling between pulsation and mass loss in massive stars

OpenAIRE

Townsend, Rich

2007-01-01

To what extent can pulsational instabilities resolve the mass-loss problem of massive stars? How important is pulsation in structuring and modulating the winds of these stars? What role does pulsation play in redistributing angular momentum in massive stars? Although I cannot offer answers to these questions, I hope at the very least to explain how they come to be asked.

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.

GRAVITATIONAL SLINGSHOT OF YOUNG MASSIVE STARS IN ORION

Energy Technology Data Exchange (ETDEWEB)

Chatterjee, Sourav; Tan, Jonathan C., E-mail: s.chatterjee@astro.ufl.edu, E-mail: jt@astro.ufl.edu [Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States)

2012-08-01

The Orion Nebula Cluster (ONC) is the nearest region of massive star formation and thus a crucial testing ground for theoretical models. Of particular interest among the ONC's {approx}1000 members are: {theta}{sup 1} Ori C, the most massive binary in the cluster with stars of masses 38 and 9 M{sub Sun }; the Becklin-Neugebauer (BN) object, a 30 km s{sup -1} runaway star of {approx}8 M{sub Sun }; and the Kleinmann-Low (KL) nebula protostar, a highly obscured, {approx}15 M{sub Sun} object still accreting gas while also driving a powerful, apparently 'explosive' outflow. The unusual behavior of BN and KL is much debated: How did BN acquire its high velocity? How is this related to massive star formation in the KL nebula? Here, we report the results of a systematic survey using {approx}10{sup 7} numerical experiments of gravitational interactions of the {theta}{sup 1}C and BN stars. We show that dynamical ejection of BN from this triple system at its observed velocity leaves behind a binary with total energy and eccentricity matching those observed for {theta}{sup 1}C. Five other observed properties of {theta}{sup 1}C are also consistent with it having ejected BN and altogether we estimate that there is only a {approx}< 10{sup -5} probability that {theta}{sup 1}C has these properties by chance. We conclude that BN was dynamically ejected from the {theta}{sup 1}C system about 4500 years ago. BN then plowed through the KL massive star-forming core within the last 1000 years causing its recently enhanced accretion and outflow activity.

Magnetic fields and massive star formation

Energy Technology Data Exchange (ETDEWEB)

Zhang, Qizhou; Keto, Eric; Ho, Paul T. P.; Ching, Tao-Chung; Chen, How-Huan [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Qiu, Keping [School of Astronomy and Space Science, Nanjing University, 22 Hankou Road, Nanjing 210093 (China); Girart, Josep M.; Juárez, Carmen [Institut de Ciències de l' Espai, (CSIC-IEEC), Campus UAB, Facultat de Ciències, C5p 2, E-08193 Bellaterra, Catalonia (Spain); Liu, Hauyu; Tang, Ya-Wen; Koch, Patrick M.; Rao, Ramprasad; Lai, Shih-Ping [Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 106, Taiwan (China); Li, Zhi-Yun [Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904 (United States); Frau, Pau [Observatorio Astronómico Nacional, Alfonso XII, 3 E-28014 Madrid (Spain); Li, Hua-Bai [Department of Physics, The Chinese University of Hong Kong, Hong Kong (China); Padovani, Marco [Laboratoire de Radioastronomie Millimétrique, UMR 8112 du CNRS, École Normale Supérieure et Observatoire de Paris, 24 rue Lhomond, F-75231 Paris Cedex 05 (France); Bontemps, Sylvain [OASU/LAB-UMR5804, CNRS, Université Bordeaux 1, F-33270 Floirac (France); Csengeri, Timea, E-mail: qzhang@cfa.harvard.edu [Max Planck Institute for Radioastronomy, Auf dem Hügel 69, D-53121 Bonn (Germany)

2014-09-10

Massive stars (M > 8 M {sub ☉}) typically form in parsec-scale molecular clumps that collapse and fragment, leading to the birth of a cluster of stellar objects. We investigate the role of magnetic fields in this process through dust polarization at 870 μm obtained with the Submillimeter Array (SMA). The SMA observations reveal polarization at scales of ≲0.1 pc. The polarization pattern in these objects ranges from ordered hour-glass configurations to more chaotic distributions. By comparing the SMA data with the single dish data at parsec scales, we found that magnetic fields at dense core scales are either aligned within 40° of or perpendicular to the parsec-scale magnetic fields. This finding indicates that magnetic fields play an important role during the collapse and fragmentation of massive molecular clumps and the formation of dense cores. We further compare magnetic fields in dense cores with the major axis of molecular outflows. Despite a limited number of outflows, we found that the outflow axis appears to be randomly oriented with respect to the magnetic field in the core. This result suggests that at the scale of accretion disks (≲ 10{sup 3} AU), angular momentum and dynamic interactions possibly due to close binary or multiple systems dominate over magnetic fields. With this unprecedentedly large sample of massive clumps, we argue on a statistical basis that magnetic fields play an important role during the formation of dense cores at spatial scales of 0.01-0.1 pc in the context of massive star and cluster star formation.

An unstable truth: how massive stars get their mass

Science.gov (United States)

Rosen, Anna L.; Krumholz, Mark R.; McKee, Christopher F.; Klein, Richard I.

2016-12-01

The pressure exerted by massive stars' radiation fields is an important mechanism regulating their formation. Detailed simulation of massive star formation therefore requires an accurate treatment of radiation. However, all published simulations have either used a diffusion approximation of limited validity; have only been able to simulate a single star fixed in space, thereby suppressing potentially important instabilities; or did not provide adequate resolution at locations where instabilities may develop. To remedy this, we have developed a new, highly accurate radiation algorithm that properly treats the absorption of the direct radiation field from stars and the re-emission and processing by interstellar dust. We use our new tool to perform 3D radiation-hydrodynamic simulations of the collapse of massive pre-stellar cores with laminar and turbulent initial conditions and properly resolve regions where we expect instabilities to grow. We find that mass is channelled to the stellar system via gravitational and Rayleigh-Taylor (RT) instabilities, in agreement with previous results using stars capable of moving, but in disagreement with methods where the star is held fixed or with simulations that do not adequately resolve the development of RT instabilities. For laminar initial conditions, proper treatment of the direct radiation field produces later onset of instability, but does not suppress it entirely provided the edges of radiation-dominated bubbles are adequately resolved. Instabilities arise immediately for turbulent pre-stellar cores because the initial turbulence seeds the instabilities. Our results suggest that RT features should be present around accreting massive stars throughout their formation.

The convective noise floor for the spectroscopic detection of low mass companions to solar type stars

Science.gov (United States)

Deming, D.; Espenak, F.; Jennings, D. E.; Brault, J. W.

1986-01-01

The threshold mass for the unambiguous spectroscopic detection of low mass companions to solar type stars is defined here as the time when the maximum acceleration in the stellar radial velocity due to the Doppler reflex of the companion exceeds the apparent acceleration produced by changes in convection. An apparent acceleration of 11 m/s/yr in integrated sunlight was measured using near infrared Fourier transform spectroscopy. This drift in the apparent solar velocity is attributed to a lessening in the magnetic inhibition of granular convection as solar minimum approaches. The threshold mass for spectroscopic detection of companions to a one solar mass star is estimated at below one Jupiter mass.

Massive runaway stars in the Large Magellanic Cloud

Science.gov (United States)

Gvaramadze, V. V.; Kroupa, P.; Pflamm-Altenburg, J.

2010-09-01

The origin of massive field stars in the Large Magellanic Cloud (LMC) has long been an enigma. The recent measurements of large offsets (˜ 100 km s-1) between the heliocentric radial velocities of some very massive (O2-type) field stars and the systemic LMC velocity provides a possible explanation of this enigma and suggests that the field stars are runaway stars ejected from their birthplaces at the very beginning of their parent cluster's dynamical evolution. A straightforward way to prove this explanation is to measure the proper motions of the field stars and to show that they are moving away from one of the nearby star clusters or OB associations. This approach is, however, complicated by the long distance to the LMC, which makes accurate proper motion measurements difficult. We used an alternative approach for solving the problem (first applied for Galactic field stars), based on the search for bow shocks produced by runaway stars. The geometry of detected bow shocks would allow us to infer the direction of stellar motion, thereby determining their possible parent clusters. In this paper we present the results of a search for bow shocks around six massive field stars that have been proposed as candidate runaway stars. Using archival Spitzer Space Telescope data, we found a bow shock associated with one of our programme stars, the O2 V((f*)) star BI 237, which is the first-ever detection of bow shocks in the LMC. Orientation of the bow shock suggests that BI 237 was ejected from the OB association LH 82 (located at ≃ 120 pc in projection from the star). A by-product of our search is the detection of bow shocks generated by four OB stars in the field of the LMC and an arc-like structure attached to the candidate luminous blue variable R81 (HD 269128). The geometry of two of these bow shocks is consistent with the possibility that their associated stars were ejected from the 30 Doradus star-forming complex. We discuss implications of our findings for the

BINARY DISRUPTION BY MASSIVE BLACK HOLES: HYPERVELOCITY STARS, S STARS, AND TIDAL DISRUPTION EVENTS

Energy Technology Data Exchange (ETDEWEB)

Bromley, Benjamin C. [Department of Physics and Astronomy, University of Utah, 115 S 1400 E, Rm 201, Salt Lake City, UT 84112 (United States); Kenyon, Scott J.; Geller, Margaret J.; Brown, Warren R., E-mail: bromley@physics.utah.edu, E-mail: skenyon@cfa.harvard.edu, E-mail: mgeller@cfa.harvard.edu, E-mail: wbrown@cfa.harvard.edu [Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States)

2012-04-20

We examine whether disrupted binary stars can fuel black hole growth. In this mechanism, tidal disruption produces a single hypervelocity star (HVS) ejected at high velocity and a former companion star bound to the black hole. After a cluster of bound stars forms, orbital diffusion allows the black hole to accrete stars by tidal disruption at a rate comparable to the capture rate. In the Milky Way, HVSs and the S star cluster imply similar rates of 10{sup -5} to 10{sup -3} yr{sup -1} for binary disruption. These rates are consistent with estimates for the tidal disruption rate in nearby galaxies and imply significant black hole growth from disrupted binaries on 10 Gyr timescales.

NGC 346: Looking in the Cradle of a Massive Star Cluster

Science.gov (United States)

Gouliermis, Dimitrios A.; Hony, Sacha

2017-03-01

How does a star cluster of more than few 10,000 solar masses form? We present the case of the cluster NGC 346 in the Small Magellanic Cloud, still embedded in its natal star-forming region N66, and we propose a scenario for its formation, based on observations of the rich stellar populations in the region. Young massive clusters host a high fraction of early-type stars, indicating an extremely high star formation efficiency. The Milky Way galaxy hosts several young massive clusters that fill the gap between young low-mass open clusters and old massive globular clusters. Only a handful, though, are young enough to study their formation. Moreover, the investigation of their gaseous natal environments suffers from contamination by the Galactic disk. Young massive clusters are very abundant in distant starburst and interacting galaxies, but the distance of their hosting galaxies do not also allow a detailed analysis of their formation. The Magellanic Clouds, on the other hand, host young massive clusters in a wide range of ages with the youngest being still embedded in their giant HII regions. Hubble Space Telescope imaging of such star-forming complexes provide a stellar sampling with a high dynamic range in stellar masses, allowing the detailed study of star formation at scales typical for molecular clouds. Our cluster analysis on the distribution of newly-born stars in N66 shows that star formation in the region proceeds in a clumpy hierarchical fashion, leading to the formation of both a dominant young massive cluster, hosting about half of the observed pre-main-sequence population, and a self-similar dispersed distribution of the remaining stars. We investigate the correlation between stellar surface density (and star formation rate derived from star-counts) and molecular gas surface density (derived from dust column density) in order to unravel the physical conditions that gave birth to NGC 346. A power law fit to the data yields a steep correlation between these

A Population Study of Wide-Separation Brown Dwarf Companions to Main Sequence Stars

Science.gov (United States)

Smith, Jeffrey J.

2005-01-01

Increased interest in infrared astronomy has opened the frontier to study cooler objects that shed significant light on the formation of planetary systems. Brown dwarf research provides a wealth of information useful for sorting through a myriad of proposed formation theories. Our study combines observational data from 2MASS with rigorous computer simulations to estimate the true population of long-range (greater than 1000 AU) brown dwarf companions in the solar neighborhood (less than 25 pc from Earth). Expanding on Gizis et al. (2001), we have found the margin of error in previous estimates to be significantly underestimated after we included orbit eccentricity, longitude of pericenter, angle of inclination, field star density, and primary and secondary luminosities as parameters influencing the companion systems in observational studies. We apply our simulation results to current L- and T-dwarf catalogs to provide updated estimates on the frequency of wide-separation brown dwarf companions to main sequence stars.

DISCOVERY OF A LOW-MASS COMPANION TO A METAL-RICH F STAR WITH THE MARVELS PILOT PROJECT

International Nuclear Information System (INIS)

Fleming, Scott W.; Ge Jian; Mahadevan, Suvrath; Lee, Brian; Cuong Nguyen, Duy; Morehead, Robert C.; Wan Xiaoke; Zhao Bo; Liu Jian; Guo Pengcheng; Kane, Stephen R.; Eastman, Jason D.; Siverd, Robert J.; Scott Gaudi, B.; Niedzielski, Andrzej; Sivarani, Thirupathi; Stassun, Keivan G.; Gary, Bruce; Wolszczan, Alex; Barnes, Rory

2010-01-01

We report the discovery of a low-mass companion orbiting the metal-rich, main sequence F star TYC 2949-00557-1 during the Multi-object APO Radial Velocity Exoplanet Large-area Survey (MARVELS) pilot project. The host star has an effective temperature T eff = 6135 ± 40 K, logg = 4.4 ± 0.1, and [Fe/H] = 0.32 ± 0.01, indicating a mass of M = 1.25 ± 0.09 M sun and R = 1.15 ± 0.15 R sun . The companion has an orbital period of 5.69449 ± 0.00023 days and straddles the hydrogen burning limit with a minimum mass of 64 M J , and thus may be an example of the rare class of brown dwarfs orbiting at distances comparable to those of 'Hot Jupiters'. We present relative photometry that demonstrates that the host star is photometrically stable at the few millimagnitude level on time scales of hours to years, and rules out transits for a companion of radius ∼>0.8 R J at the 95% confidence level. Tidal analysis of the system suggests that the star and companion are likely in a double synchronous state where both rotational and orbital synchronization have been achieved. This is the first low-mass companion detected with a multi-object, dispersed, fixed-delay interferometer.

RETIRED A STARS AND THEIR COMPANIONS. VII. 18 NEW JOVIAN PLANETS

International Nuclear Information System (INIS)

Johnson, John Asher; Clanton, Christian; Crepp, Justin R.; Howard, Andrew W.; Marcy, Geoffrey W.; Bowler, Brendan P.; Isaacson, Howard; Henry, Gregory W.; Endl, Michael; Cochran, William D.; MacQueen, Phillip J.; Wright, Jason T.

2011-01-01

We report the detection of 18 Jovian planets discovered as part of our Doppler survey of subgiant stars at Keck Observatory, with follow-up Doppler and photometric observations made at McDonald and Fairborn Observatories, respectively. The host stars have masses 0.927 ≤ M * /M ☉ ≤ 1.95, radii 2.5 ≤ R * /R ☉ ≤ 8.7, and metallicities –0.46 ≤ [Fe/H] ≤+0.30. The planets have minimum masses 0.9 M Jup ≤ M P sin i ∼ Jup and semimajor axes a ≥ 0.76 AU. These detections represent a 50% increase in the number of planets known to orbit stars more massive than 1.5 M ☉ and provide valuable additional information about the properties of planets around stars more massive than the Sun.

The low-metallicity starburst NGC346: massive-star population and feedback

Science.gov (United States)

Oskinova, Lida

2017-08-01

The Small Magellanic Cloud (SMC) is ideal to study young, massive stars at low metallicity. The compact cluster NGC346 contains about half of all O-type stars in the entire SMC. The massive-star population of this cluster powers N66, the brightest and largest HII region in the SMC. We propose to use HST-STIS to slice NGC346 with 20 long-slit exposures, in order to obtain the UV spectra of most of the massive early-type stars of this cluster. Archival data of 13 exposures that cover already a minor part of this cluster will be included in our analyses. Our aim is to quantitatively analyze virtually the whole massive-star population of NGC346. We have already secured the optical spectra of all massive stars in the field with the integral-field spectrograph MUSE at the ESO-VLT. However, for the determination of the stellar-wind parameters, i.e. the mass-loss rates and the wind velocities, ultraviolet spectra are indispensable. Our advanced Potsdam Wolf-Rayet (PoWR) code will be used for modeling the stellar and wind spectra in the course of the analysis. Finally, we will obtain:(a) the fundamental stellar and wind parameters of all stars brighter than spectral type B2V in the field, which, e,g,, will constrain the initial mass function in this young low-metallicity starburst;(b) mass-loss rates of many more OB-type stars at SMC metallicity than hitherto known, allowing to better constrain their metallicity dependence;(c) the integrated feedback by ionizing radiation and stellar winds of the whole massive-star population of NGC346, which will be used as input to model the ecology of the giant HII region N66.These HST UV data will be of high legacy value.

Massive Star Burps, Then Explodes

Science.gov (United States)

2007-04-01

Berkeley -- In a galaxy far, far away, a massive star suffered a nasty double whammy. On Oct. 20, 2004, Japanese amateur astronomer Koichi Itagaki saw the star let loose an outburst so bright that it was initially mistaken for a supernova. The star survived, but for only two years. On Oct. 11, 2006, professional and amateur astronomers witnessed the star actually blowing itself to smithereens as Supernova 2006jc. Swift UVOT Image Swift UVOT Image (Credit: NASA / Swift / S.Immler) "We have never observed a stellar outburst and then later seen the star explode," says University of California, Berkeley, astronomer Ryan Foley. His group studied the event with ground-based telescopes, including the 10-meter (32.8-foot) W. M. Keck telescopes in Hawaii. Narrow helium spectral lines showed that the supernova's blast wave ran into a slow-moving shell of material, presumably the progenitor's outer layers ejected just two years earlier. If the spectral lines had been caused by the supernova's fast-moving blast wave, the lines would have been much broader. artistic rendering This artistic rendering depicts two years in the life of a massive blue supergiant star, which burped and spewed a shell of gas, then, two years later, exploded. When the supernova slammed into the shell of gas, X-rays were produced. (Credit: NASA/Sonoma State Univ./A.Simonnet) Another group, led by Stefan Immler of NASA's Goddard Space Flight Center, Greenbelt, Md., monitored SN 2006jc with NASA's Swift satellite and Chandra X-ray Observatory. By observing how the supernova brightened in X-rays, a result of the blast wave slamming into the outburst ejecta, they could measure the amount of gas blown off in the 2004 outburst: about 0.01 solar mass, the equivalent of about 10 Jupiters. "The beautiful aspect of our SN 2006jc observations is that although they were obtained in different parts of the electromagnetic spectrum, in the optical and in X-rays, they lead to the same conclusions," says Immler. "This

NO NEUTRON STAR COMPANION TO THE LOWEST MASS SDSS WHITE DWARF

International Nuclear Information System (INIS)

Agueeros, Marcel A.; Camilo, Fernando; Heinke, Craig; Kilic, Mukremin; Anderson, Scott F.; Silvestri, Nicole M.; Freire, Paulo; Kleinman, Scot J.; Liebert, James W.

2009-01-01

SDSS J091709.55+463821.8 (hereafter J0917+4638) is the lowest surface gravity white dwarf (WD) currently known, with log g = 5.55 ± 0.05 (M ∼ 0.17 M sun ). Such low-mass white dwarfs (LMWDs) are believed to originate in binaries that evolve into WD/WD or WD/neutron star (NS) systems. An optical search for J0917+4638's companion showed that it must be a compact object with a mass ≥0.28 M sun . Here we report on Green Bank Telescope 820 MHz and XMM-Newton X-ray observations of J0917+4638 intended to uncover a potential NS companion to the LMWD. No convincing pulsar signal is detected in our radio data. Our X-ray observation also failed to detect X-ray emission from J0917+4638's companion, while we would have detected any of the millisecond radio pulsars in 47 Tuc. We conclude that the companion is almost certainly another WD.

A likely candidate of type Ia supernova progenitors: the X-ray pulsating companion of the hot subdwarf HD 49798

International Nuclear Information System (INIS)

Wang Bo; Han Zhanwen

2010-01-01

HD 49798 is a hydrogen depleted subdwarf O6 star and has an X-ray pulsating companion (RX J0648.0-4418). The X-ray pulsating companion is a massive white dwarf. Employing Eggleton's stellar evolution code with the optically thick wind assumption, we find that the hot subdwarf HD 49798 and its X-ray pulsating companion could produce a type Ia supernova (SN Ia) in future evolution. This implies that the binary system is a likely candidate of an SN Ia progenitor. We also discuss the possibilities of some other WD + He star systems (e.g. V445 Pup and KPD 1930+2752) for producing SNe Ia. (research papers)

THE VERY MASSIVE STAR CONTENT OF THE NUCLEAR STAR CLUSTERS IN NGC 5253

Energy Technology Data Exchange (ETDEWEB)

Smith, L. J. [Space Telescope Science Institute and European Space Agency, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Crowther, P. A. [Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH (United Kingdom); Calzetti, D. [Department of Astronomy, University of Massachusetts—Amherst, Amherst, MA 01003 (United States); Sidoli, F., E-mail: lsmith@stsci.edu [London Centre for Nanotechnology, University College London, London WC1E 6BT (United Kingdom)

2016-05-20

The blue compact dwarf galaxy NGC 5253 hosts a very young starburst containing twin nuclear star clusters, separated by a projected distance of 5 pc. One cluster (#5) coincides with the peak of the H α emission and the other (#11) with a massive ultracompact H ii region. A recent analysis of these clusters shows that they have a photometric age of 1 ± 1 Myr, in apparent contradiction with the age of 3–5 Myr inferred from the presence of Wolf-Rayet features in the cluster #5 spectrum. We examine Hubble Space Telescope ultraviolet and Very Large Telescope optical spectroscopy of #5 and show that the stellar features arise from very massive stars (VMSs), with masses greater than 100 M {sub ⊙}, at an age of 1–2 Myr. We further show that the very high ionizing flux from the nuclear clusters can only be explained if VMSs are present. We investigate the origin of the observed nitrogen enrichment in the circumcluster ionized gas and find that the excess N can be produced by massive rotating stars within the first 1 Myr. We find similarities between the NGC 5253 cluster spectrum and those of metal-poor, high-redshift galaxies. We discuss the presence of VMSs in young, star-forming galaxies at high redshift; these should be detected in rest-frame UV spectra to be obtained with the James Webb Space Telescope . We emphasize that population synthesis models with upper mass cutoffs greater than 100 M {sub ⊙} are crucial for future studies of young massive star clusters at all redshifts.

Massive Stars as Progenitors of Supernovae and GRBs

NARCIS (Netherlands)

Langer, N.; van Marle, A.J.; Poelarends, A.J.T.; Yoon, S.C.

2007-01-01

The evolutionary fate of massive stars in our Milky Way is thought to be reasonably well understood: stars above ˜ 8 M_o produce neutron stars and supernovae, while those above ˜ 20...30 M_o are presumed to form black holes. At metallicities below that of the SMC, however, our knowledge becomes

Multi-wavelength investigations on feedback of massive star formation

Science.gov (United States)

Yuan, Jinghua

2014-05-01

In the course of massive star formation, outflows, ionizing radiation and intense stellar winds could heavily affect their adjacent environs and natal clouds. There are several outstanding open questions related to these processes: i) whether they can drive turbulence in molecular clouds; ii) whether they are able to trigger star formation; iii) whether they can destroy natal clouds to terminate star formation at low efficiencies. This thesis investigates feedback in different stages of massive star formation. Influence of such feedback to the ambient medium has been revealed. A new type of millimeter methanol maser is detected for the first time. An uncommon bipolar outflow prominent in the mid-infrared is discovered. And features of triggered star formation are found on the border of an infrared bubble and in the surroundings of a Herbig Be star. Extended green objects (EGOs) are massive outflow candidates showing prominent shocked features in the mid-infrared. We have carried out a high resolution study of the EGO G22.04+0.22 (hereafter, G22) based on archived SMA data. Continuum and molecular lines at 1.3 mm reveal that G22 is still at a hot molecular core stage. A very young multi-polar outflow system is detected, which is interacting with the adjacent dense gas. Anomalous emission features from CH3OH (8,-1,8 - 7,0,7) and CH3OH (4,2,2 - 3,1,2) are proven to be millimeter masers. It is the first time that maser emission of CH3OH (8,-1,8 - 7,0,7) at 218.440 GHz is detected in a massive star-forming region. Bipolar outflows have been revealed and investigated almost always in the microwave or radio domain. It's sort of rare that hourglass-shaped morphology be discovered in the mid-infrared. Based on GLIMPSE data, we have discovered a bipolar object resembling an hourglass at 8.0 um. It is found to be associated with IRAS 18114-1825. Analysis based on fitted SED, optical spectroscopy, and infrared color indices suggests IRAS 18114-1825 is an uncommon bipolar

Metallicity dependence of envelope inflation in massive stars

Czech Academy of Sciences Publication Activity Database

Sanyal, D.; Langer, N.; Szécsi, Dorottya; Yoon, S.-C.; Grassitelli, L.

2017-01-01

Roč. 597, January (2017), A71/1-A71/16 E-ISSN 1432-0746 R&D Projects: GA ČR(CZ) GA14-02385S Institutional support: RVO:67985815 Keywords : stars evolution * stars massive * stars interiors Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics OBOR OECD: Astronomy (including astrophysics,space science) Impact factor: 5.014, year: 2016

Formation and pre-MS Evolution of Massive Stars with Growing Accretion

Science.gov (United States)

Maeder, A.; Behrend, R.

2002-10-01

We briefly describe the three existing scenarios for forming massive stars and emphasize that the arguments often used to reject the accretion scenario for massive stars are misleading. It is usually not accounted for the fact that the turbulent pressure associated to large turbulent velocities in clouds necessarily imply relatively high accretion rates for massive stars. We show the basic difference between the formation of low and high mass stars based on the values of the free fall time and of the Kelvin-Helmholtz timescale, and define the concept of birthline for massive stars. Due to D-burning, the radius and location of the birthline in the HR diagram, as well as the lifetimes are very sensitive to the accretion rate dM/dt(accr). If a form dM/dt(accr) propto A(M/Msun)phi is adopted, the observations in the HR diagram and the lifetimes support a value of A approx 10-5 Msun/yr and a value of phi > 1. Remarkably, such a law is consistent with the relation found by Churchwell and Henning et al. between the outflow rates and the luminosities of ultracompact HII regions, if we assume that a fraction 0.15 to 0.3 of the global inflow is accreted. The above relation implies high dM/dt(accr) approx 10-3 Msun/yr for the most massive stars. The physical possibility of such high dM/dt(accr) is supported by current numerical models. Finally, we give simple analytical arguments in favour of the growth of dM/dt(accr) with the already accreted mass. We also suggest that due to Bondi-Hoyle accretion, the formation of binary stars is largely favoured among massive stars in the accretion scenario.

Confronting Models of Massive Star Evolution and Explosions with Remnant Mass Measurements

Science.gov (United States)

Raithel, Carolyn A.; Sukhbold, Tuguldur; Özel, Feryal

2018-03-01

The mass distribution of compact objects provides a fossil record that can be studied to uncover information on the late stages of massive star evolution, the supernova explosion mechanism, and the dense matter equation of state. Observations of neutron star masses indicate a bimodal Gaussian distribution, while the observed black hole mass distribution decays exponentially for stellar-mass black holes. We use these observed distributions to directly confront the predictions of stellar evolution models and the neutrino-driven supernova simulations of Sukhbold et al. We find strong agreement between the black hole and low-mass neutron star distributions created by these simulations and the observations. We show that a large fraction of the stellar envelope must be ejected, either during the formation of stellar-mass black holes or prior to the implosion through tidal stripping due to a binary companion, in order to reproduce the observed black hole mass distribution. We also determine the origins of the bimodal peaks of the neutron star mass distribution, finding that the low-mass peak (centered at ∼1.4 M ⊙) originates from progenitors with M ZAMS ≈ 9–18 M ⊙. The simulations fail to reproduce the observed peak of high-mass neutron stars (centered at ∼1.8 M ⊙) and we explore several possible explanations. We argue that the close agreement between the observed and predicted black hole and low-mass neutron star mass distributions provides new, promising evidence that these stellar evolution and explosion models capture the majority of relevant stellar, nuclear, and explosion physics involved in the formation of compact objects.

Formation of massive stars in OB associations and giant molecular clouds

International Nuclear Information System (INIS)

Lada, C.J.

1980-01-01

Certain interesting patterns are being perceived in the morphology of the regions which have recently produced massive OB stars. In particular, current evidence seems to favour the notion that the formation of massive stars takes place at the edges and not the centres of large molecular cloud complexes. It is this aspect of the observations that is discussed in the present paper. The phenomena described here will pertain to massive stars only. Specifically, stars with spectral types earlier than B3 will be considered since it is usually only these stars that produce sufficient havoc (e.g., maser sources, CO bright spots, H II regions) to noticeably affect their early environments. The corresponding phenomena for lower mass stars could be entirely different. A review is first presented of what has been learned about the OB star formation process from studies of the visible OB stars themselves. Then, newly derived information pertaining to the most recent episodes of OB star birth in galactic molecular clouds is discussed. Finally, a short discussion of the significance of the results and their implications for possible star formation mechanisms will be made. (U.K.)

A SUBSTELLAR COMMON PROPER-MOTION COMPANION TO THE PLEIAD H II 1348

International Nuclear Information System (INIS)

Geißler, Kerstin; Metchev, Stanimir A.; Pham, Alfonse; Larkin, James E.; McElwain, Michael; Hillenbrand, Lynne A.

2012-01-01

We announce the identification of a proper-motion companion to the star H II 1348, a K5 V member of the Pleiades open cluster. The existence of a faint point source 1.''1 away from H II 1348 was previously known from adaptive optics imaging by Bouvier et al. However, because of a high likelihood of background star contamination and in the absence of follow-up astrometry, Bouvier et al. tentatively concluded that the candidate companion was not physically associated with H II 1348. We establish the proper-motion association of the pair from adaptive optics imaging with the Palomar 5 m telescope. Adaptive optics spectroscopy with the integral field spectrograph OSIRIS on the Keck 10 m telescope reveals that the companion has a spectral type of M8 ± 1. According to substellar evolution models, the M8 spectral type resides within the substellar mass regime at the age of the Pleiades. The primary itself is a known double-lined spectroscopic binary, which makes the resolved companion, H II 1348B, the least massive and widest component of this hierarchical triple system and the first substellar companion to a stellar primary in the Pleiades.

The incidence of stellar mergers and mass gainers among massive stars

International Nuclear Information System (INIS)

De Mink, S. E.; Sana, H.; Langer, N.; Izzard, R. G.; Schneider, F. R. N.

2014-01-01

Because the majority of massive stars are born as members of close binary systems, populations of massive main-sequence stars contain stellar mergers and products of binary mass transfer. We simulate populations of massive stars accounting for all major binary evolution effects based on the most recent binary parameter statistics and extensively evaluate the effect of model uncertainties. Assuming constant star formation, we find that 8 −4 +9 % of a sample of early-type stars are the products of a merger resulting from a close binary system. In total we find that 30 −15 +10 % of massive main-sequence stars are the products of binary interaction. We show that the commonly adopted approach to minimize the effects of binaries on an observed sample by excluding systems detected as binaries through radial velocity campaigns can be counterproductive. Systems with significant radial velocity variations are mostly pre-interaction systems. Excluding them substantially enhances the relative incidence of mergers and binary products in the non-radial velocity variable sample. This poses a challenge for testing single stellar evolutionary models. It also raises the question of whether certain peculiar classes of stars, such as magnetic O stars, are the result of binary interaction and it emphasizes the need to further study the effect of binarity on the diagnostics that are used to derive the fundamental properties (star-formation history, initial mass function, mass-to-light ratio) of stellar populations nearby and at high redshift.

HST/STIS ULTRAVIOLET SPECTROSCOPY OF THE COMPONENTS OF THE MASSIVE TRIPLE STAR δ ORI A

Energy Technology Data Exchange (ETDEWEB)

Richardson, Noel D.; Moffat, Anthony F. J. [Département de physique and Centre de Recherche en Astrophysique du Québec (CRAQ), Université de Montréal, C.P. 6128, Succ. Centre-Ville, Montréal, Québec, H3C 3J7 (Canada); Gull, Theodore R.; Lindler, Don J. [Astrophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Gies, Douglas R. [Center for High Angular Resolution Astronomy and Department of Physics and Astronomy, Georgia State University, P.O. Box 5060, Atlanta, GA 30302-5060 (United States); Corcoran, Michael F. [CRESST and X-ray Astrophysics Laboratory NASA/GSFC, Greenbelt, MD 20771 (United States); Chené, André-Nicolas, E-mail: richardson@astro.umontreal.ca, E-mail: moffat@astro.umontreal.ca, E-mail: theodore.r.gull@nasa.gov, E-mail: don.j.lindler@nasa.gov, E-mail: gies@chara.gsu.edu, E-mail: michael.f.corcoran@nasa.gov, E-mail: achene@gemini.edu [Gemini Observatory, Northern Operations Center, 670 North A’ohoku Place, Hilo, HI 96720 (United States)

2015-07-20

The multiple star system of δ Orionis is one of the closest examples of a system containing a luminous O-type, bright giant star (component Aa1). It is often used as a spectral-type standard and has the highest observed X-ray flux of any hot-star binary. The main component Aa1 is orbited by two lower mass stars, faint Aa2 in a 5.7 day eclipsing binary, and Ab, an astrometric companion with an estimated period of 346 years. Generally the flux from all three stars is recorded in ground-based spectroscopy, and the spectral decomposition of the components has proved difficult. Here we present Hubble Space Telescope/Space Telescope Imaging Spectrograph ultraviolet spectroscopy of δ Ori A that provides us with spatially separated spectra of Aa and Ab for the first time. We measured radial velocities for Aa1 and Ab in two observations made near the velocity extrema of Aa1. We show tentative evidence for the detection of the Aa2 component in cross-correlation functions of the observed and model spectra. We discuss the appearance of the UV spectra of Aa1 and Ab with reference to model spectra. Both stars have similar effective temperatures, but Ab is fainter and is a rapid rotator. The results will help in the interpretation of ground-based spectroscopy and in understanding the physical and evolutionary parameters of these massive stars.

Evidence of a massive planet candidate orbiting the young active K5V star BD+20 1790

Science.gov (United States)

Hernán-Obispo, M.; Gálvez-Ortiz, M. C.; Anglada-Escudé, G.; Kane, S. R.; Barnes, J. R.; de Castro, E.; Cornide, M.

2010-03-01

Context. BD+20 1790 is a young active, metal-rich, late-type K5Ve star. We have undertaken a study of stellar activity and kinematics for this star over the past few years. Previous results show a high level of stellar activity, with the presence of prominence-like structures, spots on the surface, and strong flare events, despite the moderate rotational velocity of the star. In addition, radial velocity variations with a semi-amplitude of up to 1 km s-1 were detected. Aims: We investigate the nature of these radial velocity variations, in order to determine whether they are due to stellar activity or the reflex motion of the star induced by a companion. Methods: We have analysed high-resolution echelle spectra by measuring stellar activity indicators and computing radial velocity (RV) and bisector velocity spans. Two-band photometry was also obtained to produce the light curve and determine the photometric period. Results: Based upon the analysis of the bisector velocity span, as well as spectroscopic indices of chromospheric indicators, Ca ii H & K, Hα, and taking the photometric analysis into account, we report that the best explanation for the RV variation is the presence of a substellar companion. The Keplerian fit of the RV data yields a solution for a close-in massive planet with an orbital period of 7.78 days. The presence of the close-in massive planet could also be an interpretation for the high level of stellar activity detected. Since the RV data are not part of a planet search programme, we can consider our results as a serendipitous evidence of a planetary companion. To date, this is the youngest main sequence star for which a planetary candidate has been reported. Based on observations collected at the German-Spanish Astronomical Center, Calar Alto, jointly operated by the Max-Planck-Institut für Astronomie Heidelberg and the Instituto de Astrofísica de Andalucía (CSIC). Based on observations made with the Italian Telescopio Nazionale Galileo

B fields in OB stars (BOB): Low-resolution FORS2 spectropolarimetry of the first sample of 50 massive stars

NARCIS (Netherlands)

Fossati, L.; Castro, N.; Schöller, M.; Hubrig, S.; Langer, N.; Morel, T.; Briquet, M.; Herrero, A.; Przybilla, N.; Sana, H.; Schneider, F.R.N.; de Koter, A.

2015-01-01

Within the context of the collaboration "B fields in OB stars" (BOB), we used the FORS2 low-resolution spectropolarimeter to search for a magnetic field in 50 massive stars, including two reference magnetic massive stars. Because of the many controversies of magnetic field detections obtained with

HAT-P-13b,c: A TRANSITING HOT JUPITER WITH A MASSIVE OUTER COMPANION ON AN ECCENTRIC ORBIT

International Nuclear Information System (INIS)

Bakos, G. A.; Noyes, R. W.; Hartman, J.; Torres, G.; Latham, D. W.; Sasselov, D. D.; Stefanik, R. P.; Sipocz, B.; Kovacs, Gabor; Esquerdo, G. A.; Pal, A.; Howard, A. W.; Marcy, G. W.; Kovacs, Geza; Fischer, D. A.; Johnson, J. A.; Lazar, J.; Papp, I.; Sari, P.

2009-01-01

We report on the discovery of a planetary system with a close-in transiting hot Jupiter on a near circular orbit and a massive outer planet on a highly eccentric orbit. The inner planet, HAT-P-13b, transits the bright V = 10.622 G4 dwarf star GSC 3416 - 00543 every P = 2.916260 ± 0.000010 days, with transit epoch T c = 2454779.92979 ± 0.00038 (BJD) and duration 0.1345 ± 0.0017 days. The outer planet HAT-P-13c orbits the star every P 2 = 428.5 ± 3.0 days with a nominal transit center (assuming zero impact parameter) of T 2c = 2454870.4 ± 1.8 (BJD) or time of periastron passage T 2,peri = 2454890.05 ± 0.48 (BJD). Transits of the outer planet have not been observed, and may not be present. The host star has a mass of 1.22 +0.05 -0.10 M sun , radius of 1.56 ± 0.08 R sun , effective temperature of 5653 ± 90 K, and is rather metal-rich with [Fe/H] = +0.41 ± 0.08. The inner planetary companion has a mass of 0.853 +0.029 -0.046 M J , and radius of 1.281 ± 0.079 R J , yielding a mean density of 0.498 +0.103 -0.069 g cm -3 . The outer companion has m 2 sin i 2 = 15.2 ± 1.0 M J , and orbits on a highly eccentric orbit of e 2 = 0.691 ± 0.018. While we have not detected significant transit timing variations of HAT-P-13b, due to gravitational and light-travel time effects, future observations will constrain the orbital inclination of HAT-P-13c, along with its mutual inclination to HAT-P-13b. The HAT-P-13 (b, c) double-planet system may prove extremely valuable for theoretical studies of the formation and dynamics of planetary systems.

One of the most massive stars in the Galaxy may have formed in isolation

OpenAIRE

Oskinova, L. M.; Steinke, M.; Hamann, W. -R.; Sander, A.; Todt, H.; Liermann, A.

2013-01-01

Very massive stars, 100 times heavier than the sun, are rare. It is not yet known whether such stars can form in isolation or only in star clusters. The answer to this question is of fundamental importance. The central region of our Galaxy is ideal for investigating very massive stars and clusters located in the same environment. We used archival infrared images to investigate the surroundings of apparently isolated massive stars presently known in the Galactic Center. We find that two such i...

Small scale kinematics of massive star-forming cores

NARCIS (Netherlands)

Wang, Kuo-Song

2013-01-01

Unlike the formation of Solar-type stars, the formation of massive stars (M>8 Msun) is not yet well understood. For Solar-type protostars, the presence of circumstellar or protoplanetary disks which provide a path for mass accretion onto protostars is well established. However, to date only few

Discovery of a wide planetary-mass companion to the young M3 star GU PSC

Energy Technology Data Exchange (ETDEWEB)

Naud, Marie-Eve; Artigau, Étienne; Malo, Lison; Albert, Loïc; Doyon, René; Lafrenière, David; Gagné, Jonathan; Boucher, Anne [Département de physique and Observatoire du Mont-Mégantic, Université de Montréal, Montréal H3C 3J7 (Canada); Saumon, Didier [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Morley, Caroline V. [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Allard, France; Homeier, Derek [Centre de Recherche Astrophysique de Lyon, UMR 5574 CNRS, Université de Lyon, École Normale Supérieure de Lyon, 46 Allée d' Italie, F-69364 Lyon Cedex 07 (France); Beichman, Charles A.; Gelino, Christopher R., E-mail: naud@astro.umontreal.ca [Infrared Processing and Analysis Center, MS 100-22, California Institute of Technology, Pasadena, CA 91125 (United States)

2014-05-20

We present the discovery of a comoving planetary-mass companion ∼42'' (∼2000 AU) from a young M3 star, GU Psc, a likely member of the young AB Doradus Moving Group (ABDMG). The companion was first identified via its distinctively red i – z color (>3.5) through a survey made with Gemini-S/GMOS. Follow-up Canada-France-Hawaii Telescope/WIRCam near-infrared (NIR) imaging, Gemini-N/GNIRS NIR spectroscopy and Wide-field Infrared Survey Explorer photometry indicate a spectral type of T3.5 ± 1 and reveal signs of low gravity which we attribute to youth. Keck/Adaptive Optics NIR observations did not resolve the companion as a binary. A comparison with atmosphere models indicates T {sub eff} = 1000-1100 K and log g = 4.5-5.0. Based on evolution models, this temperature corresponds to a mass of 9-13 M {sub Jup} for the age of ABDMG (70-130 Myr). The relatively well-constrained age of this companion and its very large angular separation to its host star will allow its thorough characterization and will make it a valuable comparison for planetary-mass companions that will be uncovered by forthcoming planet-finder instruments such as Gemini Planet Imager and SPHERE 9.

The Evolution of Massive Stars: a Selection of Facts and Questions

Science.gov (United States)

Vanbeveren, D.

In the present paper we discuss a selection of facts and questions related to observations and evolutionary calculations of massive single stars and massive stars in interacting binaries. We focus on the surface chemical abundances, the role of stellar winds, the early Be-stars, the high mass X-ray binaries and the effects of rotation on stellar evolution. Finally, we present an unconventionally formed object scenario (UFO-scenario) of WR binaries in dense stellar environments.

X-RAY EMISSION FROM MAGNETIC MASSIVE STARS

International Nuclear Information System (INIS)

Nazé, Yaël; Petit, Véronique; Rinbrand, Melanie; Owocki, Stan; Cohen, David; Ud-Doula, Asif; Wade, Gregg A.

2014-01-01

Magnetically confined winds of early-type stars are expected to be sources of bright and hard X-rays. To clarify the systematics of the observed X-ray properties, we have analyzed a large series of Chandra and XMM-Newton observations, corresponding to all available exposures of known massive magnetic stars (over 100 exposures covering ∼60% of stars compiled in the catalog of Petit et al.). We show that the X-ray luminosity is strongly correlated with the stellar wind mass-loss rate, with a power-law form that is slightly steeper than linear for the majority of the less luminous, lower- M-dot B stars and flattens for the more luminous, higher- M-dot O stars. As the winds are radiatively driven, these scalings can be equivalently written as relations with the bolometric luminosity. The observed X-ray luminosities, and their trend with mass-loss rates, are well reproduced by new MHD models, although a few overluminous stars (mostly rapidly rotating objects) exist. No relation is found between other X-ray properties (plasma temperature, absorption) and stellar or magnetic parameters, contrary to expectations (e.g., higher temperature for stronger mass-loss rate). This suggests that the main driver for the plasma properties is different from the main determinant of the X-ray luminosity. Finally, variations of the X-ray hardnesses and luminosities, in phase with the stellar rotation period, are detected for some objects and they suggest that some temperature stratification exists in massive stars' magnetospheres

Massive stars on the verge of exploding: the properties of oxygen sequence Wolf-Rayet stars

NARCIS (Netherlands)

Tramper, F.; Straal, S.M.; Sanyal, D.; Sana, H.; de Koter, A.; Gräfener, G.; Langer, N.; Vink, J.S.; de Mink, S.E.; Kaper, L.

2015-01-01

Context. Oxygen sequence Wolf-Rayet (WO) stars are a very rare stage in the evolution of massive stars. Their spectra show strong emission lines of helium-burning products, in particular highly ionized carbon and oxygen. The properties of WO stars can be used to provide unique constraints on the

Stellar Feedback in Massive Star-Forming Regions

Science.gov (United States)

Baldwin, Jack; Pellegrini, Eric; Ferland, Gary; Murray, Norm; Hanson, Margaret

2008-02-01

Star formation rates and chemical evolution are controlled in part by the interaction of stellar radiation and winds with the remnant molecular gas from which the stars have formed. We are carrying out a detailed, panchromatic study in the two nearest giant star-forming regions to nail down the physics that produces the 10-20 parsec bubbles seen to surround young massive clusters in the Milky Way. This will determine if and how the clusters disrupt their natal giant molecular clouds (GMCs). Here we request 4 nights on the Blanco telescope to obtain dense grids of optical long-slit spectra criss-crossing each nebula. These will cover the [S II] doublet (to measure N_e) and also [O III], H(beta), [O I], H(alpha) and [N II] to measure the ionization mechanism and ionization parameter, at ~3000 different spots in each nebula. From this we can determine a number of dynamically important quantities, such as the gas density and temperature, hence pressure in and around these bubbles. These quantities can be compared to the dynamical (gravitationally induced) pressure, and the radiation pressure. All can be employed in dynamical models for the evolution of a GMC under the influence of an embedded massive star cluster. This research will elucidate the detailed workings of the star-forming regions which dominate the star formation rate in the Milky Way, and also will steadily improve our calibration and understanding of more distant, less well-resolved objects such as ULIRGS, Lyman break, and submillimeter galaxies.

FRIENDS OF HOT JUPITERS. II. NO CORRESPONDENCE BETWEEN HOT-JUPITER SPIN-ORBIT MISALIGNMENT AND THE INCIDENCE OF DIRECTLY IMAGED STELLAR COMPANIONS

Energy Technology Data Exchange (ETDEWEB)

Ngo, Henry; Knutson, Heather A.; Hinkley, Sasha; Batygin, Konstantin [Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA (United States); Crepp, Justin R.; Bechter, Eric B. [Department of Physics, University of Notre Dame, Notre Dame, IN (United States); Howard, Andrew W. [Institute for Astronomy, University of Hawaii at Manoa, Honolulu, HI (United States); Johnson, John A. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States); Morton, Timothy D. [Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA (United States); Muirhead, Philip S., E-mail: hngo@caltech.edu [Department of Astronomy, Boston University, Boston, MA (United States)

2015-02-20

Multi-star systems are common, yet little is known about a stellar companion's influence on the formation and evolution of planetary systems. For instance, stellar companions may have facilitated the inward migration of hot Jupiters toward to their present day positions. Many observed short-period gas giant planets also have orbits that are misaligned with respect to their star's spin axis, which has also been attributed to the presence of a massive outer companion on a non-coplanar orbit. We present the results of a multi-band direct imaging survey using Keck NIRC2 to measure the fraction of short-period gas giant planets found in multi-star systems. Over three years, we completed a survey of 50 targets ('Friends of Hot Jupiters') with 27 targets showing some signature of multi-body interaction (misaligned or eccentric orbits) and 23 targets in a control sample (well-aligned and circular orbits). We report the masses, projected separations, and confirmed common proper motion for the 19 stellar companions found around 17 stars. Correcting for survey incompleteness, we report companion fractions of 48% ± 9%, 47% ± 12%, and 51% ± 13% in our total, misaligned/eccentric, and control samples, respectively. This total stellar companion fraction is 2.8σ larger than the fraction of field stars with companions approximately 50-2000 AU. We observe no correlation between misaligned/eccentric hot Jupiter systems and the incidence of stellar companions. Combining this result with our previous radial velocity survey, we determine that 72% ± 16% of hot Jupiters are part of multi-planet and/or multi-star systems.

PSR 1913 + 16: endpoints of speculation. A critical discussion of possible companions and progenitors

Energy Technology Data Exchange (ETDEWEB)

Webbink, R F [Cambridge Univ. (UK). Inst. of Astronomy

1975-01-01

We attempt a comprehensive discussion of the nature and origin of the binary pulsar PSR 1913 + 16. It is shown that the system must have been binary before the creation of the pulsar. Main-sequence stars, white dwarfs, helium stars, neutron stars and black holes are considered as possible secondaries. It is shown that the pulsar component must have been a helium star before collapse. The companion is probably a neutron star, although a helium star or black hole cannot be excluded. We suggest that the pulsar was formed when a moderately massive (2 to 8 M(S)) helium star overfilled its Roche lobe and was stripped of its helium-rich envelope. Core collapse and carbon ignition followed rapidly, creating the neutron star we observe.

Observational tests for the evolution of massive stars in nearby galaxies

International Nuclear Information System (INIS)

Leitherer, C.

1990-01-01

Population synthesis calculations applicable to the massive stellar content in nearby galaxies are presented. Stellar evolution calculations are combined with mass loss, model atmospheres with line blanketing, and a spectral type calibration to compute observable parameters of massive stars as a function of the star formation rate and the initial mass function slope. The number of O stars of given spectral types, the number of W-R stars, supernova rates, and fluxes of ionizing photons are predicted. Important constraints for the theories of stellar atmospheres and stellar evolution can be derived from observations if stellar number counts and ionizing flux data are available. 94 refs

Massive stars in colliding wind systems: the GLAST perspective

International Nuclear Information System (INIS)

Reimer, Anita; Reimer, Olaf

2007-01-01

Colliding winds of massive stars in binary systems arc considered as candidate sites of high-energy non-thermal photon emission. They are already among the suggested counterparts for a few individual unidentified EGRET sources, but may constitute a detectable source population for the GLAST observatory.The present work investigates such population study of massive colliding wind systems at high-energy gamma-rays. Based on the recent detailed model (Reimer et al. 2006) for non-thermal photon production in prime candidate systems, we unveil the expected characteristics of this source class in the observables accessible at LAT energies. Combining the broadband emission model with the presently cataloged distribution of such systems and their individual parameters allows us to conclude on the expected maximum number of LAT-detections among massive stars in colliding wind binary systems

Late stages of massive star evolution and nucleosynthesis

International Nuclear Information System (INIS)

Nomoto, Ken'ichi; Hashimoto, Masa-aki.

1986-01-01

The evolution of massive stars in the mass range of 8 to 25 M solar mass is reviewed. The effect of electron degeneracy on the gravothermal nature of stars is discussed. Depending on the stellar mass, the stars form three types of cores, namely, non-degenerate, semi-degenerate, and strongly degenerate cores. The evolution for these cases is quite distinct from each other and leads to the three different types of final fate. It is suggested that our helium star model, which is equivalent to a 25 M solar mass star, will form a relatively small mass iron core despite the faster 12 C(α,γ) 16 O reaction. 50 refs., 21 figs

VERY LOW MASS STELLAR AND SUBSTELLAR COMPANIONS TO SOLAR-LIKE STARS FROM MARVELS. I. A LOW-MASS RATIO STELLAR COMPANION TO TYC 4110-01037-1 IN A 79 DAY ORBIT

International Nuclear Information System (INIS)

Wisniewski, John P.; Agol, Eric; Barnes, Rory; Ge, Jian; De Lee, Nathan; Fleming, Scott W.; Lee, Brian L.; Chang, Liang; Crepp, Justin R.; Eastman, Jason; Gaudi, B. Scott; Esposito, Massimiliano; Gonzalez Hernandez, Jonay I.; Prieto, Carlos Allende; Ghezzi, Luan; Da Costa, Luiz N.; Porto De Mello, G. F.; Stassun, Keivan G.; Cargile, Phillip; Bizyaev, Dmitry

2012-01-01

TYC 4110-01037-1 has a low-mass stellar companion, whose small mass ratio and short orbital period are atypical among binary systems with solar-like (T eff ∼ ☉ and radius of 0.99 ± 0.18 R ☉ . We analyze 32 radial velocity (RV) measurements from the SDSS-III MARVELS survey as well as 6 supporting RV measurements from the SARG spectrograph on the 3.6 m Telescopio Nazionale Galileo telescope obtained over a period of ∼2 years. The best Keplerian orbital fit parameters were found to have a period of 78.994 ± 0.012 days, an eccentricity of 0.1095 ± 0.0023, and a semi-amplitude of 4199 ± 11 m s –1 . We determine the minimum companion mass (if sin i = 1) to be 97.7 ± 5.8 M Jup . The system's companion to host star mass ratio, ≥0.087 ± 0.003, places it at the lowest end of observed values for short period stellar companions to solar-like (T eff ∼< 6000 K) stars. One possible way to create such a system would be if a triple-component stellar multiple broke up into a short period, low q binary during the cluster dispersal phase of its lifetime. A candidate tertiary body has been identified in the system via single-epoch, high contrast imagery. If this object is confirmed to be comoving, we estimate it would be a dM4 star. We present these results in the context of our larger-scale effort to constrain the statistics of low-mass stellar and brown dwarf companions to FGK-type stars via the MARVELS survey.

Wide-Field Infrared Survey Explorer Observations of the Evolution of Massive Star-Forming Regions

Science.gov (United States)

Koenig, X. P.; Leisawitz, D. T.; Benford, D. J.; Rebull, L. M.; Padgett, D. L.; Asslef, R. J.

2012-01-01

We present the results of a mid-infrared survey of II outer Galaxy massive star-forming regions and 3 open clusters with data from the Wide-field Infrared Survey Explorer (WISE). Using a newly developed photometric scheme to identify young stellar objects and exclude extragalactic contamination, we have studied the distribution of young stars within each region. These data tend to support the hypothesis that latter generations may be triggered by the interaction of winds and radiation from the first burst of massive star formation with the molecular cloud material leftover from that earlier generation of stars. We dub this process the "fireworks hypothesis" since star formation by this mechanism would proceed rapidly and resemble a burst of fireworks. We have also analyzed small cutout WISE images of the structures around the edges of these massive star-forming regions. We observe large (1-3 pc size) pillar and trunk-like structures of diffuse emission nebulosity tracing excited polycyclic aromatic hydrocarbon molecules and small dust grains at the perimeter of the massive star-forming regions. These structures contain small clusters of emerging Class I and Class II sources, but some are forming only a single to a few new stars.

WIDE-FIELD INFRARED SURVEY EXPLORER OBSERVATIONS OF THE EVOLUTION OF MASSIVE STAR-FORMING REGIONS

International Nuclear Information System (INIS)

Koenig, X. P.; Leisawitz, D. T.; Benford, D. J.; Padgett, D. L.; Rebull, L. M.; Assef, R. J.

2012-01-01

We present the results of a mid-infrared survey of 11 outer Galaxy massive star-forming regions and 3 open clusters with data from the Wide-field Infrared Survey Explorer (WISE). Using a newly developed photometric scheme to identify young stellar objects and exclude extragalactic contamination, we have studied the distribution of young stars within each region. These data tend to support the hypothesis that latter generations may be triggered by the interaction of winds and radiation from the first burst of massive star formation with the molecular cloud material leftover from that earlier generation of stars. We dub this process the 'fireworks hypothesis' since star formation by this mechanism would proceed rapidly and resemble a burst of fireworks. We have also analyzed small cutout WISE images of the structures around the edges of these massive star-forming regions. We observe large (1-3 pc size) pillar and trunk-like structures of diffuse emission nebulosity tracing excited polycyclic aromatic hydrocarbon molecules and small dust grains at the perimeter of the massive star-forming regions. These structures contain small clusters of emerging Class I and Class II sources, but some are forming only a single to a few new stars.

The formation of massive molecular filaments and massive stars triggered by a magnetohydrodynamic shock wave

Science.gov (United States)

Inoue, Tsuyoshi; Hennebelle, Patrick; Fukui, Yasuo; Matsumoto, Tomoaki; Iwasaki, Kazunari; Inutsuka, Shu-ichiro

2018-05-01

Recent observations suggest an that intensive molecular cloud collision can trigger massive star/cluster formation. The most important physical process caused by the collision is a shock compression. In this paper, the influence of a shock wave on the evolution of a molecular cloud is studied numerically by using isothermal magnetohydrodynamics simulations with the effect of self-gravity. Adaptive mesh refinement and sink particle techniques are used to follow the long-time evolution of the shocked cloud. We find that the shock compression of a turbulent inhomogeneous molecular cloud creates massive filaments, which lie perpendicularly to the background magnetic field, as we have pointed out in a previous paper. The massive filament shows global collapse along the filament, which feeds a sink particle located at the collapse center. We observe a high accretion rate \\dot{M}_acc> 10^{-4} M_{⊙}yr-1 that is high enough to allow the formation of even O-type stars. The most massive sink particle achieves M > 50 M_{⊙} in a few times 105 yr after the onset of the filament collapse.

Gravitational waves from remnant massive neutron stars of binary neutron star merger: Viscous hydrodynamics effects

Science.gov (United States)

Shibata, Masaru; Kiuchi, Kenta

2017-06-01

Employing a simplified version of the Israel-Stewart formalism of general-relativistic shear-viscous hydrodynamics, we explore the evolution of a remnant massive neutron star of binary neutron star merger and pay special attention to the resulting gravitational waveforms. We find that for the plausible values of the so-called viscous alpha parameter of the order 10-2 the degree of the differential rotation in the remnant massive neutron star is significantly reduced in the viscous time scale, ≲5 ms . Associated with this, the degree of nonaxisymmetric deformation is also reduced quickly, and as a consequence, the amplitude of quasiperiodic gravitational waves emitted also decays in the viscous time scale. Our results indicate that for modeling the evolution of the merger remnants of binary neutron stars we would have to take into account magnetohydrodynamics effects, which in nature could provide the viscous effects.

A CATALOG OF NEW SPECTROSCOPICALLY CONFIRMED MASSIVE OB STARS IN CARINA

Energy Technology Data Exchange (ETDEWEB)

Alexander, Michael J.; Hanes, Richard J.; McSwain, M. Virginia [Department of Physics, Lehigh University, 16 Memorial Drive East, Bethlehem, PA 18015 (United States); Povich, Matthew S., E-mail: alexamic@lafayette.edu, E-mail: rjh314@lehigh.edu, E-mail: mcswain@lehigh.edu, E-mail: mspovich@cpp.edu [Department of Physics and Astronomy, California State Polytechnic University, Pomona, CA 91768 (United States)

2016-12-01

The Carina star-forming region is one of the largest in the Galaxy, and its massive star population is still being unveiled. The large number of stars combined with high, and highly variable, interstellar extinction makes it inherently difficult to find OB stars in this type of young region. We present the results of a spectroscopic campaign to study the massive star population of the Carina Nebula, with the primary goal to confirm or reject previously identified Carina OB star candidates. A total of 141 known O- and B-type stars and 94 candidates were observed, of which 73 candidates had high enough signal-to-noise ratio to classify. We find 23 new OB stars within the Carina Nebula, a 32% confirmation rate. One of the new OB stars has blended spectra and is suspected to be a double-lined spectroscopic binary (SB2). We also reclassify the spectral types of the known OB stars and discover nine new SB2s among this population. Finally, we discuss the spatial distribution of these new OB stars relative to known structures in the Carina Nebula.

Molecular line study of massive star-forming regions from the Red MSX Source survey

Science.gov (United States)

Yu, Naiping; Wang, Jun-Jie

2014-05-01

In this paper, we have selected a sample of massive star-forming regions from the Red MSX Source survey, in order to study star formation activities (mainly outflow and inflow signatures). We have focused on three molecular lines from the Millimeter Astronomy Legacy Team Survey at 90 GHz: HCO+(1-0), H13CO+(1-0) and SiO(2-1). According to previous observations, our sources can be divided into two groups: nine massive young stellar object candidates (radio-quiet) and 10 H II regions (which have spherical or unresolved radio emissions). Outflow activities have been found in 11 sources, while only three show inflow signatures in all. The high outflow detection rate means that outflows are common in massive star-forming regions. The inflow detection rate was relatively low. We suggest that this was because of the beam dilution of the telescope. All three inflow candidates have outflow(s). The outward radiation and thermal pressure from the central massive star(s) do not seem to be strong enough to halt accretion in G345.0034-00.2240. Our simple model of G318.9480-00.1969 shows that it has an infall velocity of about 1.8 km s-1. The spectral energy distribution analysis agrees our sources are massive and intermediate-massive star formation regions.

Hot stars in young massive clusters: Mapping the current Galactic metallicity

Science.gov (United States)

de la Fuente, Diego; Najarro, Francisco; Davies, Ben; Trombley, Christine; Figer, Donald F.; Herrero, Artemio

2013-06-01

Young Massive Clusters (YMCs) with ages guarantee that these objects present the same chemical composition than the surrounding environment where they are recently born. Finally, the YMCs host very massive stars whose extreme luminosities allow to accomplish detailed spectroscopic analyses even in the most distant regions of the Milky Way. Our group has carried out ISAAC/VLT spectroscopic observations of hot massive stars belonging to several YMCs in different locations around the Galactic disk. As a result, high signal-to-noise, near-infrared spectra of dozens of blue massive stars (including many OB supergiants, Wolf-Rayet stars and a B hypergiant) have been obtained. These data are fully reduced, and NLTE spherical atmosphere modeling is in process. Several line diagnostics will be combined in order to calculate metal abundances accurately for each cluster. The diverse locations of the clusters will allow us to draw a two-dimensional chemical map of the Galactic disk for the first time. The study of the radial and azimuthal variations of elemental abundances will be crucial for understanding the chemical evolution of the Milky Way. Particularly, the ratio between Fe-peak and alpha elements will constitute a powerful tool to investigate the past stellar populations that originated the current Galactic chemistry.

KMOS"3"D Reveals Low-level Star Formation Activity in Massive Quiescent Galaxies at 0.7 < z < 2.7

International Nuclear Information System (INIS)

Belli, Sirio; Genzel, Reinhard; Förster Schreiber, Natascha M.; Wisnioski, Emily; Wilman, David J.; Mendel, J. Trevor; Beifiori, Alessandra; Bender, Ralf; Burkert, Andreas; Chan, Jeffrey; Davies, Rebecca L.; Davies, Ric; Fabricius, Maximilian; Fossati, Matteo; Galametz, Audrey; Lang, Philipp; Lutz, Dieter; Wuyts, Stijn; Brammer, Gabriel B.; Momcheva, Ivelina G.

2017-01-01

We explore the H α emission in the massive quiescent galaxies observed by the KMOS"3"D survey at 0.7 < z < 2.7. The H α line is robustly detected in 20 out of 120 UVJ -selected quiescent galaxies, and we classify the emission mechanism using the H α line width and the [N ii]/H α line ratio. We find that AGNs are likely to be responsible for the line emission in more than half of the cases. We also find robust evidence for star formation activity in nine quiescent galaxies, which we explore in detail. The H α kinematics reveal rotating disks in five of the nine galaxies. The dust-corrected H α star formation rates are low (0.2–7 M _⊙ yr"−"1), and place these systems significantly below the main sequence. The 24 μ m-based, infrared luminosities, instead, overestimate the star formation rates. These galaxies present a lower gas-phase metallicity compared to star-forming objects with similar stellar mass, and many of them have close companions. We therefore conclude that the low-level star formation activity in these nine quiescent galaxies is likely to be fueled by inflowing gas or minor mergers, and could be a sign of rejuvenation events.

Formation of the First Star Clusters and Massive Star Binaries by Fragmentation of Filamentary Primordial Gas Clouds

Science.gov (United States)

Hirano, Shingo; Yoshida, Naoki; Sakurai, Yuya; Fujii, Michiko S.

2018-03-01

We perform a set of cosmological simulations of early structure formation incorporating baryonic streaming motions. We present a case where a significantly elongated gas cloud with ∼104 solar mass (M ⊙) is formed in a pre-galactic (∼107 M ⊙) dark halo. The gas streaming into the halo compresses and heats the massive filamentary cloud to a temperature of ∼10,000 Kelvin. The gas cloud cools rapidly by atomic hydrogen cooling, and then by molecular hydrogen cooling down to ∼400 Kelvin. The rapid decrease of the temperature and hence of the Jeans mass triggers fragmentation of the filament to yield multiple gas clumps with a few hundred solar masses. We estimate the mass of the primordial star formed in each fragment by adopting an analytic model based on a large set of radiation hydrodynamics simulations of protostellar evolution. The resulting stellar masses are in the range of ∼50–120 M ⊙. The massive stars gravitationally attract each other and form a compact star cluster. We follow the dynamics of the star cluster using a hybrid N-body simulation. We show that massive star binaries are formed in a few million years through multi-body interactions at the cluster center. The eventual formation of the remnant black holes will leave a massive black hole binary, which can be a progenitor of strong gravitational wave sources similar to those recently detected by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO).

The role of rotation in the evolution of massive stars losing mass

International Nuclear Information System (INIS)

Sreenivasan, S.R.; Wilson, W.J.F.

1979-01-01

The role of differential and solid body rotation in the evolution of massive stars undergoing mass loss is discussed. The implications for Of, WR, β Cephei stars and shell stars are brought out. (Auth.)

KELT-19Ab: A P ∼ 4.6-day Hot Jupiter Transiting a Likely Am Star with a Distant Stellar Companion

Science.gov (United States)

Siverd, Robert J.; Collins, Karen A.; Zhou, George; Quinn, Samuel N.; Gaudi, B. Scott; Stassun, Keivan G.; Johnson, Marshall C.; Bieryla, Allyson; Latham, David W.; Ciardi, David R.; Rodriguez, Joseph E.; Penev, Kaloyan; Pinsonneault, Marc; Pepper, Joshua; Eastman, Jason D.; Relles, Howard; Kielkopf, John F.; Gregorio, Joao; Oberst, Thomas E.; Aldi, Giulio Francesco; Esquerdo, Gilbert A.; Calkins, Michael L.; Berlind, Perry; Dressing, Courtney D.; Patel, Rahul; Stevens, Daniel J.; Beatty, Thomas G.; Lund, Michael B.; Labadie-Bartz, Jonathan; Kuhn, Rudolf B.; Colón, Knicole D.; James, David; Yao, Xinyu; Johnson, John A.; Wright, Jason T.; McCrady, Nate; Wittenmyer, Robert A.; Johnson, Samson A.; Sliski, David H.; Jensen, Eric L. N.; Cohen, David H.; McLeod, Kim K.; Penny, Matthew T.; Joner, Michael D.; Stephens, Denise C.; Villanueva, Steven, Jr.; Zambelli, Roberto; Stockdale, Christopher; Evans, Phil; Tan, Thiam-Guan; Curtis, Ivan A.; Reed, Phillip A.; Trueblood, Mark; Trueblood, Patricia

2018-01-01

We present the discovery of the giant planet KELT-19Ab, which transits the moderately bright (V∼ 9.9) A8V star TYC 764-1494-1 with an orbital period of 4.61 days. We confirm the planetary nature of the companion via a combination of radial velocities, which limit the mass to ≲ 4.1 {M}{{J}} (3σ ), and a clear Doppler tomography signal, which indicates a retrograde projected spin–orbit misalignment of λ =-{179.7}-3.8+3.7 degrees. Global modeling indicates that the {T}{eff}=7500+/- 110 K host star has {M}\\star ={1.62}-0.20+0.25 {M}ȯ and {R}\\star =1.83+/- 0.10 {R}ȯ . The planet has a radius of {R}P=1.91+/- 0.11 {R}{{J}} and receives a stellar insolation flux of ∼ 3.2× {10}9 {erg} {{{s}}}-1 {{cm}}-2, leading to an inferred equilibrium temperature of {T}{eq}∼ 1935 K assuming zero albedo and complete heat redistribution. With a v\\sin {I}* =84.8+/- 2.0 {km} {{{s}}}-1, the host is relatively slowly rotating compared to other stars with similar effective temperatures, and it appears to be enhanced in metallic elements but deficient in calcium, suggesting that it is likely an Am star. KELT-19A would be the first detection of an Am host of a transiting planet of which we are aware. Adaptive optics observations of the system reveal the existence of a companion with late-G9V/early-K1V spectral type at a projected separation of ≈ 160 {au}. Radial velocity measurements indicate that this companion is bound. Most Am stars are known to have stellar companions, which are often invoked to explain the relatively slow rotation of the primary. In this case, the stellar companion is unlikely to have caused the tidal braking of the primary. However, it may have emplaced the transiting planetary companion via the Kozai–Lidov mechanism.

Effects of a new 3-alpha reaction on the s-process in massive stars

International Nuclear Information System (INIS)

Kikuch, Yukihiro; Ono, Masaomi; Matsuo, Yasuhide; Hashimoto, Masa-aki; Fujimoto, Shin-ichiro

2012-01-01

Effect of a new 3-alpha reaction rate on the s-process during the evolution of a massive star of 25 solar mass is investigated for the first time, because the s-process in massive stars have been believed to be established with only minor change. We find that the s-process with use of the new rate during the core helium burning is very inefficient compared to the case with the previous 3-alpha rate. However, the difference of the overproduction is found to be largely compensated by the subsequent carbon burning. Since the s-process in massive stars has been attributed so far to the neutron irradiation during core helium burning, our finding reveals for the first time the importance of the carbon burning for the s-process during the evolution of massive stars.

PLANETS AROUND LOW-MASS STARS (PALMS). V. AGE-DATING LOW-MASS COMPANIONS TO MEMBERS AND INTERLOPERS OF YOUNG MOVING GROUPS

Energy Technology Data Exchange (ETDEWEB)

Bowler, Brendan P.; Montet, Benjamin T.; Riddle, Reed [California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125 (United States); Shkolnik, Evgenya L.; Flagg, Laura [Lowell Observatory, 1400 W. Mars Hill Road, Flagstaff, AZ 86001 (United States); Liu, Michael C.; Howard, Andrew W.; Aller, Kimberly M.; Best, William M. J.; Kotson, Michael C.; Baranec, Christoph [Institute for Astronomy, University of Hawai‘i at Mānoa, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Schlieder, Joshua E. [NASA Postdoctoral Program Fellow, NASA Ames Research Center, MS-245-3, Moffett Field, CA 94035 (United States); Mann, Andrew W.; Dupuy, Trent J. [Department of Astronomy, University of Texas at Austin, TX (United States); Hinkley, Sasha [Physics and Astronomy, University of Exeter, EX4 4QL Exeter (United Kingdom); Crepp, Justin R. [Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Johnson, John Asher [Harvard–Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Weinberger, Alycia J. [Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Rd NW, Washington, DC 20015 (United States); Allers, Katelyn N. [Department of Physics and Astronomy, Bucknell University, Lewisburg, PA 17837 (United States); Herczeg, Gregory J., E-mail: bpbowler@caltech.edu [Kavli Institute for Astronomy and Astrophysics, Peking University, Yi He Yuan Lu 5, Hai Dian Qu, Beijing 100871 (China); and others

2015-06-10

We present optical and near-infrared adaptive optics (AO) imaging and spectroscopy of 13 ultracool (>M6) companions to late-type stars (K7–M4.5), most of which have recently been identified as candidate members of nearby young moving groups (YMGs; 8–120 Myr) in the literature. Three of these are new companions identified in our AO imaging survey, and two others are confirmed to be comoving with their host stars for the first time. The inferred masses of the companions (∼10–100 M{sub Jup}) are highly sensitive to the ages of the primary stars; therefore we critically examine the kinematic and spectroscopic properties of each system to distinguish bona fide YMG members from old field interlopers. The new M7 substellar companion 2MASS J02155892–0929121 C (40–60 M{sub Jup}) shows clear spectroscopic signs of low gravity and, hence, youth. The primary, possibly a member of the ∼40 Myr Tuc-Hor moving group, is visually resolved into three components, making it a young low-mass quadruple system in a compact (≲100 AU) configuration. In addition, Li i λ6708 absorption in the intermediate-gravity M7.5 companion 2MASS J15594729+4403595 B provides unambiguous evidence that it is young (≲200 Myr) and resides below the hydrogen-burning limit. Three new close-separation (<1″) companions (2MASS J06475229–2523304 B, PYC J11519+0731 B, and GJ 4378 Ab) orbit stars previously reported as candidate YMG members, but instead are likely old (≳1 Gyr) tidally locked spectroscopic binaries without convincing kinematic associations with any known moving group. The high rate of false positives in the form of old active stars with YMG-like kinematics underscores the importance of radial velocity and parallax measurements to validate candidate young stars identified via proper motion and activity selection alone. Finally, we spectroscopically confirm the cool temperature and substellar nature of HD 23514 B, a recently discovered M8 benchmark brown dwarf orbiting the

PLANETS AROUND LOW-MASS STARS (PALMS). V. AGE-DATING LOW-MASS COMPANIONS TO MEMBERS AND INTERLOPERS OF YOUNG MOVING GROUPS

International Nuclear Information System (INIS)

Bowler, Brendan P.; Montet, Benjamin T.; Riddle, Reed; Shkolnik, Evgenya L.; Flagg, Laura; Liu, Michael C.; Howard, Andrew W.; Aller, Kimberly M.; Best, William M. J.; Kotson, Michael C.; Baranec, Christoph; Schlieder, Joshua E.; Mann, Andrew W.; Dupuy, Trent J.; Hinkley, Sasha; Crepp, Justin R.; Johnson, John Asher; Weinberger, Alycia J.; Allers, Katelyn N.; Herczeg, Gregory J.

2015-01-01

We present optical and near-infrared adaptive optics (AO) imaging and spectroscopy of 13 ultracool (>M6) companions to late-type stars (K7–M4.5), most of which have recently been identified as candidate members of nearby young moving groups (YMGs; 8–120 Myr) in the literature. Three of these are new companions identified in our AO imaging survey, and two others are confirmed to be comoving with their host stars for the first time. The inferred masses of the companions (∼10–100 M Jup ) are highly sensitive to the ages of the primary stars; therefore we critically examine the kinematic and spectroscopic properties of each system to distinguish bona fide YMG members from old field interlopers. The new M7 substellar companion 2MASS J02155892–0929121 C (40–60 M Jup ) shows clear spectroscopic signs of low gravity and, hence, youth. The primary, possibly a member of the ∼40 Myr Tuc-Hor moving group, is visually resolved into three components, making it a young low-mass quadruple system in a compact (≲100 AU) configuration. In addition, Li i λ6708 absorption in the intermediate-gravity M7.5 companion 2MASS J15594729+4403595 B provides unambiguous evidence that it is young (≲200 Myr) and resides below the hydrogen-burning limit. Three new close-separation (<1″) companions (2MASS J06475229–2523304 B, PYC J11519+0731 B, and GJ 4378 Ab) orbit stars previously reported as candidate YMG members, but instead are likely old (≳1 Gyr) tidally locked spectroscopic binaries without convincing kinematic associations with any known moving group. The high rate of false positives in the form of old active stars with YMG-like kinematics underscores the importance of radial velocity and parallax measurements to validate candidate young stars identified via proper motion and activity selection alone. Finally, we spectroscopically confirm the cool temperature and substellar nature of HD 23514 B, a recently discovered M8 benchmark brown dwarf orbiting the dustiest

SPECKLE IMAGING EXCLUDES LOW-MASS COMPANIONS ORBITING THE EXOPLANET HOST STAR TRAPPIST-1

International Nuclear Information System (INIS)

Howell, Steve B.; Scott, Nicholas J.; Everett, Mark E.; Horch, Elliott P.; Winters, Jennifer G.; Hirsch, Lea; Nusdeo, Dan

2016-01-01

We have obtained the highest-resolution images available of TRAPPIST-1 using the Gemini-South telescope and our speckle imaging camera. Observing at 692 and 883 nm, we reached the diffraction limit of the telescope providing a best resolution of 27 mas or, at the distance of TRAPPIST-1, a spatial resolution of 0.32 au. Our imaging of the star extends from 0.32 to 14.5 au. We show that to a high confidence level, we can exclude all possible stellar and brown dwarf companions, indicating that TRAPPIST-1 is a single star.

SPECKLE IMAGING EXCLUDES LOW-MASS COMPANIONS ORBITING THE EXOPLANET HOST STAR TRAPPIST-1

Energy Technology Data Exchange (ETDEWEB)

Howell, Steve B.; Scott, Nicholas J. [NASA Ames Research Center, Moffett Field, CA 94035 (United States); Everett, Mark E. [National Optical Astronomy Observatory, 950 N. Cherry Avenue, Tucson, AZ 85719 (United States); Horch, Elliott P. [Department of Physics, Southern Connecticut State University, 501 Crescent Street, New Haven, CT, 06515 (United States); Winters, Jennifer G. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, 02138 (United States); Hirsch, Lea [Astronomy Department, University of California, Berkeley, 510 Campbell Hall, Berkeley, CA, 94720 (United States); Nusdeo, Dan [Department of Physics and Astronomy, Georgia State University, P.O. Box 5060, Atlanta, GA 30302 (United States)

2016-09-20

We have obtained the highest-resolution images available of TRAPPIST-1 using the Gemini-South telescope and our speckle imaging camera. Observing at 692 and 883 nm, we reached the diffraction limit of the telescope providing a best resolution of 27 mas or, at the distance of TRAPPIST-1, a spatial resolution of 0.32 au. Our imaging of the star extends from 0.32 to 14.5 au. We show that to a high confidence level, we can exclude all possible stellar and brown dwarf companions, indicating that TRAPPIST-1 is a single star.

VERY LOW MASS STELLAR AND SUBSTELLAR COMPANIONS TO SOLAR-LIKE STARS FROM MARVELS. IV. A CANDIDATE BROWN DWARF OR LOW-MASS STELLAR COMPANION TO HIP 67526

Energy Technology Data Exchange (ETDEWEB)

Jiang Peng; Ge Jian; De Lee, Nathan; Fleming, Scott W.; Lee, Brian L.; Ma Bo; Wang, Ji [Astronomy Department, University of Florida, 211 Bryant Space Science Center, P.O. Box 112055, Gainesville, FL 32611 (United States); Cargile, Phillip; Hebb, Leslie; Stassun, Keivan G. [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States); Crepp, Justin R. [Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Porto de Mello, Gustavo F.; Ferreira, Leticia D. [Observatorio do Valongo, Universidade Federal do Rio de Janeiro, Ladeira do Pedro Antonio, 43, CEP: 20080-090, Rio de Janeiro, RJ (Brazil); Esposito, Massimiliano; Femenia, Bruno; Gonzalez Hernandez, Jonay I. [Instituto de Astrofisica de Canarias, C/Via Lactea S/N, E-38200 La Laguna (Spain); Gaudi, B. Scott [Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States); Ghezzi, Luan [Laboratorio Interinstitucional de e-Astronomia (LIneA), Rio de Janeiro, RJ 20921-400 (Brazil); Wisniewski, John P. [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 West Brooks Street, Norman, OK 73019 (United States); Agol, Eric, E-mail: jpaty@mail.ustc.edu.cn [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195-1580 (United States); and others

2013-09-15

We report the discovery of a candidate brown dwarf (BD) or a very low mass stellar companion (MARVELS-5b) to the star HIP 67526 from the Multi-object Apache point observatory Radial Velocity Exoplanet Large-area Survey (MARVELS). The radial velocity curve for this object contains 31 epochs spread over 2.5 yr. Our Keplerian fit, using a Markov Chain Monte Carlo approach, reveals that the companion has an orbital period of 90.2695{sup +0.0188}{sub -0.0187} days, an eccentricity of 0.4375 {+-} 0.0040, and a semi-amplitude of 2948.14{sup +16.65}{sub -16.55} m s{sup -1}. Using additional high-resolution spectroscopy, we find the host star has an effective temperature T{sub eff} = 6004 {+-} 34 K, a surface gravity log g (cgs) =4.55 {+-} 0.17, and a metallicity [Fe/H] =+0.04 {+-} 0.06. The stellar mass and radius determined through the empirical relationship of Torres et al. yields 1.10 {+-} 0.09 M{sub Sun} and 0.92 {+-} 0.19 R{sub Sun }. The minimum mass of MARVELS-5b is 65.0 {+-} 2.9M{sub Jup}, indicating that it is likely to be either a BD or a very low mass star, thus occupying a relatively sparsely populated region of the mass function of companions to solar-type stars. The distance to this system is 101 {+-} 10 pc from the astrometric measurements of Hipparcos. No stellar tertiary is detected in the high-contrast images taken by either FastCam lucky imaging or Keck adaptive optics imaging, ruling out any star with mass greater than 0.2 M{sub Sun} at a separation larger than 40 AU.

Curtain-Lifting Winds Allow Rare Glimpse into Massive Star Factory

Science.gov (United States)

2003-06-01

Formation of Exceedingly Luminous and Hot Stars in Young Stellar Cluster Observed Directly Summary Based on a vast observational effort with different telescopes and instruments, ESO-astronomer Dieter Nürnberger has obtained a first glimpse of the very first stages in the formation of heavy stars. These critical phases of stellar evolution are normally hidden from the view, because massive protostars are deeply embedded in their native clouds of dust and gas, impenetrable barriers to observations at all but the longest wavelengths. In particular, no visual or infrared observations have yet "caught" nascent heavy stars in the act and little is therefore known so far about the related processes. Profiting from the cloud-ripping effect of strong stellar winds from adjacent, hot stars in a young stellar cluster at the center of the NGC 3603 complex, several objects located near a giant molecular cloud were found to be bona-fide massive protostars, only about 100,000 years old and still growing. Three of these objects, designated IRS 9A-C, could be studied in more detail. They are very luminous (IRS 9A is about 100,000 times intrinsically brighter than the Sun), massive (more than 10 times the mass of the Sun) and hot (about 20,000 degrees). They are surrounded by relative cold dust (about 0°C), probably partly arranged in disks around these very young objects. Two possible scenarios for the formation of massive stars are currently proposed, by accretion of large amounts of circumstellar material or by collision (coalescence) of protostars of intermediate masses. The new observations favour accretion, i.e. the same process that is active during the formation of stars of smaller masses. PR Photo 16a/03: Stellar cluster and star-forming region NGC 3603. PR Photo 16b/03: Region near very young, massive stars IRS 9A-C in NGC 3603 (8 bands from J to Q). How do massive stars form? This question is easy to pose, but so far very difficult to answer. In fact, the processes

CLOSE COMPANIONS TO YOUNG STARS. I. A LARGE SPECTROSCOPIC SURVEY IN CHAMAELEON I AND TAURUS-AURIGA

International Nuclear Information System (INIS)

Nguyen, Duy Cuong; Brandeker, Alexis; Van Kerkwijk, Marten H.; Jayawardhana, Ray

2012-01-01

We present the results of a multiplicity survey of 212 T Tauri stars in the Chamaeleon I and Taurus-Auriga star-forming regions, based on high-resolution spectra from the Magellan Clay 6.5 m telescope. From these data, we achieved a typical radial velocity (RV) precision of ∼80 m s –1 with slower rotators yielding better precision, in general. For 174 of these stars, we obtained multi-epoch data with sufficient time baselines to identify binaries based on RV variations. We identified eight close binaries and four close triples, of which three and two, respectively, are new discoveries. The spectroscopic multiplicity fractions we find for Chamaeleon I (7%) and Taurus-Auriga (6%) are similar to each other, and to the results of field star surveys in the same mass and period regime. However, unlike the results from imaging surveys, the frequency of systems with close companions in our sample is not seen to depend on primary mass. Additionally, we do not find a strong correlation between accretion and close multiplicity. This implies that close companions are not likely the main source of the accretion shut down observed in weak-lined T Tauri stars. Our results also suggest that sufficient RV precision can be achieved for at least a subset of slowly rotating young stars to search for hot Jupiter planets.

KMOS{sup 3D} Reveals Low-level Star Formation Activity in Massive Quiescent Galaxies at 0.7 < z < 2.7

Energy Technology Data Exchange (ETDEWEB)

Belli, Sirio; Genzel, Reinhard; Förster Schreiber, Natascha M.; Wisnioski, Emily; Wilman, David J.; Mendel, J. Trevor; Beifiori, Alessandra; Bender, Ralf; Burkert, Andreas; Chan, Jeffrey; Davies, Rebecca L.; Davies, Ric; Fabricius, Maximilian; Fossati, Matteo; Galametz, Audrey; Lang, Philipp; Lutz, Dieter [Max-Planck-Institut für Extraterrestrische Physik (MPE), Giessenbachstr. 1, D-85748 Garching (Germany); Wuyts, Stijn [Department of Physics, University of Bath, Claverton Down, Bath, BA2 7AY (United Kingdom); Brammer, Gabriel B.; Momcheva, Ivelina G. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); and others

2017-05-20

We explore the H α emission in the massive quiescent galaxies observed by the KMOS{sup 3D} survey at 0.7 < z < 2.7. The H α line is robustly detected in 20 out of 120 UVJ -selected quiescent galaxies, and we classify the emission mechanism using the H α line width and the [N ii]/H α line ratio. We find that AGNs are likely to be responsible for the line emission in more than half of the cases. We also find robust evidence for star formation activity in nine quiescent galaxies, which we explore in detail. The H α kinematics reveal rotating disks in five of the nine galaxies. The dust-corrected H α star formation rates are low (0.2–7 M {sub ⊙} yr{sup −1}), and place these systems significantly below the main sequence. The 24 μ m-based, infrared luminosities, instead, overestimate the star formation rates. These galaxies present a lower gas-phase metallicity compared to star-forming objects with similar stellar mass, and many of them have close companions. We therefore conclude that the low-level star formation activity in these nine quiescent galaxies is likely to be fueled by inflowing gas or minor mergers, and could be a sign of rejuvenation events.

A dearth of short-period massive binaries in the young massive star forming region M 17. Evidence for a large orbital separation at birth?

Science.gov (United States)

Sana, H.; Ramírez-Tannus, M. C.; de Koter, A.; Kaper, L.; Tramper, F.; Bik, A.

2017-03-01

Aims: The formation of massive stars remains poorly understood and little is known about their birth multiplicity properties. Here, we aim to quantitatively investigate the strikingly low radial-velocity dispersion measured for a sample of 11 massive pre- and near-main-sequence stars (σ1D= 5.6 ± 0.2 km s-1) in the very young massive star forming region M 17, in order to obtain first constraints on the multiplicity properties of young massive stellar objects. Methods: We compute the radial-velocity dispersion of synthetic populations of massive stars for various multiplicity properties and we compare the obtained σ1D distributions to the observed value. We specifically investigate two scenarios: a low binary fraction and a dearth of short-period binary systems. Results: Simulated populations with low binary fractions () or with truncated period distributions (Pcutoff > 9 months) are able to reproduce the low σ1D observed within their 68%-confidence intervals. Furthermore, parent populations with fbin > 0.42 or Pcutoff < 47 d can be rejected at the 5%-significance level. Both constraints are in stark contrast with the high binary fraction and plethora of short-period systems in few Myr-old, well characterized OB-type populations. To explain the difference in the context of the first scenario would require a variation of the outcome of the massive star formation process. In the context of the second scenario, compact binaries must form later on, and the cut-off period may be related to physical length-scales representative of the bloated pre-main-sequence stellar radii or of their accretion disks. Conclusions: If the obtained constraints for the M 17's massive-star population are representative of the multiplicity properties of massive young stellar objects, our results may provide support to a massive star formation process in which binaries are initially formed at larger separations, then harden or migrate to produce the typical (untruncated) power-law period

Massive stars, successes and challenges

OpenAIRE

Meynet, Georges; Maeder, André; Georgy, Cyril; Ekström, Sylvia; Eggenberger, Patrick; Barblan, Fabio; Song, Han Feng

2017-01-01

We give a brief overview of where we stand with respect to some old and new questions bearing on how massive stars evolve and end their lifetime. We focus on the following key points that are further discussed by other contributions during this conference: convection, mass losses, rotation, magnetic field and multiplicity. For purpose of clarity, each of these processes are discussed on its own but we have to keep in mind that they are all interacting between them offering a large variety of ...

The Formation and Early Evolution of Embedded Massive Star Clusters

Science.gov (United States)

Barnes, Peter

We propose to combine Spitzer, WISE, Herschel, and other archival spacecraft data with an existing ground- and space-based mm-wave to near-IR survey of molecular clouds over a large portion of the Milky Way, in order to systematically study the formation and early evolution of massive stars and star clusters, and provide new observational calibrations for a theoretical paradigm of this key astrophysical problem. Central Objectives: The Galactic Census of High- and Medium-mass Protostars (CHaMP) is a large, unbiased, uniform, and panchromatic survey of massive star and cluster formation and early evolution, covering 20°x6° of the Galactic Plane. Its uniqueness lies in the comprehensive molecular spectroscopy of 303 massive dense clumps, which have also been included in several archival spacecraft surveys. Our objective is a systematic demographic analysis of massive star and cluster formation, one which has not been possible without knowledge of our CHaMP cloud sample, including all clouds with embedded clusters as well as those that have not yet formed massive stars. For proto-clusters deeply embedded within dense molecular clouds, analysis of these space-based data will: 1. Yield a complete census of Young Stellar Objects in each cluster. 2. Allow systematic measurements of embedded cluster properties: spectral energy distributions, luminosity functions, protostellar and disk fractions, and how these vary with cluster mass, age, and density. Combined with other, similarly complete and unbiased infrared and mm data, CHaMP's goals include: 3. A detailed comparison of the embedded stellar populations with their natal dense gas to derive extinction maps, star formation efficiencies and feedback effects, and the kinematics, physics, and chemistry of the gas in and around the clusters. 4. Tying the demographics, age spreads, and timescales of the clusters, based on pre-Main Sequence evolution, to that of the dense gas clumps and Giant Molecular Clouds. 5. A

A BUTTERFLY-SHAPED 'PAPILLON' NEBULA YIELDS SECRETS OF MASSIVE STAR BIRTH

Science.gov (United States)

2002-01-01

A NASA Hubble Space Telescope view of a turbulent cauldron of starbirth, called N159, taking place 170,000 light-years away in our satellite galaxy, the Large Magellanic Cloud (LMC). Torrential stellar winds from hot newborn massive stars within the nebula sculpt ridges, arcs, and filaments in the vast cloud, which is over 150 light-years across. A rare type of compact ionized 'blob' is resolved for the first time to be a butterfly-shaped or 'Papillon' (French for 'butterfly') nebula, buried in the center of the maelstrom of glowing gases and dark dust. The unprecedented details of the structure of the Papillon, itself less than 2 light-years in size (about 2 arcseconds in the sky), are seen in the inset. A possible explanation of this bipolar shape is the outflow of gas from massive stars (over 10 times the mass of our sun) hidden in the central absorption zone. Such stars are so hot that their radiation pressure halts the infall of gas and directs it away from the stars in two opposite directions. Presumably, a dense equatorial disk formed by matter still trying to fall in onto the stars focuses the outstreaming matter into the bipolar directions. This observation is part of a search for young massive stars in the LMC. Rare are the cases where we can see massive stars so early after their birth. The red in this true-color image is from the emission of hydrogen and the yellow from high excitation ionized oxygen. The picture was taken on September 5, 1998 with the Wide Field Planetary Camera 2. The Hubble observations of the Papillon nebula were conducted by the European astronomers Mohammad Heydari-Malayeri (Paris Observatory, France) and co-investigators Michael Rosa (Space Telescope-European Coordinating Facility, European Southern Observatory, Germany), Vassilis Charmandaris (Paris Observatory), Lise Deharveng (Marseille Observatory, France), and Hans Zinnecker (Astrophysical Institute, Potsdam, Germany). Their work is submitted for publication in the European

Magnetic massive stars as progenitors of `heavy' stellar-mass black holes

Science.gov (United States)

Petit, V.; Keszthelyi, Z.; MacInnis, R.; Cohen, D. H.; Townsend, R. H. D.; Wade, G. A.; Thomas, S. L.; Owocki, S. P.; Puls, J.; ud-Doula, A.

2017-04-01

The groundbreaking detection of gravitational waves produced by the inspiralling and coalescence of the black hole (BH) binary GW150914 confirms the existence of 'heavy' stellar-mass BHs with masses >25 M⊙. Initial characterization of the system by Abbott et al. supposes that the formation of BHs with such large masses from the evolution of single massive stars is only feasible if the wind mass-loss rates of the progenitors were greatly reduced relative to the mass-loss rates of massive stars in the Galaxy, concluding that heavy BHs must form in low-metallicity (Z ≲ 0.25-0.5 Z⊙) environments. However, strong surface magnetic fields also provide a powerful mechanism for modifying mass-loss and rotation of massive stars, independent of environmental metallicity. In this paper, we explore the hypothesis that some heavy BHs, with masses >25 M⊙ such as those inferred to compose GW150914, could be the natural end-point of evolution of magnetic massive stars in a solar-metallicity environment. Using the MESA code, we developed a new grid of single, non-rotating, solar-metallicity evolutionary models for initial zero-age main sequence masses from 40 to 80 M⊙ that include, for the first time, the quenching of the mass-loss due to a realistic dipolar surface magnetic field. The new models predict terminal-age main-sequence (TAMS) masses that are significantly greater than those from equivalent non-magnetic models, reducing the total mass lost by a strongly magnetized 80 M⊙ star during its main-sequence evolution by 20 M⊙. This corresponds approximately to the mass-loss reduction expected from an environment with metallicity Z = 1/30 Z⊙.

Globular Cluster Formation at High Density: A Model for Elemental Enrichment with Fast Recycling of Massive-star Debris

Energy Technology Data Exchange (ETDEWEB)

Elmegreen, Bruce G., E-mail: bge@us.ibm.com [IBM Research Division, T.J. Watson Research Center, 1101 Kitchawan Road, Yorktown Heights, NY 10598 (United States)

2017-02-10

The self-enrichment of massive star clusters by p -processed elements is shown to increase significantly with increasing gas density as a result of enhanced star formation rates and stellar scatterings compared to the lifetime of a massive star. Considering the type of cloud core where a globular cluster (GC) might have formed, we follow the evolution and enrichment of the gas and the time dependence of stellar mass. A key assumption is that interactions between massive stars are important at high density, including interactions between massive stars and massive-star binaries that can shred stellar envelopes. Massive-star interactions should also scatter low-mass stars out of the cluster. Reasonable agreement with the observations is obtained for a cloud-core mass of ∼4 × 10{sup 6} M {sub ⊙} and a density of ∼2 × 10{sup 6} cm{sup −3}. The results depend primarily on a few dimensionless parameters, including, most importantly, the ratio of the gas consumption time to the lifetime of a massive star, which has to be low, ∼10%, and the efficiency of scattering low-mass stars per unit dynamical time, which has to be relatively large, such as a few percent. Also for these conditions, the velocity dispersions of embedded GCs should be comparable to the high gas dispersions of galaxies at that time, so that stellar ejection by multistar interactions could cause low-mass stars to leave a dwarf galaxy host altogether. This could solve the problem of missing first-generation stars in the halos of Fornax and WLM.

Molecular Cloud Structures and Massive Star Formation in N159

Science.gov (United States)

Nayak, O.; Meixner, M.; Fukui, Y.; Tachihara, K.; Onishi, T.; Saigo, K.; Tokuda, K.; Harada, R.

2018-02-01

The N159 star-forming region is one of the most massive giant molecular clouds (GMCs) in the Large Magellanic Cloud (LMC). We show the 12CO, 13CO, CS molecular gas lines observed with ALMA in N159 west (N159W) and N159 east (N159E). We relate the structure of the gas clumps to the properties of 24 massive young stellar objects (YSOs) that include 10 newly identified YSOs based on our search. We use dendrogram analysis to identify properties of the molecular clumps, such as flux, mass, linewidth, size, and virial parameter. We relate the YSO properties to the molecular gas properties. We find that the CS gas clumps have a steeper size–linewidth relation than the 12CO or 13CO gas clumps. This larger slope could potentially occur if the CS gas is tracing shocks. The virial parameters of the 13CO gas clumps in N159W and N159E are low (<1). The threshold for massive star formation in N159W is 501 M ⊙ pc‑2, and the threshold for massive star formation in N159E is 794 M ⊙ pc‑2. We find that 13CO is more photodissociated in N159E than N159W. The most massive YSO in N159E has cleared out a molecular gas hole in its vicinity. All the massive YSO candidates in N159E have a more evolved spectral energy distribution type in comparison to the YSO candidates in N159W. These differences lead us to conclude that the giant molecular cloud complex in N159E is more evolved than the giant molecular cloud complex in N159W.

Constraining the Final Fates of Massive Stars by Oxygen and Iron Enrichment History in the Galaxy

Science.gov (United States)

Suzuki, Akihiro; Maeda, Keiichi

2018-01-01

Recent observational studies of core-collapse supernovae suggest that only stars with zero-age main-sequence masses smaller than 16–18 {M}ȯ explode when they are red supergiants, producing Type IIP supernovae. This may imply that more massive stars produce other types of supernovae or they simply collapse to black holes without giving rise to bright supernovae. This failed supernova hypothesis can lead to significantly inefficient oxygen production because oxygen abundantly produced in inner layers of massive stars with zero-age main-sequence masses around 20–30 {M}ȯ might not be ejected into the surrounding interstellar space. We first assume an unspecified population of oxygen injection events related to massive stars and obtain a model-independent constraint on how much oxygen should be released in a single event and how frequently such events should happen. We further carry out one-box galactic chemical enrichment calculations with different mass ranges of massive stars exploding as core-collapse supernovae. Our results suggest that the model assuming that all massive stars with 9–100 {M}ȯ explode as core-collapse supernovae is still most appropriate in explaining the solar abundances of oxygen and iron and their enrichment history in the Galaxy. The oxygen mass in the Galaxy is not explained when assuming that only massive stars with zero-age main-sequence masses in the range of 9–17 {M}ȯ contribute to the galactic oxygen enrichment. This finding implies that a good fraction of stars more massive than 17 {M}ȯ should eject their oxygen layers in either supernova explosions or some other mass-loss processes.

A RAPIDLY EVOLVING REGION IN THE GALACTIC CENTER: WHY S-STARS THERMALIZE AND MORE MASSIVE STARS ARE MISSING

Energy Technology Data Exchange (ETDEWEB)

Chen, Xian; Amaro-Seoane, Pau, E-mail: Xian.Chen@aei.mpg.de, E-mail: Pau.Amaro-Seoane@aei.mpg.de [Max Planck Institut für Gravitationsphysik (Albert-Einstein-Institut), D-14476 Potsdam (Germany)

2014-05-10

The existence of ''S-stars'' within a distance of 1'' from Sgr A* contradicts our understanding of star formation, due to Sgr A* 's forbiddingly violent environment. A suggested possibility is that they form far away and were brought in by some fast dynamical process, since they are young. Nonetheless, all conjectured mechanisms either fail to reproduce their eccentricities—without violating their young age—or cannot explain the problem of {sup i}nverse mass segregation{sup :} the fact that lighter stars (the S-stars) are closer to Sgr A* and more massive ones, Wolf-Rayet (WR) and O-stars, are farther out. In this Letter we propose that the mechanism responsible for both the distribution of the eccentricities and the paucity of massive stars is the Kozai-Lidov-like resonance induced by a sub-parsec disk recently discovered in the Galactic center. Considering that the disk probably extended to a smaller radius in the past, we show that in as short as (a few) 10{sup 6} yr, the stars populating the innermost 1'' region would redistribute in angular-momentum space and recover the observed ''super-thermal'' distribution. Meanwhile, WR and O-stars in the same region intermittently attain ample eccentricities that will lead to their tidal disruptions by the central massive black hole. Our results provide new evidences that Sgr A* was powered several millions years ago by an accretion disk as well as by tidal stellar disruptions.

Massive stars, successes and challenges

Science.gov (United States)

Meynet, Georges; Maeder, André; Georgy, Cyril; Ekström, Sylvia; Eggenberger, Patrick; Barblan, Fabio; Song, Han Feng

2017-11-01

We give a brief overview of where we stand with respect to some old and new questions bearing on how massive stars evolve and end their lifetime. We focus on the following key points that are further discussed by other contributions during this conference: convection, mass losses, rotation, magnetic field and multiplicity. For purpose of clarity, each of these processes are discussed on its own but we have to keep in mind that they are all interacting between them offering a large variety of outputs, some of them still to be discovered.

Radial Velocity Survey of T Tauri Stars in Taurus-Auriga

Science.gov (United States)

Crockett, Christopher; Mahmud, N.; Huerta, M.; Prato, L.; Johns-Krull, C.; Hartigan, P.; Jaffe, D.

2009-01-01

Is the frequency of giant planet companions to young stars similar to that seen around old stars? Is the "brown dwarf desert" a product of how low-mass companion objects form, or of how they evolve? Some models indicate that both giant planets and brown dwarfs should be common at young ages within 3 AU of a primary star, but migration induced by massive disks drive brown dwarfs into the parent stars, leaving behind proportionally more giant planets. Our radial velocity survey of young stars will provide a census of the young giant planet and brown dwarf population in Taurus-Auriga. In this poster we present our progress in quantifying how spurious radial velocity signatures are caused by stellar activity and in developing models to help distinguish between companion induced and spot induced radial velocity variations. Early results stress the importance of complementary observations in both visible light and NIR. We present our technique to determine radial velocities by fitting telluric features and model stellar features to our observed spectra. Finally, we discuss ongoing observations at McDonald Observatory, KPNO, and the IRTF, and several new exoplanet host candidates.

THE MILKY WAY PROJECT: A STATISTICAL STUDY OF MASSIVE STAR FORMATION ASSOCIATED WITH INFRARED BUBBLES

International Nuclear Information System (INIS)

Kendrew, S.; Robitaille, T. P.; Simpson, R.; Lintott, C. J.; Bressert, E.; Povich, M. S.; Sherman, R.; Schawinski, K.; Wolf-Chase, G.

2012-01-01

The Milky Way Project citizen science initiative recently increased the number of known infrared bubbles in the inner Galactic plane by an order of magnitude compared to previous studies. We present a detailed statistical analysis of this data set with the Red MSX Source (RMS) catalog of massive young stellar sources to investigate the association of these bubbles with massive star formation. We particularly address the question of massive triggered star formation near infrared bubbles. We find a strong positional correlation of massive young stellar objects (MYSOs) and H II regions with Milky Way Project bubbles at separations of <2 bubble radii. As bubble sizes increase, a statistically significant overdensity of massive young sources emerges in the region of the bubble rims, possibly indicating the occurrence of triggered star formation. Based on numbers of bubble-associated RMS sources, we find that 67% ± 3% of MYSOs and (ultra-)compact H II regions appear to be associated with a bubble. We estimate that approximately 22% ± 2% of massive young stars may have formed as a result of feedback from expanding H II regions. Using MYSO-bubble correlations, we serendipitously recovered the location of the recently discovered massive cluster Mercer 81, suggesting the potential of such analyses for discovery of heavily extincted distant clusters.

THE MILKY WAY PROJECT: A STATISTICAL STUDY OF MASSIVE STAR FORMATION ASSOCIATED WITH INFRARED BUBBLES

Energy Technology Data Exchange (ETDEWEB)

Kendrew, S.; Robitaille, T. P. [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany); Simpson, R.; Lintott, C. J. [Department of Astrophysics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH (United Kingdom); Bressert, E. [School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom); Povich, M. S. [Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802 (United States); Sherman, R. [Department of Astronomy and Astrophysics, University of Chicago, 5640 S. Ellis Avenue, Chicago, IL 60637 (United States); Schawinski, K. [Yale Center for Astronomy and Astrophysics, Yale University, P.O. Box 208121, New Haven, CT 06520 (United States); Wolf-Chase, G., E-mail: kendrew@mpia.de [Astronomy Department, Adler Planetarium, 1300 S. Lake Shore Drive, Chicago, IL 60605 (United States)

2012-08-10

The Milky Way Project citizen science initiative recently increased the number of known infrared bubbles in the inner Galactic plane by an order of magnitude compared to previous studies. We present a detailed statistical analysis of this data set with the Red MSX Source (RMS) catalog of massive young stellar sources to investigate the association of these bubbles with massive star formation. We particularly address the question of massive triggered star formation near infrared bubbles. We find a strong positional correlation of massive young stellar objects (MYSOs) and H II regions with Milky Way Project bubbles at separations of <2 bubble radii. As bubble sizes increase, a statistically significant overdensity of massive young sources emerges in the region of the bubble rims, possibly indicating the occurrence of triggered star formation. Based on numbers of bubble-associated RMS sources, we find that 67% {+-} 3% of MYSOs and (ultra-)compact H II regions appear to be associated with a bubble. We estimate that approximately 22% {+-} 2% of massive young stars may have formed as a result of feedback from expanding H II regions. Using MYSO-bubble correlations, we serendipitously recovered the location of the recently discovered massive cluster Mercer 81, suggesting the potential of such analyses for discovery of heavily extincted distant clusters.

Multidimensional Simulations of Colliding Outbursts from very Massive Stars

Science.gov (United States)

Chen, Ke-Jung; Woosley, Stan

2015-08-01

Massive stars that end their lives with helium cores in the range of 35 to 65 solar masses are known to produce repeated thermonuclear outbursts due to a recurring pair-instability. In some of these events, solar masses of material are ejected in repeated outbursts of several times 1050 erg each. Such models can be used to explain the strong mass loss rates at the last moment before the massive stars die. Collisions between these shells can sometimes produce very luminous transients. Previous 1D studies of these events produce thin,high-density shells as one ejection plows into another. We present the first multidimensional simulations of these collisions, we show that the development of a Rayleigh-Taylor instability truncates the growth of the high density spike and drives mixing between the shells.

Winds of Massive Magnetic Stars: Interacting Fields and Flow

Science.gov (United States)

Daley-Yates, S.; Stevens, I. R.

2018-01-01

We present results of 3D numerical simulations of magnetically confined, radiatively driven stellar winds of massive stars, conducted using the astrophysical MHD code Pluto, with a focus on understanding the rotational variability of radio and sub-mm emission. Radiative driving is implemented according to the Castor, Abbott and Klein theory of radiatively driven winds. Many magnetic massive stars posses a magnetic axis which is inclined with respect to the rotational axis. This misalignment leads to a complex wind structure as magnetic confinement, centrifugal acceleration and radiative driving act to channel the circumstellar plasma into a warped disk whose observable properties should be apparent in multiple wavelengths. This structure is analysed to calculate free-free thermal radio emission and determine the characteristic intensity maps and radio light curves.

SPITZER VIEW OF YOUNG MASSIVE STARS IN THE LARGE MAGELLANIC CLOUD H II COMPLEXES. II. N 159

International Nuclear Information System (INIS)

Chen, C.-H. Rosie; Indebetouw, Remy; Chu, You-Hua; Gruendl, Robert A.; Seale, Jonathan P.; Testor, Gerard; Heitsch, Fabian; Meixner, Margaret; Sewilo, Marta

2010-01-01

The H II complex N 159 in the Large Magellanic Cloud is used to study massive star formation in different environments, as it contains three giant molecular clouds (GMCs) that have similar sizes and masses but exhibit different intensities of star formation. We identify candidate massive young stellar objects (YSOs) using infrared photometry, and model their spectral energy distributions to constrain mass and evolutionary state. Good fits are obtained for less evolved Type I, I/II, and II sources. Our analysis suggests that there are massive embedded YSOs in N 159B, a maser source, and several ultracompact H II regions. Massive O-type YSOs are found in GMCs N 159-E and N 159-W, which are associated with ionized gas, i.e., where massive stars formed a few Myr ago. The third GMC, N 159-S, has neither O-type YSOs nor evidence of previous massive star formation. This correlation between current and antecedent formation of massive stars suggests that energy feedback is relevant. We present evidence that N 159-W is forming YSOs spontaneously, while collapse in N 159-E may be triggered. Finally, we compare star formation rates determined from YSO counts with those from integrated Hα and 24 μm luminosities and expected from gas surface densities. Detailed dissection of extragalactic GMCs like the one presented here is key to revealing the physics underlying commonly used star formation scaling laws.

THE MASSIVE STAR POPULATION IN M101. I. THE IDENTIFICATION AND SPATIAL DISTRIBUTION OF THE VISUALLY LUMINOUS STARS

International Nuclear Information System (INIS)

Grammer, Skyler; Humphreys, Roberta M.

2013-01-01

An increasing number of non-terminal giant eruptions are being observed by modern supernova and transient surveys. But very little is known about the origin of these giant eruptions and their progenitors, many of which are presumably very massive, evolved stars. Motivated by the small number of progenitors positively associated with these giant eruptions, we have begun a survey of the evolved massive star populations in nearby galaxies. The nearby, nearly face-on, giant spiral M101 is an excellent laboratory for studying a large population of very massive stars. In this paper, we present BVI photometry obtained from archival HST/ACS Wide Field Camera images of M101. We have produced a catalog of luminous stars with photometric errors <10% for V < 24.5 and 50% completeness down to V ∼ 26.5 even in regions of high stellar crowding. Using color and luminosity criteria, we have identified candidate luminous OB-type stars and blue supergiants, yellow supergiants, and red supergiants for future observation. We examine their spatial distributions across the face of M101 and find that the ratio of blue to red supergiants decreases by two orders of magnitude over the radial extent of M101 corresponding to 0.5 dex in metallicity. We discuss the resolved stellar content in the giant star-forming complexes NGC 5458, 5453, 5461, 5451, 5462, and 5449 and discuss their color-magnitude diagrams in conjunction with the spatial distribution of the stars to determine their spatio-temporal formation histories

EARLY-STAGE MASSIVE STAR FORMATION NEAR THE GALACTIC CENTER: Sgr C

Energy Technology Data Exchange (ETDEWEB)

Kendrew, S.; Johnston, K.; Beuther, H. [Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany); Ginsburg, A.; Bally, J.; Battersby, C. [CASA, University of Colorado at Boulder, UCB 389, Boulder, CO 80309 (United States); Cyganowski, C. J., E-mail: kendrew@mpia.de [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)

2013-10-01

We present near-infrared spectroscopy and 1 mm line and continuum observations of a recently identified site of high mass star formation likely to be located in the Central Molecular Zone (CMZ) near Sgr C. Located on the outskirts of the massive evolved H II region associated with Sgr C, the area is characterized by an Extended Green Object (EGO) measuring ∼10'' in size (0.4 pc), whose observational characteristics suggest the presence of an embedded massive protostar driving an outflow. Our data confirm that early-stage star formation is taking place on the periphery of the Sgr C H II region, with detections of two protostellar cores and several knots of H{sub 2} and Brackett γ emission alongside a previously detected compact radio source. We calculate the cores' joint mass to be ∼10{sup 3} M {sub ☉}, with column densities of 1-2 × 10{sup 24} cm{sup –2}. We show the host molecular cloud to hold ∼10{sup 5} M {sub ☉} of gas and dust with temperatures and column densities favorable for massive star formation to occur, however, there is no evidence of star formation outside of the EGO, indicating that the cloud is predominantly quiescent. Given its mass, density, and temperature, the cloud is comparable to other remarkable non-star-forming clouds such as G0.253 in the eastern CMZ.

High molecular gas fractions in normal massive star-forming galaxies in the young Universe.

Science.gov (United States)

Tacconi, L J; Genzel, R; Neri, R; Cox, P; Cooper, M C; Shapiro, K; Bolatto, A; Bouché, N; Bournaud, F; Burkert, A; Combes, F; Comerford, J; Davis, M; Schreiber, N M Förster; Garcia-Burillo, S; Gracia-Carpio, J; Lutz, D; Naab, T; Omont, A; Shapley, A; Sternberg, A; Weiner, B

2010-02-11

Stars form from cold molecular interstellar gas. As this is relatively rare in the local Universe, galaxies like the Milky Way form only a few new stars per year. Typical massive galaxies in the distant Universe formed stars an order of magnitude more rapidly. Unless star formation was significantly more efficient, this difference suggests that young galaxies were much more molecular-gas rich. Molecular gas observations in the distant Universe have so far largely been restricted to very luminous, rare objects, including mergers and quasars, and accordingly we do not yet have a clear idea about the gas content of more normal (albeit massive) galaxies. Here we report the results of a survey of molecular gas in samples of typical massive-star-forming galaxies at mean redshifts of about 1.2 and 2.3, when the Universe was respectively 40% and 24% of its current age. Our measurements reveal that distant star forming galaxies were indeed gas rich, and that the star formation efficiency is not strongly dependent on cosmic epoch. The average fraction of cold gas relative to total galaxy baryonic mass at z = 2.3 and z = 1.2 is respectively about 44% and 34%, three to ten times higher than in today's massive spiral galaxies. The slow decrease between z approximately 2 and z approximately 1 probably requires a mechanism of semi-continuous replenishment of fresh gas to the young galaxies.

SUBSTELLAR-MASS COMPANIONS TO THE K-DWARF BD+14 4559 AND THE K-GIANTS HD 240210 AND BD+20 2457

International Nuclear Information System (INIS)

Niedzielski, A.; Nowak, G.; Adamow, M.; Wolszczan, A.

2009-01-01

We present the discovery of substellar-mass companions to three stars by the ongoing Penn State-Torun Planet Search conducted with the 9.2 m Hobby-Eberly Telescope. The K2-dwarf, BD+14 4559, has a 1.5 M J minimum mass companion with the orbital period of 269 days and shows a non-linear, long-term radial velocity (RV) trend, which indicates a possible presence of another planet-mass body in the system. The K3-giant, HD 240210, exhibits RV variations that require modeling with multiple orbits, but the available data are not yet sufficient to do it unambiguously. A tentative, one-planet model calls for a 5.2 M J minimum mass planet in a 502 day orbit around the star. The most massive of the three stars, the K2-giant, BD+20 2457, whose estimated mass is 2.8 ± 1.5 M sun , has two companions with the respective minimum masses of 21.4 M J and 12.5 M J and orbital periods of 380 and 622 days. Depending on the unknown inclinations of the orbits, the currently very uncertain mass of the star, and the dynamical properties of the system, it may represent the first detection of two brown dwarf-mass companions orbiting a giant. The existence of such objects will have consequences for the interpretation of the so-called brown dwarf desert known to exist in the case of solar-mass stars.

Spontaneous scalarization with an extremely massive field and heavy neutron stars

Science.gov (United States)

Morisaki, Soichiro; Suyama, Teruaki

2017-10-01

We investigate the internal structure and the mass-radius relation of neutron stars in a recently proposed scalar-tensor theory dubbed asymmetron in which a massive scalar field undergoes spontaneous scalarization inside neutron stars. We focus on the case where the Compton wavelength is shorter than 10 km, which has not been investigated in the literature. By solving the modified Einstein equations, either purely numerically or by partially using a semianalytic method, we find that not only the weakening of gravity by spontaneous scalarization but also the scalar force affect the internal structure significantly in the massive case. We also find that the maximum mass of neutron stars is larger for certain parameter sets than that in general relativity and reaches 2 M⊙ even if the effect of strange hadrons is taken into account. There is even a range of parameters where the maximum mass of neutron stars largely exceeds the threshold that violates the causality bound in general relativity.

Simulating the Birth of Massive Star Clusters: Is Destruction Inevitable?

Science.gov (United States)

Rosen, Anna

2013-10-01

Very early in its operation, the Hubble Space Telescope {HST} opened an entirely new frontier: study of the demographics and properties of star clusters far beyond the Milky Way. However, interpretation of HST's observations has proven difficult, and has led to the development of two conflicting models. One view is that most massive star clusters are disrupted during their infancy by feedback from newly formed stars {i.e., "infant mortality"}, independent of cluster mass or environment. The other model is that most star clusters survive their infancy and are disrupted later by mass-dependent dynamical processes. Since observations at present have failed to discriminate between these views, we propose a theoretical investigation to provide new insight. We will perform radiation-hydrodynamic simulations of the formation of massive star clusters, including for the first time a realistic treatment of the most important stellar feedback processes. These simulations will elucidate the physics of stellar feedback, and allow us to determine whether cluster disruption is mass-dependent or -independent. We will also use our simulations to search for observational diagnostics that can distinguish bound from unbound clusters, and to predict how cluster disruption affects the cluster luminosity function in a variety of galactic environments.

THE MASSIVE STAR-FORMING REGION CYGNUS OB2. II. INTEGRATED STELLAR PROPERTIES AND THE STAR FORMATION HISTORY

International Nuclear Information System (INIS)

Wright, N. J.; Drake, J. J.; Drew, J. E.; Vink, J. S.

2010-01-01

Cygnus OB2 is the nearest example of a massive star-forming region (SFR), containing over 50 O-type stars and hundreds of B-type stars. We have analyzed the properties of young stars in two fields in Cyg OB2 using the recently published deep catalog of Chandra X-ray point sources with complementary optical and near-IR photometry. Our sample is complete to ∼1 M sun (excluding A- and B-type stars that do not emit X-rays), making this the deepest study of the stellar properties and star formation history in Cyg OB2 to date. From Siess et al. isochrone fits to the near-IR color-magnitude diagram, we derive ages of 3.5 +0.75 -1.0 and 5.25 +1.5 -1.0 Myr for sources in the two fields, both with considerable spreads around the pre-main-sequence isochrones. The presence of a stellar population somewhat older than the present-day O-type stars, also fits in with the low fraction of sources with inner circumstellar disks (as traced by the K-band excess) that we find to be very low, but appropriate for a population of age ∼5 Myr. We also find that the region lacks a population of highly embedded sources that is often observed in young SFRs, suggesting star formation in the vicinity has declined. We measure the stellar mass functions (MFs) in this limit and find a power-law slope of Γ = -1.09 ± 0.13, in good agreement with the global mean value estimated by Kroupa. A steepening of the slope at higher masses is observed and suggested as due to the presence of the previous generation of stars that have lost their most massive members. Finally, combining our MF and an estimate of the radial density profile of the association suggests a total mass of Cyg OB2 of ∼3 x 10 4 M sun , similar to that of many of our Galaxy's most massive SFRs.

Evidence for Nemesis: a solar companion star

International Nuclear Information System (INIS)

Muller, R.A.

1985-01-01

The evidence that the sun has a companion star ''Nemesis'' responsible for periodic mass extinctions is reviewed. A gaussian ideogram of the rates of family extinctions in the oceans shows periods of 26 and 30 Myr. Analysis of impact cratering on the earth shows a period of either 28.4 or 30 Myr, depending on the crater selection. Models which attempt to explain these periods with either oscillations through the galactic plane, or through the effects of a tenth planet, are seriously flawed. If the periods seen in the data are real (and not a spurious result of a statistical fluctuation) then the ''Nemesis hypothesis'' is the only suggested explanation that has survived close scrutiny. The Nemesis model predicts that the impacts took place during brief storms of several million years duration, perhaps accounting for the ''extended'' nature of the mass extinctions. A search for Nemesis is under way at Berkeley. 18 refs., 4 figs

A SPECTROSCOPIC SURVEY OF MASSIVE STARS IN M31 AND M33

Energy Technology Data Exchange (ETDEWEB)

Massey, Philip; Neugent, Kathryn F.; Smart, Brianna M., E-mail: phil.massey@lowell.edu, E-mail: kneugent@lowell.edu, E-mail: bsmart@astro.wisc.edu [Lowell Observatory, 1400 W Mars Hill Road, Flagstaff, AZ 86001 (United States)

2016-09-01

We describe our spectroscopic follow-up to the Local Group Galaxy Survey (LGGS) photometry of M31 and M33. We have obtained new spectroscopy of 1895 stars, allowing us to classify 1496 of them for the first time. Our study has identified many foreground stars, and established membership for hundreds of early- and mid-type supergiants. We have also found nine new candidate luminous blue variables and a previously unrecognized Wolf–Rayet star. We republish the LGGS M31 and M33 catalogs with improved coordinates, and including spectroscopy from the literature and our new results. The spectroscopy in this paper is responsible for the vast majority of the stellar classifications in these two nearby spiral neighbors. The most luminous (and hence massive) of the stars in our sample are early-type B supergiants, as expected; the more massive O stars are more rare and fainter visually, and thus mostly remain unobserved so far. The majority of the unevolved stars in our sample are in the 20–40 M {sub ⊙} range.

Classical Cepheid luminosities from binary companions

International Nuclear Information System (INIS)

Evans, N.R.

1991-01-01

Luminosities for the classical Cepheids Eta Aql, W Sgr, and SU Cas are determined from IUE spectra of their binary companions. Spectral types of the companions are determined from the spectra by comparison with the spectra of standard stars. The absolute magnitude inferred from these spectral types is used to determine the absolute magnitude of the Cepheid, either directly or from the magnitude difference between the two stars. For the temperature range of the companions (A0 V), distinctions of a quarter of a spectral subclass can be made in the comparison between the companions and standard stars. The absolute magnitudes for Eta Aql and W Sgr agree well with the period-luminosity-color relation of Feast and Walker (1987). Random errors are estimated to be 0.3 mag. SU Cas, however, is overluminous for pulsation in the fundamental mode, implying that it is pulsating in an overtone. 58 refs

Evolution of massive stars in very young clusters and associations

International Nuclear Information System (INIS)

Stothers, R.B.

1985-01-01

The stellar content of very young galactic clusters and associations with well-determined ages has been analyzed statistically to derive information about stellar evolution at high masses. The adopted approach is semiempirical and uses natural spectroscopic groups of stars on the H-R diagram, together with the stars' apparent magnitudes. Cluster distance moduli are not used. Only the most basic elements of stellar evolution theory are required as input. For stellar aggregates with main-sequence turnups at spectral types between O9 and B2, the following conclusions have emerged: (1) O-type main-sequence stars evolve to a spectral type of B1 during core hydrogen burning; (2) most of the O-type blue stragglers are newly formed massive stars, burning core hydrogen; (3) supergiants lying redward of the turnup, as well as most, or all, of the Wolf-Rayet stars, are burning core helium; (4) Wolf-Rayet stars originally had masses greater than 30--40 M/sub sun/, while known M-type supergiants evolved from star less massive than approx.30 M/sub sun/; (5) phases of evolution following core helium burning are unobservably rapid, presumably on account of copious neutrino emission; and (6) formation of stars of high mass continues vigorously in most young clusters and association for approx.8 x 10 6 yr. The important result concerning the evolutionary status of the supergiants depends only on the total number of these stars and not on how they are distributed between blue and red types; the result, however, may be sensitive to the assumed amount of convective core overshooting. Conclusions in the present work refer chiefly to luminous stars in the mass range 10--40 M/sub sun/, belonging to aggregates in the age range (6--25) x 10 6 yr

Massive star formation by accretion. II. Rotation: how to circumvent the angular momentum barrier?

Science.gov (United States)

Haemmerlé, L.; Eggenberger, P.; Meynet, G.; Maeder, A.; Charbonnel, C.; Klessen, R. S.

2017-06-01

Context. Rotation plays a key role in the star-formation process, from pre-stellar cores to pre-main-sequence (PMS) objects. Understanding the formation of massive stars requires taking into account the accretion of angular momentum during their PMS phase. Aims: We study the PMS evolution of objects destined to become massive stars by accretion, focusing on the links between the physical conditions of the environment and the rotational properties of young stars. In particular, we look at the physical conditions that allow the production of massive stars by accretion. Methods: We present PMS models computed with a new version of the Geneva Stellar Evolution code self-consistently including accretion and rotation according to various accretion scenarios for mass and angular momentum. We describe the internal distribution of angular momentum in PMS stars accreting at high rates and we show how the various physical conditions impact their internal structures, evolutionary tracks, and rotation velocities during the PMS and the early main sequence. Results: We find that the smooth angular momentum accretion considered in previous studies leads to an angular momentum barrier and does not allow the formation of massive stars by accretion. A braking mechanism is needed in order to circumvent this angular momentum barrier. This mechanism has to be efficient enough to remove more than two thirds of the angular momentum from the inner accretion disc. Due to the weak efficiency of angular momentum transport by shear instability and meridional circulation during the accretion phase, the internal rotation profiles of accreting stars reflect essentially the angular momentum accretion history. As a consequence, careful choice of the angular momentum accretion history allows circumvention of any limitation in mass and velocity, and production of stars of any mass and velocity compatible with structure equations.

A Substellar Companion to Pleiades HII 3441

Science.gov (United States)

Konishi, Mihoko; Matsuo, Taro; Yamamoto, Kodai; Samland, Matthias; Sudo, Jun; Shibai, Hiroshi; Itoh, Yoichi; Fukagawa, Misato; Sumi, Takhiro; Kudo, Tomoyuki;

Models of the circumstellar medium of evolving, massive runaway stars moving through the Galactic plane

NARCIS (Netherlands)

Meyer, D.M.-A.; Mackey, J.; Langer, N.; Gvaramadze, V.V.; Mignone, A.; Izzard, R.G.; Kaper, L.

2014-01-01

At least 5 per cent of the massive stars are moving supersonically through the interstellar medium (ISM) and are expected to produce a stellar wind bow shock. We explore how the mass-loss and space velocity of massive runaway stars affect the morphology of their bow shocks. We run two-dimensional

The Galactic Distribution of Massive Star Formation from the Red MSX Source Survey

Science.gov (United States)

Figura, Charles C.; Urquhart, J. S.

2013-01-01

Massive stars inject enormous amounts of energy into their environments in the form of UV radiation and molecular outflows, creating HII regions and enriching local chemistry. These effects provide feedback mechanisms that aid in regulating star formation in the region, and may trigger the formation of subsequent generations of stars. Understanding the mechanics of massive star formation presents an important key to understanding this process and its role in shaping the dynamics of galactic structure. The Red MSX Source (RMS) survey is a multi-wavelength investigation of ~1200 massive young stellar objects (MYSO) and ultra-compact HII (UCHII) regions identified from a sample of colour-selected sources from the Midcourse Space Experiment (MSX) point source catalog and Two Micron All Sky Survey. We present a study of over 900 MYSO and UCHII regions investigated by the RMS survey. We review the methods used to determine distances, and investigate the radial galactocentric distribution of these sources in context with the observed structure of the galaxy. The distribution of MYSO and UCHII regions is found to be spatially correlated with the spiral arms and galactic bar. We examine the radial distribution of MYSOs and UCHII regions and find variations in the star formation rate between the inner and outer Galaxy and discuss the implications for star formation throughout the galactic disc.

Bulk yields of nucleosynthesis from massive stars

International Nuclear Information System (INIS)

Arnett, W.D.

1978-01-01

Preliminary estimates are made of the absolute yields of abundant nuclei synthesized in observed stars. The compositions of nine helium stars of mass 3 or =10M/sub sun/ is estimated. A variety of choices for the initial mass function (IMF) are used to calculate the yield per stellar generation. For standard choices of the (IMF) the absolute and relative yields of 12 C, 16 O, 20 Ne, 24 Mg, the Si to Ca group, and the iron group agree with solar system values, to the accuracy of the calculations. The relative yields are surprisingly insensitive to the slope of the IMF. In a second approach, using standard estimates (Ostriker, Richstone, and Thuan) for the current rate of stellar death, I find the present rate of nucleosynthesis in the solar neighborhood to be about 10%of the average rate over galactic history. This result is consistent with many standard models of galactic evolution (for example, the Schmidt model in which star formation goes as gas density squared). It appears that if the star formation rate is high enough to produce the stars we see around us, then the nucleosynthesis rate is large enough to produce the processed nuclei (except 4 He) seen in those stars. The typical nucleosynthesis source is massive (Mapprox. =30 M/sub sun/); the death rate of such stars is a small fraction (3-10%) of recent estimates of the total rate of supernovae

Massive stars and the energy balance of the ISM: I. The imapct of an isolated 60 M star

Science.gov (United States)

Yorke, H. W.; Freyer, T.; Hensler, G.

2002-01-01

We present results of numerical simulations carried out with a 2D radiation hydrodynamics code in order to study the impact of massive stars on their surrounding interstellar medium. This first paper deals with the evolution of the circumstellar gas around an isolated 60 M star.

Low-metallicity massive single stars with rotation. Evolutionary models applicable to I Zwicky 18

NARCIS (Netherlands)

Szécsi, D.; Langer, N.; Yoon, S.C.; Sanyal, D.; de Mink, S.; Evans, C.J.; Dermine, T.

2015-01-01

Context. Low-metallicity environments such as the early Universe and compact star-forming dwarf galaxies contain many massive stars. These stars influence their surroundings through intense UV radiation, strong winds and explosive deaths. A good understanding of low-metallicity environments requires

Formation of new stellar populations from gas accreted by massive young star clusters.

Science.gov (United States)

Li, Chengyuan; de Grijs, Richard; Deng, Licai; Geller, Aaron M; Xin, Yu; Hu, Yi; Faucher-Giguère, Claude-André

2016-01-28

Stars in clusters are thought to form in a single burst from a common progenitor cloud of molecular gas. However, massive, old 'globular' clusters--those with ages greater than ten billion years and masses several hundred thousand times that of the Sun--often harbour multiple stellar populations, indicating that more than one star-forming event occurred during their lifetimes. Colliding stellar winds from late-stage, asymptotic-giant-branch stars are often suggested to be triggers of second-generation star formation. For this to occur, the initial cluster masses need to be greater than a few million solar masses. Here we report observations of three massive relatively young star clusters (1-2 billion years old) in the Magellanic Clouds that show clear evidence of burst-like star formation that occurred a few hundred million years after their initial formation era. We show that such clusters could have accreted sufficient gas to form new stars if they had orbited in their host galaxies' gaseous disks throughout the period between their initial formation and the more recent bursts of star formation. This process may eventually give rise to the ubiquitous multiple stellar populations in globular clusters.

Galaxy growth in a massive halo in the first billion years of cosmic history

Science.gov (United States)

Marrone, D. P.; Spilker, J. S.; Hayward, C. C.; Vieira, J. D.; Aravena, M.; Ashby, M. L. N.; Bayliss, M. B.; Béthermin, M.; Brodwin, M.; Bothwell, M. S.; Carlstrom, J. E.; Chapman, S. C.; Chen, Chian-Chou; Crawford, T. M.; Cunningham, D. J. M.; De Breuck, C.; Fassnacht, C. D.; Gonzalez, A. H.; Greve, T. R.; Hezaveh, Y. D.; Lacaille, K.; Litke, K. C.; Lower, S.; Ma, J.; Malkan, M.; Miller, T. B.; Morningstar, W. R.; Murphy, E. J.; Narayanan, D.; Phadke, K. A.; Rotermund, K. M.; Sreevani, J.; Stalder, B.; Stark, A. A.; Strandet, M. L.; Tang, M.; Weiß, A.

2018-01-01

According to the current understanding of cosmic structure formation, the precursors of the most massive structures in the Universe began to form shortly after the Big Bang, in regions corresponding to the largest fluctuations in the cosmic density field. Observing these structures during their period of active growth and assembly—the first few hundred million years of the Universe—is challenging because it requires surveys that are sensitive enough to detect the distant galaxies that act as signposts for these structures and wide enough to capture the rarest objects. As a result, very few such objects have been detected so far. Here we report observations of a far-infrared-luminous object at redshift 6.900 (less than 800 million years after the Big Bang) that was discovered in a wide-field survey. High-resolution imaging shows it to be a pair of extremely massive star-forming galaxies. The larger is forming stars at a rate of 2,900 solar masses per year, contains 270 billion solar masses of gas and 2.5 billion solar masses of dust, and is more massive than any other known object at a redshift of more than 6. Its rapid star formation is probably triggered by its companion galaxy at a projected separation of 8 kiloparsecs. This merging companion hosts 35 billion solar masses of stars and has a star-formation rate of 540 solar masses per year, but has an order of magnitude less gas and dust than its neighbour and physical conditions akin to those observed in lower-metallicity galaxies in the nearby Universe. These objects suggest the presence of a dark-matter halo with a mass of more than 100 billion solar masses, making it among the rarest dark-matter haloes that should exist in the Universe at this epoch.

A LIKELY CLOSE-IN LOW-MASS STELLAR COMPANION TO THE TRANSITIONAL DISK STAR HD 142527

International Nuclear Information System (INIS)

Biller, Beth; Benisty, Myriam; Chauvin, Gael; Olofsson, Johan; Pott, Jörg-Uwe; Müller, André; Bonnefoy, Mickaël; Henning, Thomas; Lacour, Sylvestre; Thebault, Philippe; Juhász, Attila; Sicilia-Aguilar, Aurora; Tuthill, Peter; Crida, Aurelien

2012-01-01

With the uniquely high contrast within 0.''1 (Δmag(L') = 5-6.5 mag) available using Sparse Aperture Masking with NACO at Very Large Telescope, we detected asymmetry in the flux from the Herbig Fe star HD 142527 with a barycenter emission situated at a projected separation of 88 ± 5 mas (12.8 ± 1.5 AU at 145 pc) and flux ratios in H, K, and L' of 0.016 ± 0.007, 0.012 ± 0.008, and 0.0086 ± 0.0011, respectively (3σ errors), relative to the primary star and disk. After extensive closure-phase modeling, we interpret this detection as a close-in, low-mass stellar companion with an estimated mass of ∼0.1-0.4 M ☉ . HD 142527 has a complex disk structure, with an inner gap imaged in both the near and mid-IR as well as a spiral feature in the outer disk in the near-IR. This newly detected low-mass stellar companion may provide a critical explanation of the observed disk structure.

Kinematics of the inner thousand AU region around the young massive star AFGL 2591-VLA3: a massive disk candidate?

NARCIS (Netherlands)

Wang, K. -S.; van der Tak, F. F. S.; Hogerheijde, M. R.

Context. Recent detections of disks around young high-mass stars support the idea of massive star formation through accretion rather than coalescence, but the detailed kinematics in the equatorial region of the disk candidates is not well known, which limits our understanding of the accretion

THE SIZE-STAR FORMATION RELATION OF MASSIVE GALAXIES AT 1.5 < z < 2.5

International Nuclear Information System (INIS)

Toft, S.; Franx, M.; Van Dokkum, P.; Foerster Schreiber, N. M.; Labbe, I.; Wuyts, S.; Marchesini, D.

2009-01-01

We study the relation between size and star formation activity in a complete sample of 225 massive (M * > 5 x 10 10 M sun ) galaxies at 1.5 PSF ∼ 0.''45) ground-based ISAAC data, we confirm and improve the significance of the relation between star formation activity and compactness found in previous studies, using a large, complete mass-limited sample. At z ∼ 2, massive quiescent galaxies are significantly smaller than massive star-forming galaxies, and a median factor of 0.34 ± 0.02 smaller than galaxies of similar mass in the local universe. Thirteen percent of the quiescent galaxies are unresolved in the ISAAC data, corresponding to sizes <1 kpc, more than five times smaller than galaxies of similar mass locally. The quiescent galaxies span a Kormendy relation which, compared to the relation for local early types, is shifted to smaller sizes and brighter surface brightnesses and is incompatible with passive evolution. The progenitors of the quiescent galaxies were likely dominated by highly concentrated, intense nuclear starbursts at z ∼ 3-4, in contrast to star-forming galaxies at z ∼ 2 which are extended and dominated by distributed star formation.

YOUNG STELLAR OBJECTS IN THE MASSIVE STAR-FORMING REGION W49

Energy Technology Data Exchange (ETDEWEB)

Saral, G.; Hora, J. L.; Willis, S. E. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Koenig, X. P. [Yale University, Department of Astronomy, 208101, New Haven, CT 06520-8101 (United States); Gutermuth, R. A. [University of Massachusetts, Department of Astronomy, Amherst, MA 01003 (United States); Saygac, A. T., E-mail: gsaral@cfa.harvard.edu [Istanbul University, Faculty of Science, Astronomy and Space Sciences Department, Istanbul-Turkey (Turkey)

2015-11-01

We present the initial results of our investigation of the star-forming complex W49, one of the youngest and most luminous massive star-forming regions in our Galaxy. We used Spitzer/Infrared Array Camera (IRAC) data to investigate massive star formation with the primary objective of locating a representative set of protostars and the clusters of young stars that are forming around them. We present our source catalog with the mosaics from the IRAC data. In this study we used a combination of IRAC, MIPS, Two Micron All Sky Survey, and UKIRT Deep Infrared Sky Survey (UKIDSS) data to identify and classify the young stellar objects (YSOs). We identified 232 Class 0/I YSOs, 907 Class II YSOs, and 74 transition disk candidate objects using color–color and color–magnitude diagrams. In addition, to understand the evolution of star formation in W49, we analyzed the distribution of YSOs in the region to identify clusters using a minimal spanning tree method. The fraction of YSOs that belong to clusters with ≥7 members is found to be 52% for a cutoff distance of 96″, and the ratio of Class II/I objects is 2.1. We compared the W49 region to the G305 and G333 star-forming regions and concluded that W49 has the richest population, with seven subclusters of YSOs.

Close companion to α Ursae Majoris

International Nuclear Information System (INIS)

Kondo, Y.; Morgan, T.H.; Modisette, J.L.

1977-01-01

After our recent article on the chromospheric emission features of the Mg II resonance doublet near 2800 A observed in α UMa, Bidelman pointed out to us that this star's close companion is considerably brighter than is stated in the Yale Catalogue of Bright Stars. We have synthesized the Mg II feature for this star from the Mg II observations obtained in other single stars. The results show that the close companion to α UMa is late A in type, in general agreement with the spectroscopic studies. This explains the apparent discrepancy in the Mg II doublet emission strengths between α UMa and β Gem

Stellar and wind parameters of massive stars from spectral analysis

Science.gov (United States)

Araya, Ignacio; Curé, Michel

2017-11-01

The only way to deduce information from stars is to decode the radiation it emits in an appropriate way. Spectroscopy can solve this and derive many properties of stars. In this work we seek to derive simultaneously the stellar and wind characteristics of a wide range of massive stars. Our stellar properties encompass the effective temperature, the surface gravity, the stellar radius, the micro-turbulence velocity, the rotational velocity and the Si abundance. For wind properties we consider the mass-loss rate, the terminal velocity and the line-force parameters α, k and δ (from the line-driven wind theory). To model the data we use the radiative transport code Fastwind considering the newest hydrodynamical solutions derived with Hydwind code, which needs stellar and line-force parameters to obtain a wind solution. A grid of spectral models of massive stars is created and together with the observed spectra their physical properties are determined through spectral line fittings. These fittings provide an estimation about the line-force parameters, whose theoretical calculations are extremely complex. Furthermore, we expect to confirm that the hydrodynamical solutions obtained with a value of δ slightly larger than ~ 0.25, called δ-slow solutions, describe quite reliable the radiation line-driven winds of A and late B supergiant stars and at the same time explain disagreements between observational data and theoretical models for the Wind-Momentum Luminosity Relationship (WLR).

Uncertainties in s-process nucleosynthesis in massive stars determined by Monte Carlo variations

Science.gov (United States)

Nishimura, N.; Hirschi, R.; Rauscher, T.; St. J. Murphy, A.; Cescutti, G.

2017-08-01

The s-process in massive stars produces the weak component of the s-process (nuclei up to A ˜ 90), in amounts that match solar abundances. For heavier isotopes, such as barium, production through neutron capture is significantly enhanced in very metal-poor stars with fast rotation. However, detailed theoretical predictions for the resulting final s-process abundances have important uncertainties caused both by the underlying uncertainties in the nuclear physics (principally neutron-capture reaction and β-decay rates) as well as by the stellar evolution modelling. In this work, we investigated the impact of nuclear-physics uncertainties relevant to the s-process in massive stars. Using a Monte Carlo based approach, we performed extensive nuclear reaction network calculations that include newly evaluated upper and lower limits for the individual temperature-dependent reaction rates. We found that most of the uncertainty in the final abundances is caused by uncertainties in the neutron-capture rates, while β-decay rate uncertainties affect only a few nuclei near s-process branchings. The s-process in rotating metal-poor stars shows quantitatively different uncertainties and key reactions, although the qualitative characteristics are similar. We confirmed that our results do not significantly change at different metallicities for fast rotating massive stars in the very low metallicity regime. We highlight which of the identified key reactions are realistic candidates for improved measurement by future experiments.

THE ELM SURVEY. V. MERGING MASSIVE WHITE DWARF BINARIES

International Nuclear Information System (INIS)

Brown, Warren R.; Kenyon, Scott J.; Kilic, Mukremin; Gianninas, A.; Allende Prieto, Carlos

2013-01-01

We present the discovery of 17 low-mass white dwarfs (WDs) in short-period (P ≤ 1 day) binaries. Our sample includes four objects with remarkable log g ≅ 5 surface gravities and orbital solutions that require them to be double degenerate binaries. All of the lowest surface gravity WDs have metal lines in their spectra implying long gravitational settling times or ongoing accretion. Notably, six of the WDs in our sample have binary merger times 0.9 M ☉ companions. If the companions are massive WDs, these four binaries will evolve into stable mass transfer AM CVn systems and possibly explode as underluminous supernovae. If the companions are neutron stars, then these may be millisecond pulsar binaries. These discoveries increase the number of detached, double degenerate binaries in the ELM Survey to 54; 31 of these binaries will merge within a Hubble time.

THE ELM SURVEY. V. MERGING MASSIVE WHITE DWARF BINARIES

Energy Technology Data Exchange (ETDEWEB)

Brown, Warren R.; Kenyon, Scott J. [Smithsonian Astrophysical Observatory, 60 Garden St, Cambridge, MA 02138 (United States); Kilic, Mukremin; Gianninas, A. [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W. Brooks St., Norman, OK, 73019 (United States); Allende Prieto, Carlos, E-mail: wbrown@cfa.harvard.edu, E-mail: skenyon@cfa.harvard.edu, E-mail: kilic@ou.edu, E-mail: alexg@nhn.ou.edu, E-mail: callende@iac.es [Instituto de Astrofisica de Canarias, E-38205, La Laguna, Tenerife (Spain)

2013-05-20

We present the discovery of 17 low-mass white dwarfs (WDs) in short-period (P {<=} 1 day) binaries. Our sample includes four objects with remarkable log g {approx_equal} 5 surface gravities and orbital solutions that require them to be double degenerate binaries. All of the lowest surface gravity WDs have metal lines in their spectra implying long gravitational settling times or ongoing accretion. Notably, six of the WDs in our sample have binary merger times <10 Gyr. Four have {approx}>0.9 M{sub Sun} companions. If the companions are massive WDs, these four binaries will evolve into stable mass transfer AM CVn systems and possibly explode as underluminous supernovae. If the companions are neutron stars, then these may be millisecond pulsar binaries. These discoveries increase the number of detached, double degenerate binaries in the ELM Survey to 54; 31 of these binaries will merge within a Hubble time.

Global Infrared–Radio Spectral Energy Distributions of Galactic Massive Star-Forming Regions

Science.gov (United States)

Povich, Matthew Samuel; Binder, Breanna Arlene

2018-01-01

We present a multiwavelength study of 30 Galactic massive star-forming regions. We fit multicomponent dust, blackbody, and power-law continuum models to 3.6 µm through 10 mm spectral energy distributions obtained from Spitzer, MSX, IRAS, Herschel, and Planck archival survey data. Averaged across our sample, ~20% of Lyman continuum photons emitted by massive stars are absorbed by dust before contributing to the ionization of H II regions, while ~50% of the stellar bolometric luminosity is absorbed and reprocessed by dust in the H II regions and surrounding photodissociation regions. The most luminous, infrared-bright regions that fully sample the upper stellar initial mass function (ionizing photon rates NC ≥ 1050 s–1 and total infrared luminosity LTIR ≥ 106.8 L⊙) have higher percentages of absorbed Lyman continuum photons (~40%) and dust-reprocessed starlight (~80%). The monochromatic 70-µm luminosity L70 is linearly correlated with LTIR, and on average L70/LTIR = 50%, in good agreement with extragalactic studies. Calibrated against the known massive stellar content in our sampled H II regions, we find that star formation rates based on L70 are in reasonably good agreement with extragalactic calibrations, when corrected for the smaller physical sizes of the Galactic regions. We caution that absorption of Lyman continuum photons prior to contributing to the observed ionizing photon rate may reduce the attenuation-corrected Hα emission, systematically biasing extragalactic calibrations toward lower star formation rates when applied to spatially-resolved studies of obscured star formation.This work was supported by the National Science Foundation under award CAREER-1454333.

Super massive black hole in galactic nuclei with tidal disruption of stars

International Nuclear Information System (INIS)

Zhong, Shiyan; Berczik, Peter; Spurzem, Rainer

2014-01-01

Tidal disruption of stars by super massive central black holes from dense star clusters is modeled by high-accuracy direct N-body simulation. The time evolution of the stellar tidal disruption rate, the effect of tidal disruption on the stellar density profile, and, for the first time, the detailed origin of tidally disrupted stars are carefully examined and compared with classic papers in the field. Up to 128k particles are used in simulation to model the star cluster around a super massive black hole, and we use the particle number and the tidal radius of the black hole as free parameters for a scaling analysis. The transition from full to empty loss-cone is analyzed in our data, and the tidal disruption rate scales with the particle number, N, in the expected way for both cases. For the first time in numerical simulations (under certain conditions) we can support the concept of a critical radius of Frank and Rees, which claims that most stars are tidally accreted on highly eccentric orbits originating from regions far outside the tidal radius. Due to the consumption of stars moving on radial orbits, a velocity anisotropy is found inside the cluster. Finally we estimate the real galactic center based on our simulation results and the scaling analysis.

Super Massive Black Hole in Galactic Nuclei with Tidal Disruption of Stars

Science.gov (United States)

Zhong, Shiyan; Berczik, Peter; Spurzem, Rainer

2014-09-01

Tidal disruption of stars by super massive central black holes from dense star clusters is modeled by high-accuracy direct N-body simulation. The time evolution of the stellar tidal disruption rate, the effect of tidal disruption on the stellar density profile, and, for the first time, the detailed origin of tidally disrupted stars are carefully examined and compared with classic papers in the field. Up to 128k particles are used in simulation to model the star cluster around a super massive black hole, and we use the particle number and the tidal radius of the black hole as free parameters for a scaling analysis. The transition from full to empty loss-cone is analyzed in our data, and the tidal disruption rate scales with the particle number, N, in the expected way for both cases. For the first time in numerical simulations (under certain conditions) we can support the concept of a critical radius of Frank & Rees, which claims that most stars are tidally accreted on highly eccentric orbits originating from regions far outside the tidal radius. Due to the consumption of stars moving on radial orbits, a velocity anisotropy is found inside the cluster. Finally we estimate the real galactic center based on our simulation results and the scaling analysis.

Thermal generation of the magnetic field in the surface layers of massive stars

Science.gov (United States)

Urpin, V.

2017-11-01

A new magnetic field-generation mechanism based on the Nernst effect is considered in hot massive stars. This mechanism can operate in the upper atmospheres of O and B stars where departures from the LTE form a region with the inverse temperature gradient.

Two massive stars possibly ejected from NGC 3603 via a three-body encounter

Science.gov (United States)

Gvaramadze, V. V.; Kniazev, A. Y.; Chené, A.-N.; Schnurr, O.

2013-03-01

We report the discovery of a bow-shock-producing star in the vicinity of the young massive star cluster NGC 3603 using archival data of the Spitzer Space Telescope. Follow-up optical spectroscopy of this star with Gemini-South led to its classification as O6 V. The orientation of the bow shock and the distance to the star (based on its spectral type) suggest that the star was expelled from the cluster, while the young age of the cluster (˜2 Myr) implies that the ejection was caused by a dynamical few-body encounter in the cluster's core. The relative position on the sky of the O6 V star and a recently discovered O2 If*/WN6 star (located on the opposite side of NGC 3603) allows us to propose that both objects were ejected from the cluster via the same dynamical event - a three-body encounter between a single (O6 V) star and a massive binary (now the O2 If*/WN6 star). If our proposal is correct, then one can `weigh' the O2 If*/WN6 star using the conservation of the linear momentum. Given a mass of the O6 V star of ≈30 M⊙, we found that at the moment of ejection the mass of the O2 If*/WN6 star was ≈175 M⊙. Moreover, the observed X-ray luminosity of the O2 If*/WN6 star (typical of a single star) suggests that the components of this originally binary system have merged (e.g., because of encounter hardening).

NEW M, L, AND T DWARF COMPANIONS TO NEARBY STARS FROM THE WIDE-FIELD INFRARED SURVEY EXPLORER

Energy Technology Data Exchange (ETDEWEB)

Luhman, Kevin L.; Loutrel, Nicholas P.; McCurdy, Nicholas S.; Melso, Nicole D.; Star, Kimberly M.; Terrien, Ryan C. [Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802 (United States); Mace, Gregory N.; McLean, Ian S. [UCLA Division of Astronomy and Astrophysics, Los Angeles, CA 90095 (United States); Young, Michael D.; Rhode, Katherine L. [Department of Astronomy, Indiana University, Swain West 319, 727 East Third Street, Bloomington, IN 47405 (United States); Davy Kirkpatrick, J., E-mail: kluhman@astro.psu.edu [Infrared Processing and Analysis Center, MS 100-22, California Institute of Technology, Pasadena, CA 91125 (United States)

2012-12-01

We present 11 candidate late-type companions to nearby stars identified with data from the Wide-field Infrared Survey Explorer (WISE) and the Two Micron All Sky Survey (2MASS). Eight of the candidates are likely to be companions based on their common proper motions with the primaries. The remaining three objects are rejected as companions, one of which is a free-floating T7 dwarf. Spectral types are available for five of the companions, which consist of M2V, M8.5V, L5, T8, and T8. Based on their photometry, the unclassified companions are probably two mid-M dwarfs and one late-M/early-L dwarf. One of the T8 companions, WISE J142320.84+011638.0, has already been reported by Pinfield and coworkers. The other T8 companion, ULAS J095047.28+011734.3, was discovered by Burningham and coworkers through the United Kingdom Infrared Telescope Infrared Deep Sky Survey, but its companionship has not been previously recognized in the literature. The L5 companion, 2MASS J17430860+8526594, is a new member of a class of L dwarfs that exhibit unusually blue near-IR colors. Among the possible mechanisms that have been previously proposed for the peculiar colors of these L dwarfs, low metallicity does not appear to be a viable explanation for 2MASS J17430860+8526594 since our spectrum of the primary suggests that its metallicity is not significantly subsolar.

NEW M, L, AND T DWARF COMPANIONS TO NEARBY STARS FROM THE WIDE-FIELD INFRARED SURVEY EXPLORER

International Nuclear Information System (INIS)

Luhman, Kevin L.; Loutrel, Nicholas P.; McCurdy, Nicholas S.; Melso, Nicole D.; Star, Kimberly M.; Terrien, Ryan C.; Mace, Gregory N.; McLean, Ian S.; Young, Michael D.; Rhode, Katherine L.; Davy Kirkpatrick, J.

2012-01-01

We present 11 candidate late-type companions to nearby stars identified with data from the Wide-field Infrared Survey Explorer (WISE) and the Two Micron All Sky Survey (2MASS). Eight of the candidates are likely to be companions based on their common proper motions with the primaries. The remaining three objects are rejected as companions, one of which is a free-floating T7 dwarf. Spectral types are available for five of the companions, which consist of M2V, M8.5V, L5, T8, and T8. Based on their photometry, the unclassified companions are probably two mid-M dwarfs and one late-M/early-L dwarf. One of the T8 companions, WISE J142320.84+011638.0, has already been reported by Pinfield and coworkers. The other T8 companion, ULAS J095047.28+011734.3, was discovered by Burningham and coworkers through the United Kingdom Infrared Telescope Infrared Deep Sky Survey, but its companionship has not been previously recognized in the literature. The L5 companion, 2MASS J17430860+8526594, is a new member of a class of L dwarfs that exhibit unusually blue near-IR colors. Among the possible mechanisms that have been previously proposed for the peculiar colors of these L dwarfs, low metallicity does not appear to be a viable explanation for 2MASS J17430860+8526594 since our spectrum of the primary suggests that its metallicity is not significantly subsolar.

Induced massive star formation in the trifid nebula?

Science.gov (United States)

Cernicharo; Lefloch; Cox; Cesarsky; Esteban; Yusef-Zadeh; Mendez; Acosta-Pulido; Garcia Lopez RJ; Heras

1998-10-16

The Trifid nebula is a young (10(5) years) galactic HII region where several protostellar sources have been detected with the infrared space observatory. The sources are massive (17 to 60 solar masses) and are associated with molecular gas condensations at the edges or inside the nebula. They appear to be in an early evolutionary stage and may represent the most recent generation of stars in the Trifid. These sources range from dense, apparently still inactive cores to more evolved sources, undergoing violent mass ejection episodes, including a source that powers an optical jet. These observations suggest that the protostellar sources may have evolved by induced star formation in the Trifid nebula.

Evolution of massive close binaries and formation of neutron stars and black holes

International Nuclear Information System (INIS)

Massevitch, A.G.; Tutukov, A.V.; Yungelson, L.R.

1976-01-01

Main results of computations of evolution for massive close binaries (10 M(Sun)+9.4 M(Sun), 16 M(Sun)+15 M(Sun), 32 M(Sun)+30 M(Sun), 64 M(Sun)+60 M(Sun)) up to oxygen exhaustion in the core are described. Mass exchange starting in core hydrogen, shell hydrogen and core helium burning stages was studied. Computations were performed assuming both the Ledoux and Schwarzschild stability criteria for semiconvection. The influence of UFI-neutrino emission on evolution of close binaries was investigated. The results obtained allow to outline the following evolutionary chain: two detached Main-Sequence stars - mass exchange - Wolf-Rayet star or blue supergiant plus main sequence star - explosion of the initially more massive star appearing as a supernova event - collapsed or neutron star plus Main-Sequence star, that may be observed as a 'runaway star' - mass exchange leading to X-rays emission - collapsed or neutron star plus WR-star or blue supergiant - second explosion of supernova that preferentially disrupts the system and gives birth to two single high spatial velocity pulsars. Numerical estimates concerning the number and properties of WR-stars, pulsars and X-ray sources are presented. The results are in favour of the existence of UFI-neutrino and of the Ledoux criterion for describing semiconvection. Properties of several well-known X-ray sources and the binary pulsar are discussed on base of evolutionary chain of close binaries. (Auth.)

THE MASS DISTRIBUTION OF COMPANIONS TO LOW-MASS WHITE DWARFS

International Nuclear Information System (INIS)

Andrews, Jeff J.; Price-Whelan, Adrian M.; Agüeros, Marcel A.

2014-01-01

Measuring the masses of companions to single-line spectroscopic binary stars is (in general) not possible because of the unknown orbital plane inclination. Even when the mass of the visible star can be measured, only a lower limit can be placed on the mass of the unseen companion. However, since these inclination angles should be isotropically distributed, for a large enough, unbiased sample, the companion mass distribution can be deconvolved from the distribution of observables. In this work, we construct a hierarchical probabilistic model to infer properties of unseen companion stars given observations of the orbital period and projected radial velocity of the primary star. We apply this model to three mock samples of low-mass white dwarfs (LMWDs; M ≲ 0.45 M ☉ ) and a sample of post-common-envelope binaries. We use a mixture of two Gaussians to model the WD and neutron star (NS) companion mass distributions. Our model successfully recovers the initial parameters of these test data sets. We then apply our model to 55 WDs in the extremely low-mass (ELM) WD Survey. Our maximum a posteriori model for the WD companion population has a mean mass μ WD = 0.74 M ☉ , with a standard deviation σ WD = 0.24 M ☉ . Our model constrains the NS companion fraction f NS to be <16% at 68% confidence. We make samples from the posterior distribution publicly available so that future observational efforts may compute the NS probability for newly discovered LMWDs

EVIDENCE FOR DELAYED MASSIVE STAR FORMATION IN THE M17 PROTO-OB ASSOCIATION

International Nuclear Information System (INIS)

Povich, Matthew S.; Whitney, Barbara A.

2010-01-01

Through analysis of archival images and photometry from the Spitzer GLIMPSE and MIPSGAL surveys combined with Two Micron All Sky Survey and MSX data, we have identified 488 candidate young stellar objects (YSOs) in the giant molecular cloud M17 SWex, which extends ∼50 pc southwest from the prominent Galactic H II region M17. Our sample includes >200 YSOs with masses >3 M sun that will become B-type stars on the main sequence. Extrapolating over the stellar initial mass function (IMF), we find that M17 SWex contains >1.3 x 10 4 young stars, representing a proto-OB association. The YSO mass function is significantly steeper than the Salpeter IMF, and early O stars are conspicuously absent from M17 SWex. Assuming M17 SWex will form an OB association with a Salpeter IMF, these results reveal the combined effects of (1) more rapid circumstellar disk evolution in more massive YSOs and (2) delayed onset of massive star formation.

A rare encounter with very massive stars in NGC 3125-A1

Energy Technology Data Exchange (ETDEWEB)

Wofford, Aida [UPMC-CNRS, UMR7095, Institut d' Astrophysique de Paris, F-75014 Paris (France); Leitherer, Claus [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Chandar, Rupali [University of Toledo, Department of Physics and Astronomy, Toledo, OH 43606 (United States); Bouret, Jean-Claude, E-mail: wofford@iap.edu [Aix Marseille Universite, CNRS, LAM (Laboratoire d' Astrophysique de Marseille) UMR 7326, F-13388 Marseille (France)

2014-02-01

Super star cluster A1 in the nearby starburst galaxy NGC 3125 is characterized by broad He II λ1640 emission (FWHM ∼ 1200 km s{sup –1}) of unprecedented strength (equivalent width, EW = 7.1 ± 0.4 Å). Previous attempts to characterize the massive star content in NGC 3125-A1 were hampered by the low resolution of the UV spectrum and the lack of co-spatial panchromatic data. We obtained far-UV to near-IR spectroscopy of the two principal emitting regions in the galaxy with the Space Telescope Imaging Spectrograph and the Cosmic Origins Spectrograph on board the Hubble Space Telescope. We use these data to study three clusters in the galaxy, A1, B1, and B2. We derive cluster ages of 3-4 Myr, intrinsic reddenings of E(B – V) = 0.13, 0.15, and 0.13, and cluster masses of 1.7 × 10{sup 5}, 1.4 × 10{sup 5}, and 1.1 × 10{sup 5} M {sub ☉}, respectively. A1 and B2 show O V λ1371 absorption from massive stars, which is rarely seen in star-forming galaxies, and have Wolf-Rayet (WR) to O star ratios of N(WN5-6)/N(O) = 0.23 and 0.10, respectively. The high N(WN5-6)/N(O) ratio of A1 cannot be reproduced by models that use a normal initial mass function (IMF) and generic WR star line luminosities. We rule out that the extraordinary He II λ1640 emission and O V λ1371 absorption of A1 are due to an extremely flat upper IMF exponent, and suggest that they originate in the winds of very massive (>120 M {sub ☉}) stars. In order to reproduce the properties of peculiar clusters such as A1, the present grid of stellar evolution tracks implemented in Starburst99 needs to be extended to masses >120 M {sub ☉}.

Evolution of a massive binary in a star field

International Nuclear Information System (INIS)

Baranov, A.S.

1984-01-01

The orbital evolution of a massive binary system interacting with a background field of single stars whose phase density is homogeneous in configuration space is considered. The velocity distribution is assumed isotropic up to some limiting value, and a typical field star is regarded as having a velocity much higher than the orbital speed of the pair components. An expression is derived for the transfer of energy from the binary to the field stars. The time evolution of the orbit parameters a, e is established, and the evolution rate is estimated for Kardashev's (1983) model galactic nucleus containing a central black-hole binary. On the above assumptions the components should become twice as close together within only a few tens of millennia, although the picture may change fundamentally if the nucleus is rotating. 13 references

A spectral differential characterization of low-mass companions

Directory of Open Access Journals (Sweden)

Lyubchik Y.

2013-04-01

Full Text Available We present a new approach with which the dynamical mass of low-mass companions around cool stars can be found. In order to discover companions to late-type stars the stellar spectrum is removed. For this we substract two spectra obtained at different orbital phases from each other in order to discover the companion spectrum in the difference spectrum in which the companion lines appear twice (positive and negative signal. The resulting radial velocity difference of these two signals provides the true mass of the companion. For our test case GJ1046, an M2V dwarf with a low-mass companion that most likely is a brown dwarf we select the CO line region in the K-band. We show that the dynamical mass of a faint companion to an M dwarf can be determined using our spectral differential technique. Only if the companion rotates rapidly and has a small radial velocity amplitude due to a high mass, does blending occur for all lines so that our approach fails. In addition to determining the companion mass, we restore the single companion spectrum from the difference spectrum using singular value decomposition.

The Wolf-Rayet Content of the Andromeda Galaxy: What Do Massive Stars Really Do When the Metallicity is Above Solar?

Science.gov (United States)

Massey, Philip

2000-08-01

We are proposing to survey M 31 for Wolf-Rayet stars (WRs) and red supergiants (RSGs), providing much needed information about how massive stars evolve at greater-than-solar metallicities. Our understanding of massive star evolution is hampered by the effects of mass-loss on these stars; at higher metallicities mass-loss effects become ever more pronounced. Our previous work on other Local Group galaxies (Massey & Johnson 1998) has shown that the number of RSGs to WRs correlates well with metallicity, changing by a factor of 6 from NGC 6822 (log O/H+12=8.3) to the inner parts of M 33 (8.7). Our study of five small regions in M 31 suggests that above this value the ratio of RSGs to WRs doesn't change: does this mean that no massive star that becomes a WR spends any time as a RSG at above solar metallicities? We fear instead that our sample (selected, afterall, for containing WR stars) was not sufficiently well-mixed in age to provide useful global values; the study we propose here will survey all of M 31. Detection of WRs will provide fundamental data not only on massive star evolution, but also act as tracers of the most massive stars, and improve our knowledge of recent star-formation in the Andromeda Galaxy.

THE FRAGMENTATION OF MAGNETIZED, MASSIVE STAR-FORMING CORES WITH RADIATIVE FEEDBACK

Energy Technology Data Exchange (ETDEWEB)

Myers, Andrew T.; McKee, Christopher F. [Department of Physics, University of California, Berkeley, Berkeley, CA 94720 (United States); Cunningham, Andrew J. [Lawrence Livermore National Laboratory, P.O. Box 808, L-23, Livermore, CA 94550 (United States); Klein, Richard I. [Department of Astronomy, University of California, Berkeley, Berkeley, CA 94720 (United States); Krumholz, Mark R., E-mail: atmyers@berkeley.edu [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)

2013-04-01

We present a set of three-dimensional, radiation-magnetohydrodynamic calculations of the gravitational collapse of massive (300 M{sub Sun }), star-forming molecular cloud cores. We show that the combined effects of magnetic fields and radiative feedback strongly suppress core fragmentation, leading to the production of single-star systems rather than small clusters. We find that the two processes are efficient at suppressing fragmentation in different regimes, with the feedback most effective in the dense, central region and the magnetic field most effective in more diffuse, outer regions. Thus, the combination of the two is much more effective at suppressing fragmentation than either one considered in isolation. Our work suggests that typical massive cores, which have mass-to-flux ratios of about 2 relative to critical, likely form a single-star system, but that cores with weaker fields may form a small star cluster. This result helps us understand why the observed relationship between the core mass function and the stellar initial mass function holds even for {approx}100 M{sub Sun} cores with many thermal Jeans masses of material. We also demonstrate that a {approx}40 AU Keplerian disk is able to form in our simulations, despite the braking effect caused by the strong magnetic field.

SPECTRAL TYPING OF LATE-TYPE STELLAR COMPANIONS TO YOUNG STARS FROM LOW-DISPERSION NEAR-INFRARED INTEGRAL FIELD UNIT DATA

Energy Technology Data Exchange (ETDEWEB)

Roberts, Lewis C.; Beichman, Charles A.; Burruss, Rick; Ligon, E. Robert; Lockhart, Thomas G.; Roberts, Jennifer E.; Shao, Michael [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Rice, Emily L.; Brenner, Douglas; Oppenheimer, Ben R. [American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024 (United States); Crepp, Justin R.; Dekany, Richard G.; Hillenbrand, Lynne A.; Hinkley, Sasha [California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 (United States); King, David; Parry, Ian R. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 OHA (United Kingdom); Metchev, Stanimir [Department of Physics and Astronomy, State University of New York, Stony Brook, NY 11794-3800 (United States); Pueyo, Laurent; Sivaramakrishnan, Anand; Soummer, Remi, E-mail: lewis.c.roberts@jpl.nasa.gov [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); and others

2012-07-15

We used the Project 1640 near-infrared coronagraph and integral field spectrograph to observe 19 young solar-type stars. Five of these stars are known binary stars and we detected the late-type secondaries and were able to measure their JH spectra with a resolution of R {approx} 30. The reduced, extracted, and calibrated spectra were compared to template spectra from the IRTF spectral library. With this comparison, we test the accuracy and consistency of spectral-type determination with the low-resolution near-infrared spectra from P1640. Additionally, we determine effective temperature and surface gravity of the companions by fitting synthetic spectra calculated with the PHOENIX model atmosphere code. We also present several new epochs of astrometry of each of the systems. Together, these data increase our knowledge and understanding of the stellar make up of these systems. In addition to the astronomical results, the analysis presented helps validate the Project 1640 data reduction and spectral extraction processes and the utility of low-resolution, near-infrared spectra for characterizing late-type companions in multiple systems.

SEARCHING FOR SCATTERERS: HIGH-CONTRAST IMAGING OF YOUNG STARS HOSTING WIDE-SEPARATION PLANETARY-MASS COMPANIONS

Energy Technology Data Exchange (ETDEWEB)

Bryan, Marta L.; Mawet, Dimitri [Cahill Center for Astronomy and Astrophysics, California Institute of Technology, 1200 East California Boulevard, MC 249-17, Pasadena, CA 91125 (United States); Bowler, Brendan P.; Kraus, Adam L. [McDonald Observatory and Department of Astronomy, University of Texas at Austin, Austin, TX 78712 (United States); Knutson, Heather A. [Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 (United States); Hinkley, Sasha [University of Exeter, Physics Department, Stocker Road, Exeter EX4 4QL (United Kingdom); Nielsen, Eric L.; Blunt, Sarah C. [SETI Institute, Carl Sagan Center, 189 Bernardo Avenue, Mountain View, CA 94043 (United States)

2016-08-20

We have conducted an angular differential imaging survey with NIRC2 at Keck in search of close-in substellar companions to a sample of seven systems with confirmed planetary-mass companions (PMCs) on wide orbits (>50 au). These wide-separation PMCs pose significant challenges to all three possible formation mechanisms: core accretion plus scattering, disk instability, and turbulent fragmentation. We explore the possibility that these companions formed closer in and were scattered out to their present-day locations by searching for other massive bodies at smaller separations. The typical sensitivity for this survey is Δ K ∼ 12.5 at 1″. We identify eight candidate companions, whose masses would reach as low as one Jupiter mass if gravitationally bound. From our multi-epoch astrometry we determine that seven of these are conclusively background objects, while the eighth near DH Tau is ambiguous and requires additional monitoring. We rule out the presence of >7 M {sub Jup} bodies in these systems down to 15–50 au that could be responsible for scattering. This result combined with the totality of evidence suggests that dynamical scattering is unlikely to have produced this population of PMCs. We detect orbital motion from the companions ROXs 42B b and ROXs 12 b, and from this determine 95% upper limits on the companions’ eccentricities of 0.58 and 0.83 respectively. Finally, we find that the 95% upper limit on the occurrence rate of additional planets with masses between 5 and 15 M {sub Jup} outside of 40 au in systems with PMCs is 54%.

SEARCHING FOR SCATTERERS: HIGH-CONTRAST IMAGING OF YOUNG STARS HOSTING WIDE-SEPARATION PLANETARY-MASS COMPANIONS

International Nuclear Information System (INIS)

Bryan, Marta L.; Mawet, Dimitri; Bowler, Brendan P.; Kraus, Adam L.; Knutson, Heather A.; Hinkley, Sasha; Nielsen, Eric L.; Blunt, Sarah C.

2016-01-01

We have conducted an angular differential imaging survey with NIRC2 at Keck in search of close-in substellar companions to a sample of seven systems with confirmed planetary-mass companions (PMCs) on wide orbits (>50 au). These wide-separation PMCs pose significant challenges to all three possible formation mechanisms: core accretion plus scattering, disk instability, and turbulent fragmentation. We explore the possibility that these companions formed closer in and were scattered out to their present-day locations by searching for other massive bodies at smaller separations. The typical sensitivity for this survey is Δ K ∼ 12.5 at 1″. We identify eight candidate companions, whose masses would reach as low as one Jupiter mass if gravitationally bound. From our multi-epoch astrometry we determine that seven of these are conclusively background objects, while the eighth near DH Tau is ambiguous and requires additional monitoring. We rule out the presence of >7 M Jup bodies in these systems down to 15–50 au that could be responsible for scattering. This result combined with the totality of evidence suggests that dynamical scattering is unlikely to have produced this population of PMCs. We detect orbital motion from the companions ROXs 42B b and ROXs 12 b, and from this determine 95% upper limits on the companions’ eccentricities of 0.58 and 0.83 respectively. Finally, we find that the 95% upper limit on the occurrence rate of additional planets with masses between 5 and 15 M Jup outside of 40 au in systems with PMCs is 54%.

Rapidly star-forming galaxies adjacent to quasars at redshifts exceeding 6.

Science.gov (United States)

Decarli, R; Walter, F; Venemans, B P; Bañados, E; Bertoldi, F; Carilli, C; Fan, X; Farina, E P; Mazzucchelli, C; Riechers, D; Rix, H-W; Strauss, M A; Wang, R; Yang, Y

2017-05-24

The existence of massive (10 11 solar masses) elliptical galaxies by redshift z ≈ 4 (refs 1, 2, 3; when the Universe was 1.5 billion years old) necessitates the presence of galaxies with star-formation rates exceeding 100 solar masses per year at z > 6 (corresponding to an age of the Universe of less than 1 billion years). Surveys have discovered hundreds of galaxies at these early cosmic epochs, but their star-formation rates are more than an order of magnitude lower. The only known galaxies with very high star-formation rates at z > 6 are, with one exception, the host galaxies of quasars, but these galaxies also host accreting supermassive (more than 10 9 solar masses) black holes, which probably affect the properties of the galaxies. Here we report observations of an emission line of singly ionized carbon ([C ii] at a wavelength of 158 micrometres) in four galaxies at z > 6 that are companions of quasars, with velocity offsets of less than 600 kilometres per second and linear offsets of less than 100 kiloparsecs. The discovery of these four galaxies was serendipitous; they are close to their companion quasars and appear bright in the far-infrared. On the basis of the [C ii] measurements, we estimate star-formation rates in the companions of more than 100 solar masses per year. These sources are similar to the host galaxies of the quasars in [C ii] brightness, linewidth and implied dynamical mass, but do not show evidence for accreting supermassive black holes. Similar systems have previously been found at lower redshift. We find such close companions in four out of the twenty-five z > 6 quasars surveyed, a fraction that needs to be accounted for in simulations. If they are representative of the bright end of the [C ii] luminosity function, then they can account for the population of massive elliptical galaxies at z ≈ 4 in terms of the density of cosmic space.

A RADIO SEARCH FOR PULSAR COMPANIONS TO SLOAN DIGITAL SKY SURVEY LOW-MASS WHITE DWARFS

International Nuclear Information System (INIS)

Agueeros, Marcel A.; Camilo, Fernando; Silvestri, Nicole M.; Anderson, Scott F.; Kleinman, S. J.; Liebert, James W.

2009-01-01

We have conducted a search for pulsar companions to 15 low-mass white dwarfs (LMWDs; M sun ) at 820 MHz with the NRAO Green Bank Telescope (GBT). These LMWDs were spectroscopically identified in the Sloan Digital Sky Survey (SDSS), and do not show the photometric excess or spectroscopic signature associated with a companion in their discovery data. However, LMWDs are believed to evolve in binary systems and to have either a more massive white dwarf (WD) or a neutron star (NS) as a companion. Indeed, evolutionary models of low-mass X-ray binaries, the precursors of millisecond pulsars (MSPs), produce significant numbers of LMWDs, suggesting that the SDSS LMWDs may have NS companions. No convincing pulsar signal is detected in our data. This is consistent with the findings of van Leeuwen et al., who conducted a GBT search for radio pulsations at 340 MHz from unseen companions to eight SDSS WDs (five are still considered LMWDs; the three others are now classified as 'ordinary' WDs). We discuss the constraints our nondetections place on the probability P MSP that the companion to a given LMWD is a radio pulsar in the context of the luminosity and acceleration limits of our search; we find that P MSP +4 -2 %.

Evolution towards and beyond accretion-induced collapse of massive white dwarfs and formation of millisecond pulsars

OpenAIRE

Tauris, Thomas M.; Sanyal, Debashis; Yoon, Sung-Chul; Langer, Norbert

2013-01-01

Millisecond pulsars (MSPs) are generally believed to be old neutron stars (NSs), formed via type Ib/c core-collapse supernovae (SNe), which have been spun up to high rotation rates via accretion from a companion star in a low-mass X-ray binary (LMXB). In an alternative formation channel, NSs are produced via the accretion-induced collapse (AIC) of a massive white dwarf (WD) in a close binary. Here we investigate binary evolution leading to AIC and examine if NSs formed in this way can subsequ...

Stellar Wind Retention and Expulsion in Massive Star Clusters

Science.gov (United States)

Naiman, J. P.; Ramirez-Ruiz, E.; Lin, D. N. C.

2018-05-01

Mass and energy injection throughout the lifetime of a star cluster contributes to the gas reservoir available for subsequent episodes of star formation and the feedback energy budget responsible for ejecting material from the cluster. In addition, mass processed in stellar interiors and ejected as winds has the potential to augment the abundance ratios of currently forming stars, or stars which form at a later time from a retained gas reservoir. Here we present hydrodynamical simulations that explore a wide range of cluster masses, compactnesses, metallicities and stellar population age combinations in order to determine the range of parameter space conducive to stellar wind retention or wind powered gas expulsion in star clusters. We discuss the effects of the stellar wind prescription on retention and expulsion effectiveness, using MESA stellar evolutionary models as a test bed for exploring how the amounts of wind retention/expulsion depend upon the amount of mixing between the winds from stars of different masses and ages. We conclude by summarizing some implications for gas retention and expulsion in a variety of compact (σv ≳ 20 kms-1) star clusters including young massive star clusters (105 ≲ M/M⊙ ≲ 107, age ≲ 500 Myrs), intermediate age clusters (105 ≲ M/M⊙ ≲ 107, age ≈ 1 - 4 Gyrs), and globular clusters (105 ≲ M/M⊙ ≲ 107, age ≳ 10 Gyrs).

COMPANIONS TO NEARBY STARS WITH ASTROMETRIC ACCELERATION. II

International Nuclear Information System (INIS)

Tokovinin, Andrei; Hartung, Markus; Hayward, Thomas L.

2013-01-01

Hipparcos astrometric binaries were observed with the NICI adaptive optics system at Gemini-S, completing the work of Paper I. Among the 65 F, G, and K dwarfs within 67 pc of the Sun studied here, we resolve 18 new subarcsecond companions, remeasure 7 known astrometric pairs, and establish the physical nature of yet another 3 wider companions. The 107 astrometric binaries targeted at Gemini so far have 38 resolved companions with separations under 3''. Modeling shows that bright enough companions with separations on the order of an arcsecond can perturb the Hipparcos astrometry when they are not accounted for in the data reduction. However, the resulting bias of parallax and proper motion is generally below formal errors and such companions cannot produce fake acceleration. This work contributes to the multiplicity statistics of nearby dwarfs by bridging the gap between spectroscopic and visual binaries and by providing estimates of periods and mass ratios for many astrometric binaries.

THE MASS DISTRIBUTION OF COMPANIONS TO LOW-MASS WHITE DWARFS

Energy Technology Data Exchange (ETDEWEB)

Andrews, Jeff J.; Price-Whelan, Adrian M.; Agüeros, Marcel A. [Department of Astronomy, Columbia University, 550 W 120th Street, New York, NY 10027 (United States)

2014-12-20

Measuring the masses of companions to single-line spectroscopic binary stars is (in general) not possible because of the unknown orbital plane inclination. Even when the mass of the visible star can be measured, only a lower limit can be placed on the mass of the unseen companion. However, since these inclination angles should be isotropically distributed, for a large enough, unbiased sample, the companion mass distribution can be deconvolved from the distribution of observables. In this work, we construct a hierarchical probabilistic model to infer properties of unseen companion stars given observations of the orbital period and projected radial velocity of the primary star. We apply this model to three mock samples of low-mass white dwarfs (LMWDs; M ≲ 0.45 M {sub ☉}) and a sample of post-common-envelope binaries. We use a mixture of two Gaussians to model the WD and neutron star (NS) companion mass distributions. Our model successfully recovers the initial parameters of these test data sets. We then apply our model to 55 WDs in the extremely low-mass (ELM) WD Survey. Our maximum a posteriori model for the WD companion population has a mean mass μ{sub WD} = 0.74 M {sub ☉}, with a standard deviation σ{sub WD} = 0.24 M {sub ☉}. Our model constrains the NS companion fraction f {sub NS} to be <16% at 68% confidence. We make samples from the posterior distribution publicly available so that future observational efforts may compute the NS probability for newly discovered LMWDs.

Teetering Stars: Resonant Excitation of Stellar Obliquities by Hot and Warm Jupiters with External Companions

Science.gov (United States)

Anderson, Kassandra; Lai, Dong

2018-04-01

Stellar spin-orbit misalignments (obliquities) in hot Jupiter systems have been extensively probed in recent years thanks to Rossiter-McLaughlin observations. Such obliquities may reveal clues about hot Jupiter dynamical and migration histories. Common explanations for generating stellar obliquities include high-eccentricity migration, or primordial disk misalignment. This talk investigates another mechanism for producing stellar spin-orbit misalignments in systems hosting a close-in giant planet with an external, inclined planetary companion. Spin-orbit misalignment may be excited due to a secular resonance, occurring when the precession rate of the stellar spin axis (due to the inner orbit) becomes comparable to the precession rate of the inner orbital axis (due to the outer companion). Due to the spin-down of the host star via magnetic braking, this resonance may be achieved at some point during the star's main sequence lifetime for a wide range of giant planet masses and orbital architectures. We focus on both hot Jupiters (with orbital periods less than ten days) and warm Jupiters (with orbital periods around tens of days), and identify the outer perburber properties needed to generate substantial obliquities via resonant excitation, in terms of mass, separation, and inclination. For hot Jupiters, the stellar spin axis is strongly coupled to the orbital axis, and resonant excitation of obliquity requires a close perturber, located within 1-2 AU. For warm Jupiters, the spin and orbital axes are more weakly coupled, and the resonance may be achieved for more distant perturbers (at several to tens of AU). Resonant excitation of the stellar obliquity is accompanied by a decrease in the planets' mutual orbital inclination, and can thus erase high mutual inclinations in two-planet systems. Since many warm Jupiters are known to have outer planetary companions at several AU or beyond, stellar obliquities in warm Jupiter systems may be common, regardless of the

Growth of a Massive Young Stellar Object Fed by a Gas Flow from a Companion Gas Clump

Energy Technology Data Exchange (ETDEWEB)

Chen, Xi; Shen, Zhiqiang [Shanghai Astronomical Observatories, Chinese Academy of Science, Nandan Rd. 80, Shanghai (China); Ren, Zhiyuan [National Astronomical Observatories, Chinese Academy of Science, Chaoyang District Datun Rd. A20, Beijing (China); Zhang, Qizhou [Harvard-Smithsonian Center for Astrophysics, 60 Garden St, Cambridge, MA 02138 (United States); Qiu, Keping [School of Astronomy and Space Science, Nanjing University, 22 Hankou Rd., Nanjing, Jiangsu 210093 (China)

2017-02-01

We present a Submillimeter Array (SMA) observation toward the young massive double-core system G350.69-0.49. This system consists of a northeast (NE) diffuse gas bubble and a southwest (SW) massive young stellar object (MYSO), both clearly seen in the Spitzer images. The SMA observations reveal a gas flow between the NE bubble and the SW MYSO in a broad velocity range from 5 to 30 km s{sup −1} with respect to the system velocity. The gas flow is well confined within the interval between the two objects and traces a significant mass transfer from the NE gas bubble to the SW massive core. The transfer flow can supply the material accreted onto the SW MYSO at a rate of 4.2×10{sup −4} M{sub ⊙} yr{sup −1}. The whole system therefore suggests a mode for the mass growth in the MYSO from a gas transfer flow launched from its companion gas clump, despite the driving mechanism of the transfer flow not being fully determined from the current data.

The Orbit of X Persei and Its Neutron Star Companion

Science.gov (United States)

Delgado-Martí, Hugo; Levine, Alan M.; Pfahl, Eric; Rappaport, Saul A.

2001-01-01

We have observed the Be/X-ray pulsar binary system X Per/4U 0352+30 on 61 occasions spanning an interval of 600 days with the PCA instrument on board the Rossi X-Ray Timing Explorer (RXTE). Pulse timing analyses of the 837 s pulsations yield strong evidence for the presence of orbital Doppler delays. We confirm the Doppler delays by using measurements made with the All Sky Monitor (ASM) on RXTE. We infer that the orbit is characterized by a period Porb=250 days, a projected semimajor axis of the neutron star axsini=454 lt-s, a mass function f(M)=1.61 Msolar, and a modest eccentricity e=0.11. The measured orbital parameters, together with the known properties of the classical Be star X Per, imply a semimajor axis a=1.8-2.2 AU and an orbital inclination i~26deg-33deg. We discuss the formation of the system in the context of the standard evolutionary scenario for Be/X-ray binaries. We find that the system most likely formed from a pair of massive progenitor stars and probably involved a quasi-stable and nearly conservative transfer of mass from the primary to the secondary. We find that the He star remnant of the primary most likely had a mass probability of a system like that of X Per forming with an orbital eccentricity e<~0.11. We speculate that there may be a substantial population of neutron stars formed with little or no kick. Finally, we discuss the connected topics of the wide orbit and accretion by the neutron star from a stellar wind.

Supernova SN1961v - an explosion of a very massive star

International Nuclear Information System (INIS)

Utrobin, V.P.

1983-01-01

An investigation of the outburst of the unique supernova SN1961v in the galaxy NGC 1058 is carried out. An analysis of hydrodynamical models of supernoVa outbursts and a comparison with a considerable body of observational data on SN1961v clearly show that the SN1961v phenomenon is an explosion of a very massive star-with the mass of 2000 M and radiUs of about 100 R that results in expelling the envelope with the kinetic energy of 1.8x10 52 erg. The light curve of SN1961v furnishes direct evidence for a heterogeneity of the presupernova interior. The chemical composition produced during the evolution of the very massive star and in the final eXplosion must have a number of the essential features. In particular, hydrogen has to be underabundant relative to the solar content and distributed in the specific manner through the star. At late stages from February 1963 to February 1967, the light curve of SN1961v may be accoUnted for as interaction of the expelled envelope with the stellar wind of presupernova

How Very Massive Metal Free Stars Start Cosmological Reionization

International Nuclear Information System (INIS)

Wise, John H.; Abel, Tom

2007-01-01

The initial conditions and relevant physics for the formation of the earliest galaxies are well specified in the concordance cosmology. Using ab initio cosmological Eulerian adaptive mesh refinement radiation hydrodynamical calculations, we discuss how very massive stars start the process of cosmological reionization. The models include non-equilibrium primordial gas chemistry and cooling processes and accurate radiation transport in the Case B approximation using adaptively ray traced photon packages, retaining the time derivative in the transport equation. Supernova feedback is modeled by thermal explosions triggered at parsec scales. All calculations resolve the local Jeans length by at least 16 grid cells at all times and as such cover a spatial dynamic range of ∼10 6 . These first sources of reionization are highly intermittent and anisotropic and first photoionize the small scales voids surrounding the halos they form in, rather than the dense filaments they are embedded in. As the merging objects form larger, dwarf sized galaxies, the escape fraction of UV radiation decreases and the H II regions only break out on some sides of the galaxies making them even more anisotropic. In three cases, SN blast waves induce star formation in overdense regions that were formed earlier from ionization front instabilities. These stars form tens of parsecs away from the center of their parent DM halo. Approximately 5 ionizing photons are needed per sustained ionization when star formation in 10 6 M · halos are dominant in the calculation. As the halos become larger than ∼10 7 M # circle d ot#, the ionizing photon escape fraction decreases, which in turn increases the number of photons per ionization to 15--50, in calculations with stellar feedback only. Supernova feedback in these more massive halos creates a more diffuse medium, allowing the stellar radiation to escape more easily and maintaining the ratio of 5 ionizing photons per sustained ionization

Galactic Winds and the Role Played by Massive Stars

Science.gov (United States)

Heckman, Timothy M.; Thompson, Todd A.

Galactic winds from star-forming galaxies play at key role in the evolution of galaxies and the intergalactic medium. They transport metals out of galaxies, chemically enriching the intergalactic medium and modifying the chemical evolution of galaxies. They affect the surrounding interstellar and circumgalactic media, thereby influencing the growth of galaxies though gas accretion and star formation. In this contribution we first summarize the physical mechanisms by which the momentum and energy output from a population of massive stars and associated supernovae can drive galactic winds. We use the prototypical example of M 82 to illustrate the multiphase nature of galactic winds. We then describe how the basic properties of galactic winds are derived from the data, and summarize how the properties of galactic winds vary systematically with the properties of the galaxies that launch them. We conclude with a brief discussion of the broad implications of galactic winds.

Peering to the Heart of Massive Star Birth

Science.gov (United States)

Tan, Jonathan

2015-10-01

We propose a small survey of massive/intermediate-mass protostars with WFC3/IR to probe J and H band continuum emission, the Pa-beta and the [FeII] emission. The protostar sample is already the subject of approved SOFIA-FORCAST observations from 10-40 microns. Combined with sophisticated radiative transfer models, these observations are providing the most detailed constraints on the nature of massive protostars, their luminosities, outflow cavity structures and orientations, and distribution of surrounding dense core gas and dust. Recently, we were also awarded ALMA Cycle 3 time to study these sources at up to 0.14 resolution. The proposed HST observations, with very similar resolution, have three main goals: 1) Detect and characterize J and H band continuum emission from the massive/intermediate-mass protostars, which is expected to arise from jet and outflow knot features and from scattered light emerging from the outflow cavities; 2) Detect and characterize Pa-beta and [FeII] line emission tracing ionized and FUV-illuminated regions around the massive protostars, important diagnostics of the protostellar source and its outflow structure; 3) Search for lower-mass protostars that may be clustered around the forming massive protostar. All of these objectives will help test massive star formation theories. The high sensitivity and angular resolution of WFC3/IR enables these observations to be carried out efficiently in a timely fashion. Mid-Cycle observations are critical for near contemporaneous observation with ALMA, since jet/outflow knots may have large proper motions, and to maximize the potential time baseline for a future HST study of jet/outflow proper motions.

FRIENDS OF HOT JUPITERS. III. AN INFRARED SPECTROSCOPIC SEARCH FOR LOW-MASS STELLAR COMPANIONS

Energy Technology Data Exchange (ETDEWEB)

Piskorz, Danielle; Knutson, Heather A.; Ngo, Henry; Batygin, Konstantin [Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA (United States); Muirhead, Philip S. [Institute for Astrophysical Research, Boston University, Boston, MA (United States); Crepp, Justin R. [Department of Physics, University of Notre Dame, South Bend, IN (United States); Hinkley, Sasha [Department of Physics and Astronomy, University of Exeter, Exeter (United Kingdom); Morton, Timothy D., E-mail: dpiskorz@gps.caltech.edu [Department of Astrophysical Sciences, Princeton University, Princeton, NJ (United States)

2015-12-01

Surveys of nearby field stars indicate that stellar binaries are common, yet little is known about the effects that these companions may have on planet formation and evolution. The Friends of Hot Jupiters project uses three complementary techniques to search for stellar companions to known planet-hosting stars: radial velocity monitoring, adaptive optics imaging, and near-infrared spectroscopy. In this paper, we examine high-resolution K band infrared spectra of fifty stars hosting gas giant planets on short-period orbits. We use spectral fitting to search for blended lines due to the presence of cool stellar companions in the spectra of our target stars, where we are sensitive to companions with temperatures between 3500 and 5000 K and projected separations less than 100 AU in most systems. We identify eight systems with candidate low-mass companions, including one companion that was independently detected in our AO imaging survey. For systems with radial velocity accelerations, a spectroscopic non-detection rules out scenarios involving a stellar companion in a high inclination orbit. We use these data to place an upper limit on the stellar binary fraction at small projected separations, and show that the observed population of candidate companions is consistent with that of field stars and also with the population of wide-separation companions detected in our previous AO survey. We find no evidence that spectroscopic stellar companions are preferentially located in systems with short-period gas giant planets on eccentric and/or misaligned orbits.

FRIENDS OF HOT JUPITERS. III. AN INFRARED SPECTROSCOPIC SEARCH FOR LOW-MASS STELLAR COMPANIONS

International Nuclear Information System (INIS)

Piskorz, Danielle; Knutson, Heather A.; Ngo, Henry; Batygin, Konstantin; Muirhead, Philip S.; Crepp, Justin R.; Hinkley, Sasha; Morton, Timothy D.

2015-01-01

Surveys of nearby field stars indicate that stellar binaries are common, yet little is known about the effects that these companions may have on planet formation and evolution. The Friends of Hot Jupiters project uses three complementary techniques to search for stellar companions to known planet-hosting stars: radial velocity monitoring, adaptive optics imaging, and near-infrared spectroscopy. In this paper, we examine high-resolution K band infrared spectra of fifty stars hosting gas giant planets on short-period orbits. We use spectral fitting to search for blended lines due to the presence of cool stellar companions in the spectra of our target stars, where we are sensitive to companions with temperatures between 3500 and 5000 K and projected separations less than 100 AU in most systems. We identify eight systems with candidate low-mass companions, including one companion that was independently detected in our AO imaging survey. For systems with radial velocity accelerations, a spectroscopic non-detection rules out scenarios involving a stellar companion in a high inclination orbit. We use these data to place an upper limit on the stellar binary fraction at small projected separations, and show that the observed population of candidate companions is consistent with that of field stars and also with the population of wide-separation companions detected in our previous AO survey. We find no evidence that spectroscopic stellar companions are preferentially located in systems with short-period gas giant planets on eccentric and/or misaligned orbits

A COMPANION AS THE CAUSE OF LATITUDE-DEPENDENT EFFECTS IN THE WIND OF ETA CARINAE

International Nuclear Information System (INIS)

Groh, J. H.; Madura, T. I.; Weigelt, G.; Hillier, D. J.; Kruip, C. J. H.

2012-01-01

We analyze spatially resolved spectroscopic observations of the Eta Carinae binary system obtained with the Hubble Space Telescope/STIS. Eta Car is enshrouded by the dusty Homunculus nebula, which scatters light emitted by the central binary and provides a unique opportunity to study a massive binary system from different vantage points. We investigate the latitudinal and azimuthal dependence of Hα line profiles caused by the presence of a wind-wind collision (WWC) cavity created by the companion star. Using two-dimensional radiative transfer models, we find that the wind cavity can qualitatively explain the observed line profiles around apastron. Regions of the Homunculus which scatter light that propagated through the WWC cavity show weaker or no Hα absorption. Regions scattering light that propagated through a significant portion of the primary wind show stronger P Cygni absorption. Our models overestimate the Hα absorption formed in the primary wind, which we attribute to photoionization by the companion, not presently included in the models. We can qualitatively explain the latitudinal changes that occur during periastron, shedding light on the nature of Eta Car's spectroscopic events. Our models support the idea that during the brief period of time around periastron when the primary wind flows unimpeded toward the observer, Hα absorption occurs in directions toward the central object and Homunculus SE pole, but not toward equatorial regions close to the Weigelt blobs. We suggest that observed latitudinal and azimuthal variations are dominated by the companion star via the WWC cavity, rather than by rapid rotation of the primary star.

Asymmetric core collapse of rapidly rotating massive star

Science.gov (United States)

Gilkis, Avishai

2018-02-01

Non-axisymmetric features are found in the core collapse of a rapidly rotating massive star, which might have important implications for magnetic field amplification and production of a bipolar outflow that can explode the star, as well as for r-process nucleosynthesis and natal kicks. The collapse of an evolved rapidly rotating MZAMS = 54 M⊙ star is followed in three-dimensional hydrodynamic simulations using the FLASH code with neutrino leakage. A rotating proto-neutron star (PNS) forms with a non-zero linear velocity. This can contribute to the natal kick of the remnant compact object. The PNS is surrounded by a turbulent medium, where high shearing is likely to amplify magnetic fields, which in turn can drive a bipolar outflow. Neutron-rich material in the PNS vicinity might induce strong r-process nucleosynthesis. The rapidly rotating PNS possesses a rotational energy of E_rot ≳ 10^{52} erg. Magnetar formation proceeding in a similar fashion will be able to deposit a portion of this energy later on in the supernova ejecta through a spin-down mechanism. These processes can be important for rare supernovae generated by rapidly rotating progenitors, even though a complete explosion is not simulated in the present study.

SPITZER SAGE INFRARED PHOTOMETRY OF MASSIVE STARS IN THE LARGE MAGELLANIC CLOUD

International Nuclear Information System (INIS)

Bonanos, A. Z.; Massa, D. L.; Sewilo, M.

2009-01-01

We present a catalog of 1750 massive stars in the Large Magellanic Cloud (LMC), with accurate spectral types compiled from the literature, and a photometric catalog for a subset of 1268 of these stars, with the goal of exploring their infrared properties. The photometric catalog consists of stars with infrared counterparts in the Spitzer SAGE survey database, for which we present uniform photometry from 0.3 to 24 μm in the UBVIJHK s +IRAC+MIPS24 bands. The resulting infrared color-magnitude diagrams illustrate that the supergiant B[e], red supergiant, and luminous blue variable (LBV) stars are among the brightest infrared point sources in the LMC, due to their intrinsic brightness, and at longer wavelengths, due to dust. We detect infrared excesses due to free-free emission among ∼900 OB stars, which correlate with luminosity class. We confirm the presence of dust around 10 supergiant B[e] stars, finding the shape of their spectral energy distributions (SEDs) to be very similar, in contrast to the variety of SED shapes among the spectrally variable LBVs. The similar luminosities of B[e] supergiants (log L/L sun ≥ 4) and the rare, dusty progenitors of the new class of optical transients (e.g., SN 2008S and NGC 300 OT), plus the fact that dust is present in both types of objects, suggests a common origin for them. We find the infrared colors for Wolf-Rayet stars to be independent of spectral type and their SEDs to be flatter than what models predict. The results of this study provide the first comprehensive roadmap for interpreting luminous, massive, resolved stellar populations in nearby galaxies at infrared wavelengths.

Global and radial variations in the efficiency of massive star formation among galaxies

International Nuclear Information System (INIS)

Allen, L.E.; Young, J.S.

1990-01-01

In order to determine the regions within galaxies which give rise to the most efficient star formation and to test the hypothesis that galaxies with high infrared luminosities per unit molecular mass are efficiently producing high mass stars, researchers have undertaken an H alpha imaging survey in galaxies whose CO distributions have been measured as part of the Five College Radio Astronomy Observatory (FCRAO) Extragalactic CO Survey. From these images researchers have derived global H alpha fluxes and distributions for comparison with far infrared radiation (FIR) fluxes and CO fluxes and distributions. Here, researchers present results on the global massive star formation efficiency (SFE = L sub H sub alpha/M(H2)) as a function of morphological type and environment, and on the radial distribution of the SFE within both peculiar and isolated galaxies. On the basis of comparison of the global L sub H sub alpha/M(H2) and L sub FIR/M(H2) for 111 galaxies, researchers conclude that environment rather than morphological type has the strongest effect on the global efficiency of massive star formation. Based on their study of a small sample, they find that the largest radial gradients are observed in the interacting/peculiar galaxies, indicating that environment affects the star formation efficiency within galaxies as well

RESOLVED COMPANIONS OF CEPHEIDS: TESTING THE CANDIDATES WITH X-RAY OBSERVATIONS

Energy Technology Data Exchange (ETDEWEB)

Evans, Nancy Remage; Pillitteri, Ignazio; Wolk, Scott; Karovska, Margarita; Tingle, Evan [Smithsonian Astrophysical Observatory, MS 4, 60 Garden St., Cambridge, MA 02138 (United States); Guinan, Edward; Engle, Scott [Department of Astronomy and Astrophysics, Villanova University, 800 Lancaster Ave., Villanova, PA 19085 (United States); Bond, Howard E. [Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802 (United States); Schaefer, Gail H. [The CHARA Array of Georgia State University, Mount Wilson, California 91023 (United States); Mason, Brian D., E-mail: nevans@cfa.harvard.edu, E-mail: heb11@psu.edu, E-mail: schaefer@chara-array.org [US Naval Observatory, 3450 Massachusetts Ave., NW, Washington, DC 20392-5420 (United States)

2016-04-15

We have made XMM-Newton observations of 14 Galactic Cepheids that have candidate resolved (≥5″) companion stars based on our earlier HST Wide Field Camera 3 (WFC3) imaging survey. Main-sequence stars that are young enough to be physical companions of Cepheids are expected to be strong X-ray producers in contrast to field stars. XMM-Newton exposures were set to detect essentially all companions hotter than spectral type M0 (corresponding to 0.5 M{sub ⊙}). The large majority of our candidate companions were not detected in X-rays, and hence are not confirmed as young companions. One resolved candidate (S Nor #4) was unambiguously detected, but the Cepheid is a member of a populous cluster. For this reason, it is likely that S Nor #4 is a cluster member rather than a gravitationally bound companion. Two further Cepheids (S Mus and R Cru) have X-ray emission that might be produced by either the Cepheid or the candidate resolved companion. A subsequent Chandra observation of S Mus shows that the X-rays are at the location of the Cepheid/spectroscopic binary. R Cru and also V659 Cen (also X-ray bright) have possible companions closer than 5″ (the limit for this study) which are the likely sources of X-rays. One final X-ray detection (V473 Lyr) has no known optical companion, so the prime suspect is the Cepheid itself. It is a unique Cepheid with a variable amplitude. The 14 stars that we observed with XMM constitute 36% of the 39 Cepheids found to have candidate companions in our HST/WFC3 optical survey. No young probable binary companions were found with separations of ≥5″ or 4000 au.

RESOLVED COMPANIONS OF CEPHEIDS: TESTING THE CANDIDATES WITH X-RAY OBSERVATIONS

International Nuclear Information System (INIS)

Evans, Nancy Remage; Pillitteri, Ignazio; Wolk, Scott; Karovska, Margarita; Tingle, Evan; Guinan, Edward; Engle, Scott; Bond, Howard E.; Schaefer, Gail H.; Mason, Brian D.

2016-01-01

We have made XMM-Newton observations of 14 Galactic Cepheids that have candidate resolved (≥5″) companion stars based on our earlier HST Wide Field Camera 3 (WFC3) imaging survey. Main-sequence stars that are young enough to be physical companions of Cepheids are expected to be strong X-ray producers in contrast to field stars. XMM-Newton exposures were set to detect essentially all companions hotter than spectral type M0 (corresponding to 0.5 M ⊙ ). The large majority of our candidate companions were not detected in X-rays, and hence are not confirmed as young companions. One resolved candidate (S Nor #4) was unambiguously detected, but the Cepheid is a member of a populous cluster. For this reason, it is likely that S Nor #4 is a cluster member rather than a gravitationally bound companion. Two further Cepheids (S Mus and R Cru) have X-ray emission that might be produced by either the Cepheid or the candidate resolved companion. A subsequent Chandra observation of S Mus shows that the X-rays are at the location of the Cepheid/spectroscopic binary. R Cru and also V659 Cen (also X-ray bright) have possible companions closer than 5″ (the limit for this study) which are the likely sources of X-rays. One final X-ray detection (V473 Lyr) has no known optical companion, so the prime suspect is the Cepheid itself. It is a unique Cepheid with a variable amplitude. The 14 stars that we observed with XMM constitute 36% of the 39 Cepheids found to have candidate companions in our HST/WFC3 optical survey. No young probable binary companions were found with separations of ≥5″ or 4000 au

Chemical evolution with rotating massive star yields - I. The solar neighbourhood and the s-process elements

Science.gov (United States)

Prantzos, N.; Abia, C.; Limongi, M.; Chieffi, A.; Cristallo, S.

2018-05-01

We present a comprehensive study of the abundance evolution of the elements from H to U in the Milky Way halo and local disc. We use a consistent chemical evolution model, metallicity-dependent isotopic yields from low and intermediate mass stars and yields from massive stars which include, for the first time, the combined effect of metallicity, mass loss, and rotation for a large grid of stellar masses and for all stages of stellar evolution. The yields of massive stars are weighted by a metallicity-dependent function of the rotational velocities, constrained by observations as to obtain a primary-like 14N behaviour at low metallicity and to avoid overproduction of s-elements at intermediate metallicities. We show that the Solar system isotopic composition can be reproduced to better than a factor of 2 for isotopes up to the Fe-peak, and at the 10 per cent level for most pure s-isotopes, both light ones (resulting from the weak s-process in rotating massive stars) and the heavy ones (resulting from the main s-process in low and intermediate mass stars). We conclude that the light element primary process (LEPP), invoked to explain the apparent abundance deficiency of the s-elements with A values of ^{12}C/^{13}C in halo red giants, which is rather due to internal processes in those stars.

An infrared view of (candidate accretion) disks around massive young stars

NARCIS (Netherlands)

Bik, A.; Lenorzer, A.; Thi, W.F.; Puga Antolín, E.; Waters, L.B.F.M.; Kaper, L.; Martín-Hernández, L.N.

2008-01-01

Near-infrared surveys of high-mass star-forming regions start to shed light onto their stellar content. A particular class of objects found in these regions, the so-called massive Young Stellar Objects (YSOs) are surrounded by dense circumstellar material. Several near- and mid-infrared diagnostic

Massive open star clusters using the VVV survey. II. Discovery of six clusters with Wolf-Rayet stars

Science.gov (United States)

Chené, A.-N.; Borissova, J.; Bonatto, C.; Majaess, D. J.; Baume, G.; Clarke, J. R. A.; Kurtev, R.; Schnurr, O.; Bouret, J.-C.; Catelan, M.; Emerson, J. P.; Feinstein, C.; Geisler, D.; de Grijs, R.; Hervé, A.; Ivanov, V. D.; Kumar, M. S. N.; Lucas, P.; Mahy, L.; Martins, F.; Mauro, F.; Minniti, D.; Moni Bidin, C.

2013-01-01

Context. The ESO Public Survey "VISTA Variables in the Vía Láctea" (VVV) provides deep multi-epoch infrared observations for an unprecedented 562 sq. degrees of the Galactic bulge, and adjacent regions of the disk. Nearly 150 new open clusters and cluster candidates have been discovered in this survey. Aims: This is the second in a series of papers about young, massive open clusters observed using the VVV survey. We present the first study of six recently discovered clusters. These clusters contain at least one newly discovered Wolf-Rayet (WR) star. Methods: Following the methodology presented in the first paper of the series, wide-field, deep JHKs VVV observations, combined with new infrared spectroscopy, are employed to constrain fundamental parameters for a subset of clusters. Results: We find that the six studied stellar groups are real young (2-7 Myr) and massive (between 0.8 and 2.2 × 103 M⊙) clusters. They are highly obscured (AV ~ 5-24 mag) and compact (1-2 pc). In addition to WR stars, two of the six clusters also contain at least one red supergiant star, and one of these two clusters also contains a blue supergiant. We claim the discovery of 8 new WR stars, and 3 stars showing WR-like emission lines which could be classified WR or OIf. Preliminary analysis provides initial masses of ~30-50 M⊙ for the WR stars. Finally, we discuss the spiral structure of the Galaxy using the six new clusters as tracers, together with the previously studied VVV clusters. Based on observations with ISAAC, VLT, ESO (programme 087.D-0341A), New Technology Telescope at ESO's La Silla Observatory (programme 087.D-0490A) and with the Clay telescope at the Las Campanas Observatory (programme CN2011A-086). Also based on data from the VVV survey (programme 172.B-2002).

LOW-MASS VISUAL COMPANIONS TO NEARBY G-DWARFS

International Nuclear Information System (INIS)

Tokovinin, Andrei

2011-01-01

A complete census of wide visual companions to nearby G-dwarf stars can be achieved by selecting candidates from the Two Micron All Sky Survey (2MASS) Point-Source Catalog and checking their status by second-epoch imaging. Such data are obtained for 124 candidates with separations up to 20'', 47 of which are shown to be new physical low-mass stellar companions. A list of visual binaries with G-dwarf primaries is produced by combining newly found companions with historical data. Maximum likelihood analysis leads to a companion frequency of 0.13 ± 0.015 per decade of separation. The mass ratio is distributed almost uniformly, with a power-law index between -0.4 and 0. The remaining uncertainty in the index is related to modeling of the companion detection threshold in 2MASS. These findings are confirmed by an alternative analysis of wider companions in 2MASS, removing the contamination by background stars statistically. Extension of this work will lead to a complete detection of visual companions-a necessary step toward reaching unbiased multiplicity statistics over the full range of orbital periods and, eventually, understanding the origin of multiple systems.

The secular tidal disruption of stars by low-mass Super Massive Black Holes secondaries in galactic nuclei

Science.gov (United States)

Fragione, Giacomo; Leigh, Nathan

2018-06-01

Stars passing too close to a super massive black hole (SMBH) can produce tidal disruption events (TDEs). Since the resulting stellar debris can produce an electromagnetic flare, TDEs are believed to probe the presence of single SMBHs in galactic nuclei, which otherwise remain dark. In this paper, we show how stars orbiting an IMBH secondary are perturbed by an SMBH primary. We find that the evolution of the stellar orbits are severely affected by the primary SMBH due to secular effects and stars orbiting with high inclinations with respect to the SMBH-IMBH orbital plane end their lives as TDEs due to Kozai-Lidov oscillations, hence illuminating the secondary SMBH/IMBH. Above a critical SMBH mass of ≈1.15 × 108 M⊙, no TDE can occur for typical stars in an old stellar population since the Schwarzschild radius exceeds the tidal disruption radius. Consequently, any TDEs due to such massive SMBHs will remain dark. It follows that no TDEs should be observed in galaxies more massive than ≈4.15 × 1010 M⊙, unless a lower-mass secondary SMBH or IMBH is also present. The secular mechanism for producing TDEs considered here therefore offers a useful probe of SMBH-SMBH/IMBH binarity in the most massive galaxies. We further show that the TDE rate can be ≈10-4 - 10-3 yr-1, and that most TDEs occur on ≈0.5 Myr. Finally, we show that stars may be ejected with velocities up to thousands of km s-1, which could contribute to the observed population of Galactic hypervelocity stars.

Stationary bound-state massive scalar field configurations supported by spherically symmetric compact reflecting stars

Energy Technology Data Exchange (ETDEWEB)

Hod, Shahar [The Ruppin Academic Center, Emeq Hefer (Israel); The Hadassah Academic College, Jerusalem (Israel)

2017-12-15

It has recently been demonstrated that asymptotically flat neutral reflecting stars are characterized by an intriguing no-hair property. In particular, it has been proved that these horizonless compact objects cannot support spatially regular static matter configurations made of scalar (spin-0) fields, vector (spin-1) fields and tensor (spin-2) fields. In the present paper we shall explicitly prove that spherically symmetric compact reflecting stars can support stationary (rather than static) bound-state massive scalar fields in their exterior spacetime regions. To this end, we solve analytically the Klein-Gordon wave equation for a linearized scalar field of mass μ and proper frequency ω in the curved background of a spherically symmetric compact reflecting star of mass M and radius R{sub s}. It is proved that the regime of existence of these stationary composed star-field configurations is characterized by the simple inequalities 1 - 2M/R{sub s} < (ω/μ){sup 2} < 1. Interestingly, in the regime M/R{sub s} << 1 of weakly self-gravitating stars we derive a remarkably compact analytical equation for the discrete spectrum {ω(M,R_s, μ)}{sup n=∞}{sub n=1} of resonant oscillation frequencies which characterize the stationary composed compact-reflecting-star-linearized-massive-scalar-field configurations. Finally, we verify the accuracy of the analytically derived resonance formula of the composed star-field configurations with direct numerical computations. (orig.)

A parsec-scale optical jet from a massive young star in the Large Magellanic Cloud.

Science.gov (United States)

McLeod, Anna F; Reiter, Megan; Kuiper, Rolf; Klaassen, Pamela D; Evans, Christopher J

2018-02-15

Highly collimated parsec-scale jets, which are generally linked to the presence of an accretion disk, are commonly observed in low-mass young stellar objects. In the past two decades, a few of these jets have been directly (or indirectly) observed from higher-mass (larger than eight solar masses) young stellar objects, adding to the growing evidence that disk-mediated accretion also occurs in high-mass stars, the formation mechanism of which is still poorly understood. Of the observed jets from massive young stars, none is in the optical regime (massive young stars are typically highly obscured by their natal material), and none is found outside of the Milky Way. Here we report observations of HH 1177, an optical ionized jet that originates from a massive young stellar object located in the Large Magellanic Cloud. The jet is highly collimated over its entire measured length of at least ten parsecs and has a bipolar geometry. The presence of a jet indicates ongoing, disk-mediated accretion and, together with the high degree of collimation, implies that this system is probably formed through a scaled-up version of the formation mechanism of low-mass stars. We conclude that the physics that govern jet launching and collimation is independent of stellar mass.

A parsec-scale optical jet from a massive young star in the Large Magellanic Cloud

Science.gov (United States)

McLeod, Anna F.; Reiter, Megan; Kuiper, Rolf; Klaassen, Pamela D.; Evans, Christopher J.

2018-02-01

Highly collimated parsec-scale jets, which are generally linked to the presence of an accretion disk, are commonly observed in low-mass young stellar objects. In the past two decades, a few of these jets have been directly (or indirectly) observed from higher-mass (larger than eight solar masses) young stellar objects, adding to the growing evidence that disk-mediated accretion also occurs in high-mass stars, the formation mechanism of which is still poorly understood. Of the observed jets from massive young stars, none is in the optical regime (massive young stars are typically highly obscured by their natal material), and none is found outside of the Milky Way. Here we report observations of HH 1177, an optical ionized jet that originates from a massive young stellar object located in the Large Magellanic Cloud. The jet is highly collimated over its entire measured length of at least ten parsecs and has a bipolar geometry. The presence of a jet indicates ongoing, disk-mediated accretion and, together with the high degree of collimation, implies that this system is probably formed through a scaled-up version of the formation mechanism of low-mass stars. We conclude that the physics that govern jet launching and collimation is independent of stellar mass.

The little-studied cluster Berkeley 90. I. LS III +46 11: a very massive O3.5 If* + O3.5 If* binary

Science.gov (United States)

Maíz Apellániz, J.; Negueruela, I.; Barbá, R. H.; Walborn, N. R.; Pellerin, A.; Simón-Díaz, S.; Sota, A.; Marco, A.; Alonso-Santiago, J.; Sanchez Bermudez, J.; Gamen, R. C.; Lorenzo, J.

2015-07-01

Context. It appears that most (if not all) massive stars are born in multiple systems. At the same time, the most massive binaries are hard to find owing to their low numbers throughout the Galaxy and the implied large distances and extinctions. Aims: We want to study LS III +46 11, identified in this paper as a very massive binary; another nearby massive system, LS III +46 12; and the surrounding stellar cluster, Berkeley 90. Methods: Most of the data used in this paper are multi-epoch high S/N optical spectra, although we also use Lucky Imaging and archival photometry. The spectra are reduced with dedicated pipelines and processed with our own software, such as a spectroscopic-orbit code, CHORIZOS, and MGB. Results: LS III +46 11 is identified as a new very early O-type spectroscopic binary [O3.5 If* + O3.5 If*] and LS III +46 12 as another early O-type system [O4.5 V((f))]. We measure a 97.2-day period for LS III +46 11 and derive minimum masses of 38.80 ± 0.83 M⊙ and 35.60 ± 0.77 M⊙ for its two stars. We measure the extinction to both stars, estimate the distance, search for optical companions, and study the surrounding cluster. In doing so, a variable extinction is found as well as discrepant results for the distance. We discuss possible explanations and suggest that LS III +46 12 may be a hidden binary system where the companion is currently undetected.

Convective shells and the core He-burning phase of massive stars

Energy Technology Data Exchange (ETDEWEB)

Chiosi, C [Padua Univ. (Italy). Ist. di Astronomia; Nasi, E [Osservatorio Astronomico, Padova, Italy

1978-07-01

In this paper the effect of complete homogenization in the intermediate unstable layers of massive stars is briefly discussed on the effective temperature of the core He-burning models. To this end, a 20 solar masses star of Population I chemical composition (X=0.700, Z=0.020) has been allowed to evolve from the Main Sequence into the core He-exhaustion stage without taking into account semiconvective mixing. The results show that the models are systematically bluer than those computed with the same physical parameters but with the inclusion of semiconvection.

The onset of massive star formation: The evolution of temperature and density structure in an infrared dark cloud

Energy Technology Data Exchange (ETDEWEB)

Battersby, Cara [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Ginsburg, Adam; Bally, John; Darling, Jeremy [Center for Astrophysics and Space Astronomy, University of Colorado, UCB 389, Boulder, CO 80309 (United States); Longmore, Steve [Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead CH41 1LD (United Kingdom); Dunham, Miranda [Department of Astronomy, Yale University, New Haven, CT 06520 (United States)

2014-06-01

We present new NH{sub 3} (1, 1), (2, 2), and (4, 4) observations from the Karl G. Jansky Very Large Array compiled with work in the literature to explore the range of conditions observed in young, massive star-forming regions. To sample the effects of evolution independent from those of distance/resolution, abundance, and large-scale environment, we compare clumps in different evolutionary stages within a single infrared dark cloud (IRDC), G32.02+0.06. We find that the early stages of clustered star formation are characterized by dense, parsec-scale filamentary structures interspersed with complexes of dense cores (<0.1 pc cores clustered in complexes separated by ∼1 pc) with masses from about 10 to 100 M {sub ☉}. The most quiescent core is the most extended while the star forming cores are denser and more compact, showing very similar column density structure before and shortly after the onset of massive star formation, with peak surface densities Σ ≳ 1 g cm{sup –2}. Quiescent cores and filaments show smoothly varying temperatures from 10 to 20 K, rising to over 40 K in star-forming cores. We calculate virial parameters for 16 cores and find that the level of support provided by turbulence is generally insufficient to support them against gravitational collapse ((α{sub vir}) ∼ 0.6). The star-forming filaments show smooth velocity fields, punctuated by discontinuities at the sites of active star formation. We discuss the massive molecular filament (M ∼ 10{sup 5} M {sub ☉}, length >60 pc) hosting the IRDC, hypothesizing that it may have been shaped by previous generations of massive stars.

Massive open star clusters using the VVV survey IV. WR 62-2, a new very massive star in the core of the VVV CL041 cluster

Czech Academy of Sciences Publication Activity Database

Chene, A.-N.; Alegria, S.R.; Borissova, J.; O'Leary, E.; Martins, F.; Hervé, Anthony; Kuhn, M.; Kurtev, R.; Consuelo Amigo Fuentes, P.; Bonatto, C.; Minniti, D.

2015-01-01

Roč. 584, December (2015), A31/1-A31/8 ISSN 0004-6361 R&D Projects: GA ČR(CZ) GA14-02385S Institutional support: RVO:67985815 Keywords : open clusters and associations * VVV CL041 * massive star s Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.378, year: 2014

OBSERVATIONS OF BINARY STARS WITH THE DIFFERENTIAL SPECKLE SURVEY INSTRUMENT. V. TOWARD AN EMPIRICAL METAL-POOR MASS–LUMINOSITY RELATION

International Nuclear Information System (INIS)

Horch, Elliott P.; Van Altena, William F.; Demarque, Pierre; Howell, Steve B.; Everett, Mark E.; Ciardi, David R.; Teske, Johanna K.; Henry, Todd J.; Winters, Jennifer G.

2015-01-01

In an effort to better understand the details of the stellar structure and evolution of metal-poor stars, the Gemini North telescope was used on two occasions to take speckle imaging data of a sample of known spectroscopic binary stars and other nearby stars in order to search for and resolve close companions. The observations were obtained using the Differential Speckle Survey Instrument, which takes data in two filters simultaneously. The results presented here are of 90 observations of 23 systems in which one or more companions was detected, and six stars where no companion was detected to the limit of the camera capabilities at Gemini. In the case of the binary and multiple stars, these results are then further analyzed to make first orbit determinations in five cases, and orbit refinements in four other cases. The mass information is derived, and since the systems span a range in metallicity, a study is presented that compares our results with the expected trend in total mass as derived from the most recent Yale isochrones as a function of metal abundance. These data suggest that metal-poor main-sequence stars are less massive at a given color than their solar-metallicity analogues in a manner consistent with that predicted from the theory

Polarized bow shocks reveal features of the winds and environments of massive stars

Science.gov (United States)

Shrestha, Manisha

2018-01-01

Massive stars strongly affect their surroundings through their energetic stellar winds and deaths as supernovae. The bow shock structures created by fast-moving massive stars contain important information about the winds and ultimate fates of these stars as well as their local interstellar medium (ISM). Since bow shocks are aspherical, the light scattered in the dense shock material becomes polarized. Analyzing this polarization reveals details of the bow shock geometry as well as the composition, velocity, density, and albedo of the scattering material. With these quantities, we can constrain the properties of the stellar wind and thus the evolutionary state of the star, as well as the dust composition of the local ISM.In my dissertation research, I use a Monte Carlo radiative transfer code that I optimized to simulate the polarization signatures produced by both resolved and unresolved stellar wind bow shocks (SWBS) illuminated by a central star and by shock emission. I derive bow shock shapes and densities from published analytical calculations and smooth particle hydrodynamic (SPH) models. In the case of the analytical SWBS and electron scattering, I find that higher optical depths produce higher polarization and position angle rotations at specific viewing angles compared to theoretical predictions for low optical depths. This is due to the geometrical properties of the bow shock combined with multiple scattering effects. For dust scattering, the polarization signature is strongly affected by wavelength, dust grain properties, and viewing angle. The behavior of the polarization as a function of wavelength in these cases can distinguish among different dust models for the local ISM. In the case of SPH density structures, I investigate how the polarization changes as a function of the evolutionary phase of the SWBS. My dissertation compares these simulations with polarization data from Betelgeuse and other massive stars with bow shocks. I discuss the

Ionizing feedback from massive stars in massive clusters - III. Disruption of partially unbound clouds

Science.gov (United States)

Dale, J. E.; Ercolano, B.; Bonnell, I. A.

2013-03-01

We extend our previous smoothed particle hydrodynamics parameter study of the effects of photoionization from O-stars on star-forming clouds to include initially unbound clouds. We generate a set of model clouds in the mass range 104-106 M⊙ with initial virial ratios Ekin/Epot = 2.3, allow them to form stars and study the impact of the photoionizing radiation produced by the massive stars. We find that, on the 3 Myr time-scale before supernovae are expected to begin detonating, the fraction of mass expelled by ionizing feedback is a very strong function of the cloud escape velocities. High-mass clouds are largely unaffected dynamically, while low-mass clouds have large fractions of their gas reserves expelled on this time-scale. However, the fractions of stellar mass unbound are modest and significant portions of the unbound stars are so only because the clouds themselves are initially partially unbound. We find that ionization is much more able to create well-cleared bubbles in the unbound clouds, owing to their intrinsic expansion, but that the presence of such bubbles does not necessarily indicate that a given cloud has been strongly influenced by feedback. We also find, in common with the bound clouds from our earlier work, that many of the systems simulated here are highly porous to photons and supernova ejecta, and that most of them will likely survive their first supernova explosions.

Friends of hot Jupiters. I. A radial velocity search for massive, long-period companions to close-in gas giant planets

Energy Technology Data Exchange (ETDEWEB)

Knutson, Heather A.; Ngo, Henry; Johnson, John Asher [Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 (United States); Fulton, Benjamin J.; Howard, Andrew W. [Institute for Astronomy, University of Hawaii at Manoa, Honolulu, HI (United States); Montet, Benjamin T.; Kao, Melodie; Hinkley, Sasha; Morton, Timothy D.; Muirhead, Philip S. [Cahill Center for Astronomy and Astrophysics, California Institute of Technology, 1200 East California Boulevard, MC 249-17, Pasadena, CA 91125 (United States); Crepp, Justin R. [Department of Physics, University of Notre Dame, Notre Dame, IN (United States); Bakos, Gaspar Á. [Department of Astrophysical Sciences, Princeton University, Princeton, NJ (United States); Batygin, Konstantin, E-mail: hknutson@caltech.edu [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States)

2014-04-20

In this paper we search for distant massive companions to known transiting gas giant planets that may have influenced the dynamical evolution of these systems. We present new radial velocity observations for a sample of 51 planets obtained using the Keck HIRES instrument, and find statistically significant accelerations in fifteen systems. Six of these systems have no previously reported accelerations in the published literature: HAT-P-10, HAT-P-22, HAT-P-29, HAT-P-32, WASP-10, and XO-2. We combine our radial velocity fits with Keck NIRC2 adaptive optics (AO) imaging data to place constraints on the allowed masses and orbital periods of the companions responsible for the detected accelerations. The estimated masses of the companions range between 1-500 M {sub Jup}, with orbital semi-major axes typically between 1-75 AU. A significant majority of the companions detected by our survey are constrained to have minimum masses comparable to or larger than those of the transiting planets in these systems, making them candidates for influencing the orbital evolution of the inner gas giant. We estimate a total occurrence rate of 51% ± 10% for companions with masses between 1-13 M {sub Jup} and orbital semi-major axes between 1-20 AU in our sample. We find no statistically significant difference between the frequency of companions to transiting planets with misaligned or eccentric orbits and those with well-aligned, circular orbits. We combine our expanded sample of radial velocity measurements with constraints from transit and secondary eclipse observations to provide improved measurements of the physical and orbital characteristics of all of the planets included in our survey.

A massive, dead disk galaxy in the early Universe.

Science.gov (United States)

Toft, Sune; Zabl, Johannes; Richard, Johan; Gallazzi, Anna; Zibetti, Stefano; Prescott, Moire; Grillo, Claudio; Man, Allison W S; Lee, Nicholas Y; Gómez-Guijarro, Carlos; Stockmann, Mikkel; Magdis, Georgios; Steinhardt, Charles L

2017-06-21

At redshift z = 2, when the Universe was just three billion years old, half of the most massive galaxies were extremely compact and had already exhausted their fuel for star formation. It is believed that they were formed in intense nuclear starbursts and that they ultimately grew into the most massive local elliptical galaxies seen today, through mergers with minor companions, but validating this picture requires higher-resolution observations of their centres than is currently possible. Magnification from gravitational lensing offers an opportunity to resolve the inner regions of galaxies. Here we report an analysis of the stellar populations and kinematics of a lensed z = 2.1478 compact galaxy, which-surprisingly-turns out to be a fast-spinning, rotationally supported disk galaxy. Its stars must have formed in a disk, rather than in a merger-driven nuclear starburst. The galaxy was probably fed by streams of cold gas, which were able to penetrate the hot halo gas until they were cut off by shock heating from the dark matter halo. This result confirms previous indirect indications that the first galaxies to cease star formation must have gone through major changes not just in their structure, but also in their kinematics, to evolve into present-day elliptical galaxies.

THE ABSENCE OF EX-COMPANIONS IN TYPE Ia SUPERNOVA REMNANTS

Energy Technology Data Exchange (ETDEWEB)

Di Stefano, R. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Kilic, Mukremin, E-mail: rd@cfa.harvard.edu, E-mail: kilic@ou.edu [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 West Brooks Street, Norman, OK 73019 (United States)

2012-11-01

Type Ia supernovae (SNe Ia) play important roles in our study of the expansion and acceleration of the universe, but because we do not know the exact nature or natures of the progenitors, there is a systematic uncertainty that must be resolved if SNe Ia are to become more precise cosmic probes. No progenitor system has ever been identified either in the pre- or post-explosion images of a Ia event. There have been recent claims for and against the detection of ex-companion stars in several SNe Ia remnants. These studies, however, usually ignore the angular momentum gain of the progenitor white dwarf (WD), which leads to a spin-up phase and a subsequent spin-down phase before explosion. For spin-down timescales greater than 10{sup 5} years, the donor star could be too dim to detect by the time of explosion. Here we revisit the current limits on ex-companion stars to SNR 0509-67.5, a 400-year-old remnant in the Large Magellanic Cloud. If the effects of possible angular momentum gain on the WD are included, a wide range of single-degenerate progenitor models are allowed for this remnant. We demonstrate that the current absence of evidence for ex-companion stars in this remnant, as well as other SNe Ia remnants, does not necessarily provide the evidence of absence for ex-companions. We discuss potential ways to identify such ex-companion stars through deep imaging observations.

THE ABSENCE OF EX-COMPANIONS IN TYPE Ia SUPERNOVA REMNANTS

International Nuclear Information System (INIS)

Di Stefano, R.; Kilic, Mukremin

2012-01-01

Type Ia supernovae (SNe Ia) play important roles in our study of the expansion and acceleration of the universe, but because we do not know the exact nature or natures of the progenitors, there is a systematic uncertainty that must be resolved if SNe Ia are to become more precise cosmic probes. No progenitor system has ever been identified either in the pre- or post-explosion images of a Ia event. There have been recent claims for and against the detection of ex-companion stars in several SNe Ia remnants. These studies, however, usually ignore the angular momentum gain of the progenitor white dwarf (WD), which leads to a spin-up phase and a subsequent spin-down phase before explosion. For spin-down timescales greater than 10 5 years, the donor star could be too dim to detect by the time of explosion. Here we revisit the current limits on ex-companion stars to SNR 0509-67.5, a 400-year-old remnant in the Large Magellanic Cloud. If the effects of possible angular momentum gain on the WD are included, a wide range of single-degenerate progenitor models are allowed for this remnant. We demonstrate that the current absence of evidence for ex-companion stars in this remnant, as well as other SNe Ia remnants, does not necessarily provide the evidence of absence for ex-companions. We discuss potential ways to identify such ex-companion stars through deep imaging observations.

On the signatures of companion formation in the spectral energy distributions of Sz54 and Sz59—the young stars with protoplanetary disks

Science.gov (United States)

Zakhozhay, O. V.

2017-07-01

We study spectral energy distributions of two young systems Sz54 and Sz59, that belong to Chameleon II star forming region. The results of the modeling indicate that protoplanetary disks of these systems contain gaps in the dust component. These gaps could be a result of a planetary or brown dwarf companion formation, because the companion would accumulate a disk material, moving along its orbit. In a present work we have determined physical characteristics of the disks. We also discuss possible companion characteristics, based on the geometrical parameters of the gaps.

The Stars behind the Curtain

Science.gov (United States)

2010-02-01

still growing into stars, newborn stars, adult stars and stars nearing the end of their life. All these stars have roughly the same age, a million years, a blink of an eye compared to our five billion year-old Sun and Solar System. The fact that some of the stars have just started their lives while others are already dying is due to their extraordinary range of masses: high-mass stars, being very bright and hot, burn through their existence much faster than their less massive, fainter and cooler counterparts. The newly released image, obtained with the FORS instrument attached to the VLT at Cerro Paranal, Chile, portrays a wide field around the stellar cluster and reveals the rich texture of the surrounding clouds of gas and dust. Notes [1] The star, NGC 3603-A1, is an eclipsing system of two stars orbiting around each other in 3.77 days. The most massive star has an estimated mass of 116 solar masses, while its companion has a mass of 89 solar masses. More information ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world's most productive astronomical observatory. It is supported by 14 countries: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world's most advanced visible-light astronomical observatory and VISTA, the largest survey telescope. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in

Massive stars dying alone: Extremely remote environments of SN2009ip and SN2010jp

Science.gov (United States)

Smith, Nathan

2014-10-01

We propose an imaging study of the astonishingly remote environments of two recent supernovae (SNe): SN2009ip and SN2010jp. Both were unusual Type IIn explosions that crashed into dense circumstellar material (CSM) ejected by the star shortly before explosion. The favored progenitors of these SNe are very massive luminous blue variable (LBV) stars. In fact, SN2009ip presents an extraordinay case where the LBV-like progenitor was actually detected directly in archival HST data, and where we obtained spectra and photometry for numerous pre-SN eruptions. No other SN has this treasure trove of detailed information about the progenitor (not even SN1987A). SN2010jp represents a possible collapsar-powered event, since it showed evidence of a fast bipolar jet in spectra and a low 56Ni mass; this would be an analog of the black-hole forming explosions that cause gamma ray bursts, but where the relativistic jet is damped by a residual H envelope on the star. In both cases, the only viable models for these SNe involve extremely massive (initial masses of 40-100 Msun) progenitor stars. This seems at odds with their extremely remote environments in the far outskirts of their host galaxies, with no detected evidence for an underlying massive star population in ground-based data (nor in the single shallow WFPC2/F606W image of SN2009ip). Here we propose deep UV HST images to search for any mid/late O-type stars nearby, deep red images to detect any red supergiants, and an H-alpha image to search for any evidence of ongoing star formation in the vicinity. These observations will place important and demanding constraints on the initial masses and ages of these progenitors.

WO-Type Wolf-Rayet Stars: the Last Hurrah of the Most Massive Stars?

Science.gov (United States)

Massey, Philip

2014-10-01

WO-type Wolf-Rayet (WR) stars are considered the final evolutionary stage of the highest mass stars, immediate precursors to Type Ic (He-poor) core-collapse supernovae. These WO stars are rare, and until recently only 6 were known. Our knowledge about their physical properties is mostly based on a single object, Sand 2 in the LMC. It was the only non-binary WO star both bright and unreddened enough that its FUV and NUV spectra could be obtained by FUSE and HST/FOS. A non-LTE analysis showed that Sand 2 is very hot and its (C+O)/He abundance ratio is higher than that found in WC-type WRs, suggesting it is indeed highly evolved. However, the O VI resonance doublet in the FUV required a considerably cooler temperature (120,000 K) model than did the optical O VI lines (170,000 K). Further, the enhanced chemical abundances did not match the predictions of stellar evolutionary models. Another non-LTE study found a 3x higher (C+O)/He abundance ratio and a cooler temperature. We have recently discovered two other bright, single, and lightly reddened WOs in the LMC, allowing us to take a fresh look at these important objects. Our newly found WOs span a range in excitation type, from WO1 (the highest) to WO4 (the lowest). Sand 2 is intermediate (WO3). We propose to use COS to obtain FUV and NUV data of all three stars for as comprehensive a study as is currently possible. These UV data will be combined with our optical Magellan spectra for a detailed analysis with CMFGEN with the latest atomic data. Knowing the degree of chemical evolution of these WO stars is crucial to determining their evolutionary status, and thus in understanding the final stages of the most massive stars.

Water in massive star-forming regions with Herschel Space Observatory

Science.gov (United States)

Chavarria, L.; Herpin, F.; Bontemps, S.; Jacq, T.; Baudry, A.; Braine, J.; van der Tak, F.; Wyrowski, F.; van Dishoeck, E. F.

2011-05-01

High-mass stars formation process is much less understood than the low-mass case: short timescales, high opacities and long distance to the sources challenge the study of young massive stars. The instruments on board the Heschel Space Observatory permit us to investigate molecular species at high spectral resolution in the sub-milimeter wavelengths. Water, one of the most abundant molecules in the Universe, might elucidate key episodes in the process of stellar birth and it may play a major role in the formation of high-mass stars. This contribution presents the first results of the Heschel Space Observatory key-program WISH (Water In Star forming regions with Herschel) concerning high-mass protostars. The program main purpose is to follow the process of star formation during the various stages using the water molecule as a physical diagnostic throughout the evolution. In general, we aim to adress the following questions: How does protostars interact with their environment ? How and where water is formed ? How is it transported from cloud to disk ? When and where water becomes a dominant cooling or heating agent ? We use the HIFI and PACS instruments to obtain maps and spectra of ~20 water lines in ~20 massive protostars spanning a large range in physical parameters, from pre-stellar cores to UCHII regions. I will review the status of the program and focus specifically on the spectroscopic results. I will show how powerful are the HIFI high-resolution spectral observations to resolve different physical source components such as the dense core, the outflows and the extended cold cloud around the high-mass object. We derive water abundances between 10-7 and 10-9 in the outer envelope. The abundance variations derived from our models suggest that different chemical mechanisms are at work on these scales (e.g. evaporation of water-rich icy grain mantles). The detection and derived abundance ratios for rare isotopologues will be discussed. Finally, a comparison in tems

Resolved Companions of Cepheids: Testing the Candidates with X-Ray Observations

Science.gov (United States)

Evans, Nancy Remage; Pillitteri, Ignazio; Wolk, Scott; Karovska, Margarita; Tingle, Evan; Guinan, Edward; Engle, Scott; Bond, Howard E.; Schaefer, Gail H.; Mason, Brian D.

2016-04-01

We have made XMM-Newton observations of 14 Galactic Cepheids that have candidate resolved (≥5″) companion stars based on our earlier HST Wide Field Camera 3 (WFC3) imaging survey. Main-sequence stars that are young enough to be physical companions of Cepheids are expected to be strong X-ray producers in contrast to field stars. XMM-Newton exposures were set to detect essentially all companions hotter than spectral type M0 (corresponding to 0.5 M⊙). The large majority of our candidate companions were not detected in X-rays, and hence are not confirmed as young companions. One resolved candidate (S Nor #4) was unambiguously detected, but the Cepheid is a member of a populous cluster. For this reason, it is likely that S Nor #4 is a cluster member rather than a gravitationally bound companion. Two further Cepheids (S Mus and R Cru) have X-ray emission that might be produced by either the Cepheid or the candidate resolved companion. A subsequent Chandra observation of S Mus shows that the X-rays are at the location of the Cepheid/spectroscopic binary. R Cru and also V659 Cen (also X-ray bright) have possible companions closer than 5″ (the limit for this study) which are the likely sources of X-rays. One final X-ray detection (V473 Lyr) has no known optical companion, so the prime suspect is the Cepheid itself. It is a unique Cepheid with a variable amplitude. The 14 stars that we observed with XMM constitute 36% of the 39 Cepheids found to have candidate companions in our HST/WFC3 optical survey. No young probable binary companions were found with separations of ≥5″ or 4000 au. Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and the USA (NASA).

Effects of mass loss on the evolution of massive stars. I. Main-sequence evolution

International Nuclear Information System (INIS)

Dearborn, D.S.P.; Blake, J.B.; Hainebach, K.L.; Schramm, D.N.

1978-01-01

The effect of mass loss on the evolution and surface composition of massive stars during main-sequence evolution are examined. While some details of the evolutionary track depend on the formula used for the mass loss, the results appear most sensitive to the total mass removed during the main-sequence lifetime. It was found that low mass-loss rates have very little effect on the evolution of a star; the track is slightly subluminous, but the lifetime is almost unaffected. High rates of mass loss lead to a hot, high-luminosity stellar model with a helium core surrounded by a hydrogen-deficient (Xapprox.0.1) envelope. The main-sequence lifetime is extended by a factor of 2--3. These models may be identified with Wolf-Rayet stars. Between these mass-loss extremes are intermediate models which appear as OBN stars on the main sequence. The mass-loss rates required for significant observable effects range from 8 x 10 -7 to 10 -5 M/sub sun/ yr -1 , depending on the initial stellar mass. It is found that observationally consistent mass-loss rates for stars with M> or =30 M/sub sun/ may be sufficiently high that these stars lose mass on a time scale more rapidly than their main-sequence core evolution time. This result implies that the helium cores resulting from the main-sequence evolution of these massive stars may all be very similar to that of a star of Mapprox.30 M/sub sun/ regardless of the zero-age mass

Diffuse remnants of supernova explosions of moving massive stars

Science.gov (United States)

Gvaramadze, V. V.

The modification of the ambient interstellar medium by the wind of massive stars (the progenitors of most of supernovae) results in that the structure and evolution of diffuse supernova remnants (SNRs) significantly deviate from those derived from standard models of SNRs based of the Sedov-Taylor solution. The stellar proper motion and the regular interstellar magnetic field affect the symmetry of the processed medium and cause the SNR to be non-spherically-symmetric. We show that taking into account these effects allows us to explain the diverse morphologies of the known SNRs (the particular attention is paid to the elongated axisymmetric SNRs and the SNRs consisting of two partially overlapping shells) and to infer the ``true" supernova explosion sites in some peculiar SNRs (therefore to search for new neutron stars associated with them).

High-precision atmospheric parameter and abundance determination of massive stars, and consequences for stellar and Galactic evolution

International Nuclear Information System (INIS)

Nieva, Maria-Fernanda; Przybilla, Norbert; Irrgang, Andreas

2011-01-01

The derivation of high precision/accuracy parameters and chemical abundances of massive stars is of utmost importance to the fields of stellar evolution and Galactic chemical evolution. We concentrate on the study of OB-type stars near the main sequence and their evolved progeny, the BA-type supergiants, covering masses of ∼6 to 25 solar masses and a range in effective temperature from ∼8000 to 35 000 K. The minimization of the main sources of systematic errors in the atmospheric model computation, the observed spectra and the quantitative spectral analysis play a critical role in the final results. Our self-consistent spectrum analysis technique employing a robust non-LTE line formation allows precise atmospheric parameters of massive stars to be derived, achieving 1σ-uncertainties as low as 1% in effective temperature and ∼0.05–0.10 dex in surface gravity. Consequences on the behaviour of the chemical elements carbon, nitrogen and oxygen are discussed here in the context of massive star evolution and Galactic chemical evolution, showing tight relations covered in previous work by too large statistical and systematic uncertainties. The spectral analysis of larger star samples, like from the upcoming Gaia-ESO survey, may benefit from these findings.

Effects of stellar evolution and ionizing radiation on the environments of massive stars

Science.gov (United States)

Mackey, J.; Langer, N.; Mohamed, S.; Gvaramadze, V. V.; Neilson, H. R.; Meyer, D. M.-A.

2014-09-01

We discuss two important effects for the astrospheres of runaway stars: the propagation of ionizing photons far beyond the astropause, and the rapid evolution of massive stars (and their winds) near the end of their lives. Hot stars emit ionizing photons with associated photoheating that has a significant dynamical effect on their surroundings. 3-D simulations show that H ii regions around runaway O stars drive expanding conical shells and leave underdense wakes in the medium they pass through. For late O stars this feedback to the interstellar medium is more important than that from stellar winds. Late in life, O stars evolve to cool red supergiants more rapidly than their environment can react, producing transient circumstellar structures such as double bow shocks. This provides an explanation for the bow shock and linear bar-shaped structure observed around Betelgeuse.

A COMPARISON OF SPECTROSCOPIC VERSUS IMAGING TECHNIQUES FOR DETECTING CLOSE COMPANIONS TO KEPLER OBJECTS OF INTEREST

International Nuclear Information System (INIS)

Teske, Johanna K.; Everett, Mark E.; Hirsch, Lea; Furlan, Elise; Ciardi, David R.; Horch, Elliott P.; Howell, Steve B.; Gonzales, Erica; Crepp, Justin R.

2015-01-01

Kepler planet candidates require both spectroscopic and imaging follow-up observations to rule out false positives and detect blended stars. Traditionally, spectroscopy and high-resolution imaging have probed different host star companion parameter spaces, the former detecting tight binaries and the latter detecting wider bound companions as well as chance background stars. In this paper, we examine a sample of 11 Kepler host stars with companions detected by two techniques—near-infrared adaptive optics and/or optical speckle interferometry imaging, and a new spectroscopic deblending method. We compare the companion effective temperatures (T eff ) and flux ratios (F B /F A , where A is the primary and B is the companion) derived from each technique and find no cases where both companion parameters agree within 1σ errors. In 3/11 cases the companion T eff values agree within 1σ errors, and in 2/11 cases the companion F B /F A values agree within 1σ errors. Examining each Kepler system individually considering multiple avenues (isochrone mapping, contrast curves, probability of being bound), we suggest two cases for which the techniques most likely agree in their companion detections (detect the same companion star). Overall, our results support the advantage that the spectroscopic deblending technique has for finding very close-in companions (θ ≲ 0.″02–0.″05) that are not easily detectable with imaging. However, we also specifically show how high-contrast AO and speckle imaging observations detect companions at larger separations (θ ≥ 0.″02–0.″05) that are missed by the spectroscopic technique, provide additional information for characterizing the companion and its potential contamination (e.g., position angle, separation, magnitude differences), and cover a wider range of primary star effective temperatures. The investigation presented here illustrates the utility of combining the two techniques to reveal higher-order multiples in known

A COMPARISON OF SPECTROSCOPIC VERSUS IMAGING TECHNIQUES FOR DETECTING CLOSE COMPANIONS TO KEPLER OBJECTS OF INTEREST

Energy Technology Data Exchange (ETDEWEB)

Teske, Johanna K. [Carnegie DTM, 5241 Broad Branch Road, NW, Washington, DC 20015 (United States); Everett, Mark E. [National Optical Astronomy Observatory, 950 N. Cherry Ave., Tucson, AZ 85719 (United States); Hirsch, Lea [Astronomy Department, University of California at Berkeley, Berkeley, CA 94720 (United States); Furlan, Elise; Ciardi, David R. [NASA Exoplanet Science Institute, California Institute of Technology, 770 South Wilson Ave., Pasadena, CA 91125 (United States); Horch, Elliott P. [Department of Physics, Southern Connecticut State University, 501 Crescent Street, New Haven, CT 06515 (United States); Howell, Steve B. [NASA Ames Research Center, Moffett Field, CA 94035 (United States); Gonzales, Erica; Crepp, Justin R., E-mail: jteske@carnegiescience.edu [Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States)

2015-11-15

Kepler planet candidates require both spectroscopic and imaging follow-up observations to rule out false positives and detect blended stars. Traditionally, spectroscopy and high-resolution imaging have probed different host star companion parameter spaces, the former detecting tight binaries and the latter detecting wider bound companions as well as chance background stars. In this paper, we examine a sample of 11 Kepler host stars with companions detected by two techniques—near-infrared adaptive optics and/or optical speckle interferometry imaging, and a new spectroscopic deblending method. We compare the companion effective temperatures (T{sub eff}) and flux ratios (F{sub B}/F{sub A}, where A is the primary and B is the companion) derived from each technique and find no cases where both companion parameters agree within 1σ errors. In 3/11 cases the companion T{sub eff} values agree within 1σ errors, and in 2/11 cases the companion F{sub B}/F{sub A} values agree within 1σ errors. Examining each Kepler system individually considering multiple avenues (isochrone mapping, contrast curves, probability of being bound), we suggest two cases for which the techniques most likely agree in their companion detections (detect the same companion star). Overall, our results support the advantage that the spectroscopic deblending technique has for finding very close-in companions (θ ≲ 0.″02–0.″05) that are not easily detectable with imaging. However, we also specifically show how high-contrast AO and speckle imaging observations detect companions at larger separations (θ ≥ 0.″02–0.″05) that are missed by the spectroscopic technique, provide additional information for characterizing the companion and its potential contamination (e.g., position angle, separation, magnitude differences), and cover a wider range of primary star effective temperatures. The investigation presented here illustrates the utility of combining the two techniques to reveal higher

The VLT-FLAMES Tarantula Survey. III. A very massive star in apparent isolation from the massive cluster R136

NARCIS (Netherlands)

Bestenlehner, J.M.; Vink, J.S.; Gräfener, G.; Najarro, F.; Evans, C.J.; Bastian, N.; Bonanos, A.Z.; Bressert, E.; Crowther, P.A.; Doran, E.; Friedrich, K.; Hénault-Brunet, V.; Herrero, A.; de Koter, A.; Langer, N.; Lennon, D.J.; Maíz Apellániz, J.; Sana, H.; Soszynski, I.; Taylor, W.D.

2011-01-01

VFTS 682 is located in an active star-forming region, at a projected distance of 29 pc from the young massive cluster R136 in the Tarantula Nebula of the Large Magellanic Cloud. It was previously reported as a candidate young stellar object, and more recently spectroscopically revealed as a

AN M DWARF COMPANION TO AN F-TYPE STAR IN A YOUNG MAIN-SEQUENCE BINARY

Energy Technology Data Exchange (ETDEWEB)

Eigmüller, Ph.; Csizmadia, Sz.; Erikson, A.; Fridlund, M.; Pasternacki, Th.; Rauer, H. [Institute of Planetary Research, German Aerospace Center Rutherfordstr. 2, D-12489 Berlin (Germany); Eislöffel, J.; Lehmann, H.; Hartmann, M.; Hatzes, A. [Thüringer Landessternwarte Tautenburg Sternwarte 5, D-07778 Tautenburg (Germany); Tkachenko, A. [Instituut voor Sterrenkunde, KU Leuven Celestijnenlaan 200D, 3001 Leuven (Belgium); Voss, H., E-mail: philipp.eigmueller@dlr.de [Universitat de Barcelona, Department of Astronomy and Meteorology Martí i Franquès, 1, E-08028 Barcelona (Spain)

2016-03-15

Only a few well characterized very low-mass M dwarfs are known today. Our understanding of M dwarfs is vital as these are the most common stars in our solar neighborhood. We aim to characterize the properties of a rare F+dM stellar system for a better understanding of the low-mass end of the Hertzsprung–Russel diagram. We used photometric light curves and radial velocity follow-up measurements to study the binary. Spectroscopic analysis was used in combination with isochrone fitting to characterize the primary star. The primary star is an early F-type main-sequence star with a mass of (1.493 ± 0.073) M{sub ⊙} and a radius of (1.474 ± 0.040) R{sub ⊙}. The companion is an M dwarf with a mass of (0.188 ± 0.014) M{sub ⊙} and a radius of (0.234 ± 0.009) R{sub ⊙}. The orbital period is (1.35121 ± 0.00001) days. The secondary star is among the lowest-mass M dwarfs known to date. The binary has not reached a 1:1 spin–orbit synchronization. This indicates a young main-sequence binary with an age below ∼250 Myr. The mass–radius relation of both components are in agreement with this finding.

Models of the circumstellar medium of evolving, massive runaway stars moving through the Galactic plane

Science.gov (United States)

Meyer, D. M.-A.; Mackey, J.; Langer, N.; Gvaramadze, V. V.; Mignone, A.; Izzard, R. G.; Kaper, L.

2014-11-01

At least 5 per cent of the massive stars are moving supersonically through the interstellar medium (ISM) and are expected to produce a stellar wind bow shock. We explore how the mass-loss and space velocity of massive runaway stars affect the morphology of their bow shocks. We run two-dimensional axisymmetric hydrodynamical simulations following the evolution of the circumstellar medium of these stars in the Galactic plane from the main sequence to the red supergiant phase. We find that thermal conduction is an important process governing the shape, size and structure of the bow shocks around hot stars, and that they have an optical luminosity mainly produced by forbidden lines, e.g. [O III]. The Hα emission of the bow shocks around hot stars originates from near their contact discontinuity. The Hα emission of bow shocks around cool stars originates from their forward shock, and is too faint to be observed for the bow shocks that we simulate. The emission of optically thin radiation mainly comes from the shocked ISM material. All bow shock models are brighter in the infrared, i.e. the infrared is the most appropriate waveband to search for bow shocks. Our study suggests that the infrared emission comes from near the contact discontinuity for bow shocks of hot stars and from the inner region of shocked wind for bow shocks around cool stars. We predict that, in the Galactic plane, the brightest, i.e. the most easily detectable bow shocks are produced by high-mass stars moving with small space velocities.

A white dwarf companion to the main-sequence star 4 Omicron(1) Orionis and the binary hypothesis for the origin of peculiar red giants

Science.gov (United States)

Ake, Thomas B.; Johnson, Hollis R.

1988-01-01

Ultraviolet spectra of the peculiar red giants (PRGs) called MS stars are investigated, and the discovery of a white dwarf (WD) companion to the MS star 4 Omicron(1) Orionis is reported. The observations and data analysis are discussed and compared with those for field WDs in order to derive parameters for the WD and the luminosity of the primary. Detection limits for the other MS stars investigated are derived, and the binary hypothesis for PRGs is reviewed.

Probing the ejecta of evolved massive stars in transition A VLT/SINFONI K-band survey

Czech Academy of Sciences Publication Activity Database

Oksala, Mary E.; Kraus, Michaela; Cidale, L.S.; Muratore, M.F.; Borges Fernandes, M.

2013-01-01

Roč. 558, October (2013), A17/1-A17/20 ISSN 0004-6361 R&D Projects: GA ČR(CZ) GAP209/11/1198; GA MŠk 7AMB12AR021 Institutional support: RVO:67985815 Keywords : infrared stars * spectroscopic techniques * massive stars Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.479, year: 2013

A TIDALLY DESTRUCTED MASSIVE PLANET AS THE PROGENITOR OF THE TWO LIGHT PLANETS AROUND THE sdB STAR KIC 05807616

International Nuclear Information System (INIS)

Bear, Ealeal; Soker, Noam

2012-01-01

We propose that the two newly detected Earth-size planets around the hot B subdwarf star KIC 05807616 are remnant of the tidally destructed metallic core of a massive planet. A single massive gas-giant planet was spiralling-in inside the envelope of the red giant branch star progenitor of the extreme horizontal branch (EHB) star KIC 05807616. The released gravitational energy unbound most of the stellar envelope, turning it into an EHB star. The massive planet reached the tidal-destruction radius of ∼1 R ☉ from the core, where the planet's gaseous envelope was tidally removed. In our scenario, the metallic core of the massive planet was tidally destructed into several Earth-like bodies immediately after the gaseous envelope of the planet was removed. Two, and possibly more, Earth-size fragments survived at orbital separations of ∼> 1 R ☉ within the gaseous disk. The bodies interact with the disk and among themselves, and migrated to reach orbits close to a 3:2 resonance. These observed planets can have a planetary magnetic field about 10 times as strong as that of Earth. This strong magnetic field can substantially reduce the evaporation rate from the planets and explain their survivability against the strong UV radiation of the EHB star.

The BDNYC database of low-mass stars, brown dwarfs, and planetary mass companions

Science.gov (United States)

Cruz, Kelle; Rodriguez, David; Filippazzo, Joseph; Gonzales, Eileen; Faherty, Jacqueline K.; Rice, Emily; BDNYC

2018-01-01

We present a web-interface to a database of low-mass stars, brown dwarfs, and planetary mass companions. Users can send SELECT SQL queries to the database, perform searches by coordinates or name, check the database inventory on specified objects, and even plot spectra interactively. The initial version of this database contains information for 198 objects and version 2 will contain over 1000 objects. The database currently includes photometric data from 2MASS, WISE, and Spitzer and version 2 will include a significant portion of the publicly available optical and NIR spectra for brown dwarfs. The database is maintained and curated by the BDNYC research group and we welcome contributions from other researchers via GitHub.

Gravitational waves from the collision of tidally disrupted stars with massive black holes

International Nuclear Information System (INIS)

East, William E.

2014-01-01

We use simulations of hydrodynamics coupled with full general relativity to investigate the gravitational waves produced by a star colliding with a massive black hole when the star's tidal disruption radius lies far outside of the black hole horizon. We consider both main-sequence and white-dwarf compaction stars, and nonspinning black holes, as well as those with near-extremal spin. We study the regime in between where the star can be accurately modeled by a point particle, and where tidal effects completely suppress the gravitational wave signal. We find that nonnegligible gravitational waves can be produced even when the star is strongly affected by tidal forces, as well as when it collides with large angular momentum. We discuss the implications that these results have for the potential observation of gravitational waves from these sources with future detectors.

X-RAY AND RADIO OBSERVATIONS OF THE MASSIVE STAR-FORMING REGION IRAS 20126+4104

Energy Technology Data Exchange (ETDEWEB)

Montes, V. A.; Hofner, P.; Anderson, C.; Rosero, V. [Physics Department, New Mexico Tech, 801 Leroy Place, Socorro, NM 87801 (United States)

2015-08-15

We present results from Chandra ACIS-I and Karl G. Jansky Very Large Array 6 cm continuum observations of the IRAS 20126+4104 massive star-forming region. We detect 150 X-ray sources within the 17′ × 17′ ACIS-I field, and a total of 13 radio sources within the 9.′2 primary beam at 4.9 GHz. Among these observtions are the first 6 cm detections of the central sources reported by Hofner et al., namely, I20N1, I20S, and I20var. A new variable radio source is also reported. Searching the 2MASS archive, we identified 88 near-infrared (NIR) counterparts to the X-ray sources. Only four of the X-ray sources had 6 cm counterparts. Based on an NIR color–color analysis and on the Besançon simulation of Galactic stellar populations, we estimate that approximately 80 X-ray sources are associated with this massive star-forming region. We detect an increasing surface density of X-ray sources toward the massive protostar and infer the presence of a cluster of at least 43 young stellar objects within a distance of 1.2 pc from the massive protostar.

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.

Velocity-mass correlation of the O-type stars: model results

International Nuclear Information System (INIS)

Stone, R.C.

1982-01-01

This paper presents new model results describing the evolution of massive close binaries from their initial ZAMS to post-supernova stages. Unlike the previous conservative study by Stone [Astrophys. J. 232, 520 (1979) (Paper II)], these results allow explicitly for mass loss from the binary system occurring during the core hydrogen- and helium-burning stages of the primary binary star as well as during the Roche lobe overflow. Because of uncertainties in these rates, model results are given for several reasonable choices for these rates. All of the models consistently predict an increasing relation between the peculiar space velocities and masses for runaway OB stars which agrees well with the observed correlations discussed in Stone [Astron. J. 86, 544 (1981) (Paper III)] and also predict a lower limit at Mroughly-equal11M/sub sun/ for the masses of runaway stars, in agreement with the observational limit found by A. Blaauw (Bull. Astron. Inst. Neth. 15, 265, 1961), both of which support the binary-supernova scenario described by van den Heuvel and Heise for the origin of runaway stars. These models also predict that the more massive O stars will produce correspondingly more massive compact remnants, and that most binaries experiencing supernova-induced kick velocities of magnitude V/sub k/> or approx. =300 km s -1 will disrupt following the explosions. The best estimate for this velocity as established from pulsar observations is V/sub k/roughly-equal150 km s -1 , in which case probably only 15% if these binaries will be disrupted by the supernova explosions, and therefore, almost all runaway stars should have either neutron star or black hole companions

Four new planets around giant stars and the mass-metallicity correlation of planet-hosting stars

Science.gov (United States)

Jones, M. I.; Jenkins, J. S.; Brahm, R.; Wittenmyer, R. A.; Olivares E., F.; Melo, C. H. F.; Rojo, P.; Jordán, A.; Drass, H.; Butler, R. P.; Wang, L.

2016-05-01

Context. Exoplanet searches have revealed interesting correlations between the stellar properties and the occurrence rate of planets. In particular, different independent surveys have demonstrated that giant planets are preferentially found around metal-rich stars and that their fraction increases with the stellar mass. Aims: During the past six years we have conducted a radial velocity follow-up program of 166 giant stars to detect substellar companions and to characterize their orbital properties. Using this information, we aim to study the role of the stellar evolution in the orbital parameters of the companions and to unveil possible correlations between the stellar properties and the occurrence rate of giant planets. Methods: We took multi-epoch spectra using FEROS and CHIRON for all of our targets, from which we computed precision radial velocities and derived atmospheric and physical parameters. Additionally, velocities computed from UCLES spectra are presented here. By studying the periodic radial velocity signals, we detected the presence of several substellar companions. Results: We present four new planetary systems around the giant stars HIP 8541, HIP 74890, HIP 84056, and HIP 95124. Additionally, we study the correlation between the occurrence rate of giant planets with the stellar mass and metallicity of our targets. We find that giant planets are more frequent around metal-rich stars, reaching a peak in the detection of f = 16.7+15.5-5.9% around stars with [Fe/H] ~ 0.35 dex. Similarly, we observe a positive correlation of the planet occurrence rate with the stellar mass, between M⋆ ~ 1.0 and 2.1 M⊙, with a maximum of f = 13.0+10.1-4.2% at M⋆ = 2.1 M⊙. Conclusions: We conclude that giant planets are preferentially formed around metal-rich stars. In addition, we conclude that they are more efficiently formed around more massive stars, in the stellar mass range of ~1.0-2.1 M⊙. These observational results confirm previous findings for solar

Examining the Center: Positions, Dominance, and Star Formation Rates of Most Massive Group Galaxies at Intermediate Redshift

Science.gov (United States)

Connelly, Jennifer L.; Parker, Laura C.; McGee, Sean; Mulchaey, John S.; Finoguenov, Alexis; Balogh, Michael; Wilman, David; Group Environment Evolution Collaboration

2015-01-01

The group environment is believed to be the stage for many galaxy transformations, helping evolve blue star-forming galaxies to red passive ones. In local studies of galaxy clusters, the central member is usually a single dominant giant galaxy at the center of the potential with little star formation thought to be the result of galaxy mergers. In nearby groups, a range of morphologies and star formation rates are observed and the formation history is less clear. Further, the position and dominance of the central galaxy cannot be assumed in groups, which are less massive and evolved than clusters. To understand the connections between global group properties and properties of the central group galaxy at intermediate redshift, we examine galaxy groups from the Group Environment and Evolution Collaboration (GEEC) catalog, including both optically- and X-ray-selected groups at redshift z~0.4. The sample is diverse, containing a range in overall mass and evolutionary state. The number of groups is significant, membership is notably complete, and measurements span the IR to the UV allowing the properties of the members to be connected to those of the host groups. Having investigated trends in the global group properties previously, including mass and velocity substructure, we turn our attention now to the galaxy populations, focusing on the central regions of these systems. The most massive and second most massive group galaxies are identified by their stellar mass. The positions of the most massive galaxies (MMGs) are determined with respect to both the luminosity-weighted and X-ray center. Star formation rates are used to explore the fraction of passive/quiescent versus star-forming MMGs and the dominance of the MMGs in our group sample is also tested. Determinations of these characteristics and trends constitute the important first steps toward a detailed understanding of the relationships between the properties of host groups and their most massive galaxies and the

Extended high circular polarization in the Orion massive star forming region: implications for the origin of homochirality in the solar system.

Science.gov (United States)

Fukue, Tsubasa; Tamura, Motohide; Kandori, Ryo; Kusakabe, Nobuhiko; Hough, James H; Bailey, Jeremy; Whittet, Douglas C B; Lucas, Philip W; Nakajima, Yasushi; Hashimoto, Jun

2010-06-01

We present a wide-field (approximately 6' x 6') and deep near-infrared (K(s) band: 2.14 mum) circular polarization image in the Orion nebula, where massive stars and many low-mass stars are forming. Our results reveal that a high circular polarization region is spatially extended (approximately 0.4 pc) around the massive star-forming region, the BN/KL nebula. However, other regions, including the linearly polarized Orion bar, show no significant circular polarization. Most of the low-mass young stars do not show detectable extended structure in either linear or circular polarization, in contrast to the BN/KL nebula. If our solar system formed in a massive star-forming region and was irradiated by net circularly polarized radiation, then enantiomeric excesses could have been induced, through asymmetric photochemistry, in the parent bodies of the meteorites and subsequently delivered to Earth. These could then have played a role in the development of biological homochirality on Earth.

Young Stellar Objects in the Massive Star-forming Regions W51 and W43

Energy Technology Data Exchange (ETDEWEB)

Saral, G.; Audard, M. [Department of Astronomy, University of Geneva, Ch. d’Ecogia 16, 1290 Versoix (Switzerland); Hora, J. L.; Martínez-Galarza, J. R.; Smith, H. A. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Koenig, X. P. [Yale University, Department of Astronomy, 208101, New Haven, CT 06520-8101 (United States); Motte, F. [Institut de Plantologie et d’Astrophysique de Grenoble, Univ. Grenoble Alpes—CNRS-INSU, BP 53, F-38041 Grenoble Cedex 9 (France); Nguyen-Luong, Q. [National Astronomical Observatory of Japan, Chile Observatory, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Saygac, A. T. [Istanbul University, Faculty of Science, Astronomy and Space Sciences Department, Istanbul-Turkey (Turkey)

2017-04-20

We present the results of our investigation of the star-forming complexes W51 and W43, two of the brightest in the first Galactic quadrant. In order to determine the young stellar object (YSO) populations in W51 and W43 we used color–magnitude relations based on Spitzer mid-infrared and 2MASS/UKIDSS near-infrared data. We identified 302 Class I YSOs and 1178 Class II/transition disk candidates in W51, and 917 Class I YSOs and 5187 Class II/transition disk candidates in W43. We also identified tens of groups of YSOs in both regions using the Minimal Spanning Tree (MST) method. We found similar cluster densities in both regions, even though Spitzer was not able to probe the densest part of W43. By using the Class II/I ratios, we traced the relative ages within the regions and, based on the morphology of the clusters, we argue that several sites of star formation are independent of one another in terms of their ages and physical conditions. We used spectral energy distribution-fitting to identify the massive YSO (MYSO) candidates since they play a vital role in the star formation process, and then examined them to see if they are related to any massive star formation tracers such as UCH ii regions, masers, or dense fragments. We identified 17 MYSO candidates in W51, and 14 in W43, respectively, and found that groups of YSOs hosting MYSO candidates are positionally associated with H ii regions in W51, though we do not see any MYSO candidates associated with previously identified massive dense fragments in W43.

Supernovae from massive stars with extended tenuous envelopes

Science.gov (United States)

Dessart, Luc; Yoon, Sung-Chul; Livne, Eli; Waldman, Roni

2018-04-01

Massive stars with a core-halo structure are interesting objects for stellar physics and hydrodynamics. Using simulations for stellar evolution, radiation hydrodynamics, and radiative transfer, we study the explosion of stars with an extended and tenuous envelope (i.e. stars in which 95% of the mass is contained within 10% or less of the surface radius). We consider both H-rich supergiant and He-giant progenitors resulting from close-binary evolution and dying with a final mass of 2.8-5 M⊙. An extended envelope causes the supernova (SN) shock to brake and a reverse shock to form, sweeping core material into a dense shell. The shock-deposited energy, which suffers little degradation from expansion, is trapped in ejecta layers of moderate optical depth, thereby enhancing the SN luminosity at early times. With the delayed 56Ni heating, we find that the resulting optical and near-IR light curves all exhibit a double-peak morphology. We show how an extended progenitor can explain the blue and featureless optical spectra of some Type IIb and Ib SNe. The dense shell formed by the reverse shock leads to line profiles with a smaller and near-constant width. This ejecta property can explain the statistically narrower profiles of Type IIb compared to Type Ib SNe, as well as the peculiar Hα profile seen in SN 1993J. At early times, our He-giant star explosion model shows a high luminosity, a blue colour, and featureless spectra reminiscent of the Type Ib SN 2008D, suggesting a low-mass progenitor.

Nucleosynthesis and remnants in massive stars of solar metallicity

International Nuclear Information System (INIS)

Woosley, S.E.; Heger, A.

2007-01-01

Hans Bethe contributed in many ways to our understanding of the supernovae that happen in massive stars, but, to this day, a first principles model of how the explosion is energized is lacking. Nevertheless, a quantitative theory of nucleosynthesis is possible. We present a survey of the nucleosynthesis that occurs in 32 stars of solar metallicity in the mass range 12-120M sun . The most recent set of solar abundances, opacities, mass loss rates, and current estimates of nuclear reaction rates are employed. Restrictions on the mass cut and explosion energy of the supernovae based upon nucleosynthesis, measured neutron star masses, and light curves are discussed and applied. The nucleosynthetic results, when integrated over a Salpeter initial mass function (IMF), agree quite well with what is seen in the sun. We discuss in some detail the production of the long lived radioactivities, 26 Al and 60 Fe, and why recent model-based estimates of the ratio 60 Fe/ 26 Al are overly large compared with what satellites have observed. A major source of the discrepancy is the uncertain nuclear cross sections for the creation and destruction of these unstable isotopes

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...

Black holes in massive close binaries - observational data and evolutionary status

International Nuclear Information System (INIS)

Tutukov, A.V.; Cherepashchuk, A.M.; Moskovskii Gosudarstvennyi Universitet, Moscow, USSR)

1985-01-01

The available information on the mass of four candidate black holes in X-ray binary systems is summarized; these systems are compared with neutron star binaries with regard to the mass of their components. In mass, the relativistic objects form two distinct groups, neutron stars with masses equal to about 1-2 solar masses and black hole candidates with masses equal to about 10-60 solar masses (there seem to be no intermediate cases), but there is no correlation with the mass of the optical star. Mass exchange between the optical component of a close binary and its neutron star companion would be unlikely to produce a black hole more massive than 5-7 solar masses. Instead, the black holes having masses greater than about 10 solar masses might result from core collapse in stars of initial mass equating 20-100 solar masses through either a rise in the presupernova core mass or weakness of the magnetic field. The (10-30)-fold disparity in the incidence of black holes coupled with OB stars and with radio pulsars could indicate that black holes tend to form in pairs. 36 references

The effect of convection and semi-convection on the C/O yield of massive stars

International Nuclear Information System (INIS)

Dearborn, D.S.

1979-01-01

The C/O ratio produced during core helium burning affects the future evolution and nucleosynthetic yield of massive stars. This ratio is shown to be sensitive to the treatment of convection as well as uncertainties in nuclear rates. By minimizing the effect of semi-convection and reducing the size of the convective core, mass loss in OB stars increases the C/O ratio. (Author)

Are Nuclear Star Clusters the Precursors of Massive Black Holes?

Directory of Open Access Journals (Sweden)

Nadine Neumayer

2012-01-01

Full Text Available We present new upper limits for black hole masses in extremely late type spiral galaxies. We confirm that this class of galaxies has black holes with masses less than 106M⊙, if any. We also derive new upper limits for nuclear star cluster masses in massive galaxies with previously determined black hole masses. We use the newly derived upper limits and a literature compilation to study the low mass end of the global-to-nucleus relations. We find the following. (1 The MBH-σ relation cannot flatten at low masses, but may steepen. (2 The MBH-Mbulge relation may well flatten in contrast. (3 The MBH-Sersic n relation is able to account for the large scatter in black hole masses in low-mass disk galaxies. Outliers in the MBH-Sersic n relation seem to be dwarf elliptical galaxies. When plotting MBH versus MNC we find three different regimes: (a nuclear cluster dominated nuclei, (b a transition region, and (c black hole-dominated nuclei. This is consistent with the picture, in which black holes form inside nuclear clusters with a very low-mass fraction. They subsequently grow much faster than the nuclear cluster, destroying it when the ratio MBH/MNC grows above 100. Nuclear star clusters may thus be the precursors of massive black holes in galaxy nuclei.

AN INTERFEROMETRIC AND SPECTROSCOPIC ANALYSIS OF THE MULTIPLE STAR SYSTEM HD 193322

International Nuclear Information System (INIS)

Ten Brummelaar, Theo A.; Farrington, Christopher D.; Schaefer, Gail H.

2011-01-01

The star HD 193322 is a remarkable multiple system of massive stars that lies at the heart of the cluster Collinder 419. Here we report on new spectroscopic observations and radial velocities of the narrow-lined component Ab1 which we use to determine its orbital motion around a close companion Ab2 (P = 312 days) and around a distant third star Aa (P = 35 years). We have also obtained long baseline interferometry of the target in the K' band with the CHARA Array which we use in two ways. First, we combine published speckle interferometric measurements with CHARA separated fringe packet measurements to improve the visual orbit for the wide Aa,Ab binary. Second, we use measurements of the fringe packet from Aa to calibrate the visibility of the fringes of the Ab1,Ab2 binary, and we analyze these fringe visibilities to determine the visual orbit of the close system. The two most massive stars, Aa and Ab1, have masses of approximately 21 and 23 M sun , respectively, and their spectral line broadening indicates that they represent extremes of fast and slow projected rotational velocity, respectively.

Wide-field Infrared Survey Explorer Observations of the Evolution of Massive Star-forming Regions

OpenAIRE

Koenig, X. P.; Leisawitz, D. T.; Benford, D. J.; Rebull, L. M.; Padgett, D. L.; Assef, R. J.

2012-01-01

We present the results of a mid-infrared survey of 11 outer Galaxy massive star-forming regions and 3 open clusters with data from the Wide-field Infrared Survey Explorer (WISE). Using a newly developed photometric scheme to identify young stellar objects and exclude extragalactic contamination, we have studied the distribution of young stars within each region. These data tend to support the hypothesis that latter generations may be triggered by the interaction of winds and radiation from th...

CROWDING-OUT OF GIANTS BY DWARFS: AN ORIGIN FOR THE LACK OF COMPANION PLANETS IN HOT JUPITER SYSTEMS

International Nuclear Information System (INIS)

Ogihara, Masahiro; Inutsuka, Shu-ichiro; Kobayashi, Hiroshi

2013-01-01

We investigate the formation of close-in terrestrial planets from planetary embryos under the influence of a hot Jupiter (HJ) using gravitational N-body simulations that include gravitational interactions between the gas disk and the terrestrial planet (e.g., type I migration). Our simulations show that several terrestrial planets efficiently form outside the orbit of the HJ, making a chain of planets, and all of them gravitationally interact directly or indirectly with the HJ through resonance, which leads to inward migration of the HJ. We call this mechanism of induced migration of the HJ ''crowding-out''. The HJ is eventually lost through collision with the central star, and only several terrestrial planets remain. We also find that the efficiency of the crowding-out effect depends on the model parameters; for example, the heavier the disk is, the more efficient the crowding-out is. When planet formation occurs in a massive disk, the HJ can be lost to the central star and is never observed. On the other hand, for a less massive disk, the HJ and terrestrial planets can coexist; however, the companion planets may be below the detection limit of current observations. In both cases, systems with a HJ and terrestrial planets have little chance of detection. Therefore, our model naturally explains the lack of companion planets in HJ systems regardless of the disk mass. In effect, our model provides a theoretical prediction for future observations; additional planets can be discovered just outside the HJ, and their masses should generally be small

Collisions Between Single Stars in Dense Clusters: Runaway Formation of a Massive Object

NARCIS (Netherlands)

Freitag, M.; Gürkan, M.A.; Rasio, F.A.

2007-01-01

Using Monte Carlo codes, we follow the collisional evolution of clusters in a variety of scenarios. We consider the conditions under which a cluster of main-sequence stars may undergo rapid core collapse due to mass segregation, thus entering a phase of runaway collisions, forming a very massive

CARINA OB STARS: X-RAY SIGNATURES OF WIND SHOCKS AND MAGNETIC FIELDS

International Nuclear Information System (INIS)

Gagne, Marc; Fehon, Garrett; Savoy, Michael R.; Cohen, David H.; Townsley, Leisa K.; Broos, Patrick S.; Povich, Matthew S.; Corcoran, Michael F.; Walborn, Nolan R.; Remage Evans, Nancy; Moffat, Anthony F. J.; Naze, Yael; Oskinova, Lida M.

2011-01-01

The Chandra Carina Complex contains 200 known O- and B-type stars. The Chandra survey detected 68 of the 70 O stars and 61 of 127 known B0-B3 stars. We have assembled a publicly available optical/X-ray database to identify OB stars that depart from the canonical L X /L bol relation or whose average X-ray temperatures exceed 1 keV. Among the single O stars with high kT we identify two candidate magnetically confined wind shock sources: Tr16-22, O8.5 V, and LS 1865, O8.5 V((f)). The O4 III(fc) star HD 93250 exhibits strong, hard, variable X-rays, suggesting that it may be a massive binary with a period of >30 days. The visual O2 If* binary HD 93129A shows soft 0.6 keV and hard 1.9 keV emission components, suggesting embedded wind shocks close to the O2 If* Aa primary and colliding wind shocks between Aa and Ab. Of the 11 known O-type spectroscopic binaries, the long orbital-period systems HD 93343, HD 93403, and QZ Car have higher shock temperatures than short-period systems such as HD 93205 and FO 15. Although the X-rays from most B stars may be produced in the coronae of unseen, low-mass pre-main-sequence companions, a dozen B stars with high L X cannot be explained by a distribution of unseen companions. One of these, SS73 24 in the Treasure Chest cluster, is a new candidate Herbig Be star.

Extreme isolation of WN3/O3 stars and implications for their evolutionary origin as the elusive stripped binaries

Science.gov (United States)

Smith, Nathan; Götberg, Ylva; de Mink, Selma E.

2018-03-01

Recent surveys of the Magellanic Clouds have revealed a subtype of Wolf-Rayet (WR) star with peculiar properties. WN3/O3 spectra exhibit both WR-like emission and O3 V-like absorption - but at lower luminosity than O3 V or WN stars. We examine the projected spatial distribution of WN3/O3 stars in the Large Magellanic Cloud as compared to O-type stars. Surprisingly, WN3/O3 stars are among the most isolated of all classes of massive stars; they have a distribution similar to red supergiants dominated by initial masses of 10-15 M⊙, and are far more dispersed than classical WR stars or luminous blue variables. Their lack of association with clusters of O-type stars suggests strongly that WN3/O3 stars are not the descendants of single massive stars (30 M⊙ or above). Instead, they are likely products of interacting binaries at lower initial mass (10-18 M⊙). Comparison with binary models suggests a probable origin with primaries in this mass range that were stripped of their H envelopes through non-conservative mass transfer by a low-mass secondary. We show that model spectra and positions on the Hertzsprung-Russell diagram for binary-stripped stars are consistent with WN3/O3 stars. Monitoring radial velocities with high-resolution spectra can test for low-mass companions or runaway velocities. With lower initial mass and environments that avoid very massive stars, the WN3/O3 stars fit expectations for progenitors of Type Ib and possibly Type Ibn supernovae.

A new interpretation of luminous blue stars

International Nuclear Information System (INIS)

Stothers, R.

1976-01-01

A major revision of current theoretical ideas about the brightest blue stars must be made if Carson's new radiative opacities are adopted in stellar models. Unlike earlier opacities, the new opacities exhibit a large ''bump'' due to CNO ionization, which leads to very strong central condensation, convective instability, and pulsational instability in hot, diffuse stellar envelopes (typically those in which L/M>10 3 solar units). Despite a number of theoretical uncertainties, the new picture of the structure of very luminous stars is reasonably successful in accounting for a variety of previously unexplained observations. Thus, the new stellar models for the phase of core hydrogen burning predict large radii and rather cool effective temperatures (which are yet to be observationally confirmed) for O stars, and a spreading out of the main-sequence band in the H-R diagram toward luminous cool supergiants for masses higher than approx.20 M/sub sun/, beginning at M/sub v/=-4.5 and Sp=B1. They also predict slower surface rotations for O stars compared with B stars; and, in binary systems, slower apsidal motions, closer rotational-revolutional synchronism, and smaller orbital eccentricities. In massive X-ray binary systems, circular orbits and supergiant-like visual companions are expected to be quite common. Radial pulsations of the models have been calculated by employing linearized nonadiabatic pulsation theory. Long-period variability is predicted to exist for massive blue supergiants of luminosity class Ia. The new models for helium stars predict large radii and rather cool effective temperatures for Wolf-Rayet stars, as well as multimodal pulsational instability and, possibly, surface turbulence for these stars. Ultrashort-period variability, observed in many classes of hot luminous stars, may be due, in part, to high radial overtone pulsations (or, possibly, to nonradial pulsation or convective modes)

Towards a Unified View of Inhomogeneous Stellar Winds in Isolated Supergiant Stars and Supergiant High Mass X-Ray Binaries

Science.gov (United States)

Martínez-Núñez, Silvia; Kretschmar, Peter; Bozzo, Enrico; Oskinova, Lidia M.; Puls, Joachim; Sidoli, Lara; Sundqvist, Jon Olof; Blay, Pere; Falanga, Maurizio; Fürst, Felix; Gímenez-García, Angel; Kreykenbohm, Ingo; Kühnel, Matthias; Sander, Andreas; Torrejón, José Miguel; Wilms, Jörn

2017-10-01

-ray sources in the sky. A large number of them consist of a neutron star accreting from the wind of a massive companion and producing a powerful X-ray source. The characteristics of the stellar wind together with the complex interactions between the compact object and the donor star determine the observed X-ray output from all these systems. Consequently, the use of SgXBs for studies of massive stars is only possible when the physics of the stellar winds, the compact objects, and accretion mechanisms are combined together and confronted with observations. This detailed review summarises the current knowledge on the theory and observations of winds from massive stars, as well as on observations and accretion processes in wind-fed high mass X-ray binaries. The aim is to combine in the near future all available theoretical diagnostics and observational measurements to achieve a unified picture of massive star winds in isolated objects and in binary systems.

Symbiotic stars

Science.gov (United States)

Kafatos, M.; Michalitsianos, A. G.

1984-01-01

The physical characteristics of symbiotic star systems are discussed, based on a review of recent observational data. A model of a symbiotic star system is presented which illustrates how a cool red-giant star is embedded in a nebula whose atoms are ionized by the energetic radiation from its hot compact companion. UV outbursts from symbiotic systems are explained by two principal models: an accretion-disk-outburst model which describes how material expelled from the tenuous envelope of the red giant forms an inwardly-spiralling disk around the hot companion, and a thermonuclear-outburst model in which the companion is specifically a white dwarf which superheats the material expelled from the red giant to the point where thermonuclear reactions occur and radiation is emitted. It is suspected that the evolutionary course of binary systems is predetermined by the initial mass and angular momentum of the gas cloud within which binary stars are born. Since red giants and Mira variables are thought to be stars with a mass of one or two solar mass, it is believed that the original cloud from which a symbiotic system is formed can consist of no more than a few solar masses of gas.

ENHANCED STAR FORMATION OF LESS MASSIVE GALAXIES IN A PROTOCLUSTER AT z = 2.5

Energy Technology Data Exchange (ETDEWEB)

Hayashi, Masao; Kodama, Tadayuki [Optical and Infrared Astronomy Division, National Astronomical Observatory, Mitaka, Tokyo 181-8588 (Japan); Tanaka, Ichi; Koyama, Yusei [Subaru Telescope, National Astronomical Observatory of Japan, 650 North A’ohoku Place, Hilo, HI 96720 (United States); Shimakawa, Rhythm; Suzuki, Tomoko L.; Yamamoto, Moegi [Department of Astronomical Science, SOKENDAI (The Graduate University for Advanced Studies), Mitaka, Tokyo 181-8588 (Japan); Tadaki, Ken-ichi, E-mail: masao.hayashi@nao.ac.jp [Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse, D-85748 Garching (Germany)

2016-08-01

We investigate a correlation between star formation rate (SFR) and stellar mass for H α emission-line galaxies (HAEs) in one of the richest protoclusters ever known at z∼2.5, the USS 1558-003 protocluster. This study is based on a 9.7 hr narrowband imaging data with MOIRCS on the Subaru telescope. We are able to construct a sample in combination with additional H -band data taken with WFC3 on the Hubble Space Telescope , of 100 HAEs reaching the dust-corrected SFRs down to 3 M {sub ⊙} yr{sup −1} and the stellar masses down to 10{sup 8.0} M {sub ⊙}. We find that while the star-forming galaxies with ≳10{sup 9.3} M {sub ⊙} are located on the universal SFR-mass main sequence (MS) irrespective of the environment, less massive star-forming galaxies with ≲10{sup 9.3} M {sub ⊙} show a significant upward scatter from the MS in this protocluster. This suggests that some less massive galaxies are in a starburst phase, although we do not know yet if this is due to environmental effects.

Evolution of massive stars with mass loss: surface abundances

International Nuclear Information System (INIS)

Greggio, L.

1984-01-01

The location of theoretical stellar models in the upper part of the Hertzsprung-Russell diagram depends on a variety of poorly understood physical processes which may occur during the evolution of massive stars. The comparison between theoretical predictions and observations of the surface chemical composition of these objects can help in understanding their evolution and to set more stringent limits to the mentioned parameters. To this end, evolutionary sequences corresponding to 20, 40 and 60 solar masses have been computed up to core He exhaustion, following in detail the abundance variations of CNO, Ne and Mg isotopes. (Auth.)

FROM THE CONVERGENCE OF FILAMENTS TO DISK-OUTFLOW ACCRETION: MASSIVE STAR FORMATION IN W33A

International Nuclear Information System (INIS)

Galvan-Madrid, Roberto; Zhang Qizhou; Keto, Eric; Ho, Paul T. P.; Pineda, Jaime E.; Zapata, Luis A.; RodrIguez, Luis F.; Vazquez-Semadeni, Enrique

2010-01-01

Interferometric observations of the W33A massive star formation region, performed with the Submillimeter Array and the Very Large Array at resolutions from 5'' (0.1 pc) to 0.''5 (0.01 pc), are presented. Our three main findings are: (1) parsec-scale, filamentary structures of cold molecular gas are detected. Two filaments at different velocities intersect in the zone where the star formation is occurring. This is consistent with triggering of the star formation activity by the convergence of such filaments, as predicted by numerical simulations of star formation initiated by converging flows. (2) The two dusty cores (MM1 and MM2) at the intersection of the filaments are found to be at different evolutionary stages, and each of them is resolved into multiple condensations. MM1 and MM2 have markedly different temperatures, continuum spectral indices, molecular-line spectra, and masses of both stars and gas. (3) The dynamics of the 'hot-core' MM1 indicates the presence of a rotating disk in its center (MM1-Main) around a faint free-free source. The stellar mass is estimated to be ∼10 M sun . A massive molecular outflow is observed along the rotation axis of the disk.

Exploring the brown dwarf desert: new substellar companions from the SDSS-III MARVELS survey

Science.gov (United States)

Grieves, Nolan; Ge, Jian; Thomas, Neil; Ma, Bo; Sithajan, Sirinrat; Ghezzi, Luan; Kimock, Ben; Willis, Kevin; De Lee, Nathan; Lee, Brian; Fleming, Scott W.; Agol, Eric; Troup, Nicholas; Paegert, Martin; Schneider, Donald P.; Stassun, Keivan; Varosi, Frank; Zhao, Bo; Jian, Liu; Li, Rui; Porto de Mello, Gustavo F.; Bizyaev, Dmitry; Pan, Kaike; Dutra-Ferreira, Letícia; Lorenzo-Oliveira, Diego; Santiago, Basílio X.; da Costa, Luiz N.; Maia, Marcio A. G.; Ogando, Ricardo L. C.; del Peloso, E. F.

2017-06-01

Planet searches using the radial velocity technique show a paucity of companions to solar-type stars within ˜5 au in the mass range of ˜10-80 MJup. This deficit, known as the brown dwarf desert, currently has no conclusive explanation. New substellar companions in this region help assess the reality of the desert and provide insight to the formation and evolution of these objects. Here, we present 10 new brown dwarf and 2 low-mass stellar companion candidates around solar-type stars from the Multi-object APO Radial Velocity Exoplanet Large-Area Survey (MARVELS) of the Sloan Digital Sky Survey III. These companions were selected from processed MARVELS data using the latest University of Florida Two Dimensional pipeline, which shows significant improvement and reduction of systematic errors over previous pipelines. The 10 brown dwarf companions range in mass from ˜13 to 76 MJup and have orbital radii of less than 1 au. The two stellar companions have minimum masses of ˜98 and 100 MJup. The host stars of the MARVELS brown dwarf sample have a mean metallicity of [Fe/H] = 0.03 ± 0.08 dex. Given our stellar sample we estimate the brown dwarf occurrence rate around solar-type stars with periods less than ˜300 d to be ˜0.56 per cent.

Effect of mass loss on the chemical yields from massive stars

Energy Technology Data Exchange (ETDEWEB)

Chiosi, C; Caimmi, R [Padua Univ. (Italy). Istituto di Astronomia

1979-01-01

Recent results on the calculation of the chemical yields from massive stars, are rediscussed by taking into account the occurrence of mass loss by stellar wind during the core H- and He-burning phases. The new yields are found to be compatible with the observed distribution of chemical abundances in the solar system, except for He. The net enrichment of several elements over the galaxy's lifetime is found to be consistent with the current estimate of the star formation rate, if we adopt a two phase process of galaxy formation (halodisk). The relative He to heavy element enrichment rate ..delta..Y/..delta..Z turns out to agree with the observational value when mass loss by stellar wind is taken into account.

Big Fish in Small Ponds: massive stars in the low-mass clusters of M83

Energy Technology Data Exchange (ETDEWEB)

Andrews, J. E.; Calzetti, D.; McElwee, Sean [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Chandar, R. [Department of Physics and Astronomy, University of Toledo, Toledo, OH 43606 (United States); Elmegreen, B. G. [IBM T. J. Watson Research Center, Yorktown Heights, NY 10598 (United States); Kennicutt, R. C. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Kim, Hwihyun [School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287-1404 (United States); Krumholz, Mark R. [Department of Astronomy and Astrophysics, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States); Lee, J. C.; Whitmore, B. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); O' Connell, R. W., E-mail: jandrews@astro.umass.edu, E-mail: callzetti@astro.umass.edu [Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904-4325 (United States)

2014-09-20

We have used multi-wavelength Hubble Space Telescope WFC3 data of the starbursting spiral galaxy M83 in order to measure variations in the upper end of the stellar initial mass function (uIMF) using the production rate of ionizing photons in unresolved clusters with ages ≤ 8 Myr. As in earlier papers on M51 and NGC 4214, the uIMF in M83 is consistent with a universal IMF, and stochastic sampling of the stellar populations in the ∼<10{sup 3} M {sub ☉} clusters are responsible for any deviations in this universality. The ensemble cluster population, as well as individual clusters, also imply that the most massive star in a cluster does not depend on the cluster mass. In fact, we have found that these small clusters seem to have an over-abundance of ionizing photons when compared to an expected universal or truncated IMF. This also suggests that the presence of massive stars in these clusters does not affect the star formation in a destructive way.

Inferring the star-formation histories of the most massive and passive early-type galaxies at z < 0.3

Science.gov (United States)

Citro, Annalisa; Pozzetti, Lucia; Moresco, Michele; Cimatti, Andrea

2016-07-01

Context. In the Λ cold dark matter (ΛCDM) cosmological framework, massive galaxies are the end-points of the hierarchical evolution and are therefore key probes for understanding how the baryonic matter evolves within the dark matter halos. Aims: The aim of this work is to use the archaeological approach in order to infer the stellar population properties and star formation histories of the most massive (M > 1010.75 M⊙) and passive early-type galaxies (ETGs) at 0 tests have been performed to assess the reliability of STARLIGHT to retrieve the evolutionary properties of the ETG stellar populations such as the age, metallicity and star formation history. The results indicate that these properties can be derived with accuracy better than 10% at S/N ≳ 10-20, and also that the procedure of stacking galaxy spectra does not introduce significant biases into their retrieval. Results: Based on our spectral analysis, we found that the ETGs of our sample are very old systems - the most massive ones are almost as old as the Universe. The stellar metallicities are slightly supersolar, with a mean of Z ~ 0.027 ± 0.002 and Z ~ 0.029 ± 0.0015 (depending on the spectral synthesis models used for the fit) and do not depend on redshift. Dust extinction is very low, with a mean of AV ~ 0.08 ± 0.030 mag and AV ~ 0.16 ± 0.048 mag. The ETGs show an anti-hierarchical evolution (downsizing) where more massive galaxies are older. The SFHs can be approximated with a parametric function of the form SFR(t) ∝ τ- (c + 1)tc exp(-t/τ), with typical short e-folding times of τ ~ 0.6-0.8 Gyr (with a dispersion of ±0.1 Gyr) and c ~ 0.1 (with a dispersion of ±0.05). Based on the reconstructed SFHs, most of the stellar mass (≳75%) was assembled by z ~ 5 and ≲4% of it can be ascribed to stellar populations younger than ~1 Gyr. The inferred SFHs are also used to place constraints on the properties and evolution of the ETG progenitors. In particular, the ETGs of our samples should have

Models for the formation of binary and millisecond radio pulsars

International Nuclear Information System (INIS)

van den Heuvel, E.P.J.

1984-01-01

The peculiar combination of a relatively short pulse period and a relatively weak surface dipole magnetic field strength of binary radio pulsars finds a consistent explanation in terms of: (i) decay of the surface dipole component of neutron star magnetic fields on a timescale of (2-5).10 6 yrs, in combination with: (ii) spin up of the rotation of the neutron star during a subsequent mass-transfer phase. The two observed classes of binary radio pulsars (very close and very wide systems, respectively) are expected to have been formed by the later evolution of binaries consisting of a neutron star and a normal companion star, in which the companion was (considerably) more massive than the neutron star, or less massive than the neutron star, respectively. In the first case the companion of the neutron star in the final system will be a fairly massive white dwarf, in a circular orbit, or a neutron star in an eccentric orbit. In the second case the final companion to the neutron star will be a low-mass (approx. 0.3 Msub solar) helium white dwarf in a wide and nearly circular orbit. In systems of the second type the neutron star was most probably formed by the accretion-induced collapse of a white dwarf. This explains why PSR 1953+29 has a millisecond rotation period and why PSR 0820+02 has not. Binary coalescence models for the formation of the 1.5 millisecond pulsar appear to be viable. The companion to the neutron star may have been a low-mass red dwarf, a neutron star, or a massive (> 0.7 Msub solar) white dwarf. In the red-dwarf case the progenitor system probably was a CV binary in which the white dwarf collapsed by accretion. 66 references, 6 figures, 1 table

An astrometric search for a stellar companion to the sun

International Nuclear Information System (INIS)

Perlmutter, S.

1986-01-01

A companion star within 0.8 pc of the Sun has been postulated to explain a possible 26 Myr periodicity in mass extinctions of species on the Earth. Such a star would already be catalogued in the Yale Bright Star catalogue unless it is fainter than m/sub nu/ = 6.5; this limits the possible stellar types for an unseen companion to red dwarfs, brown dwarfs, or compact objects. Red dwarfs account for about 75% of these possible stars. We describe here the design and development of an astrometric search for a nearby red dwarf companion with a six-month peak-to-peak parallax of ≥2.5 arcseconds. We are measuring the parallax of 2770 candidate faint red stars selected from the Dearborn Observatory catalogue. An automated 30-inch telescope and CCD camera system collect digitized images of the candidate stars, along with a 13' x 16' surrounding field of background stars. Second-epoch images, taken a few months later, are registered to the first epoch images using the background stars as fiducials. An apparent motion, m/sub a/, of the candidate stars is found to a precision of σ/sub m//sub a/ ≅ 0.08 pixel ≅ 0.2 arcseconds for fields with N/sub fiducial/ ≥ 10 fiducial stars visible above the background noise. This precision is sufficient to detect the parallactic motion of a star at 0.8 pc with a two month interval between the observation epochs. Images with fewer fiducial stars above background noise are observed with a longer interval between epochs. If a star is found with high parallactic motion, we will confirm its distance with further parallax measurements, photometry, and spectral studies, and will measure radial velocity and proper motion to establish its orbit. We have demonstrated the search procedure with observations of 41 stars, and have shown that none of these is a nearby star. 37 refs., 16 figs., 3 tabs

Close companions to two high-redshift quasars

Energy Technology Data Exchange (ETDEWEB)

McGreer, Ian D.; Fan, Xiaohui; Bian, Fuyan [Steward Observatory, The University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721-0065 (United States); Strauss, Michael A. [Princeton University Observatory, Peyton Hall, Princeton, NJ 08544 (United States); Haiman, Zoltàn [Department of Astronomy, Columbia University, 550 West 120th Street, New York, NY 10027 (United States); Richards, Gordon T. [Department of Physics, Drexel University, 3141 Chestnut Street, Philadelphia, PA 19104 (United States); Jiang, Linhua [School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287 (United States); Schneider, Donald P., E-mail: imcgreer@as.arizona.edu [Department of Astronomy and Astrophysics and the Institute for Gravitation and the Cosmos, The Pennsylvania State University, University Park, PA 16802 (United States)

2014-10-01

We report the serendipitous discoveries of companion galaxies to two high-redshift quasars. SDSS J025617.7+001904 is a z = 4.79 quasar included in our recent survey of faint quasars in the SDSS Stripe 82 region. The initial MMT slit spectroscopy shows excess Lyα emission extending well beyond the quasar's light profile. Further imaging and spectroscopy with LBT/MODS1 confirms the presence of a bright galaxy (i {sub AB} = 23.6) located 2'' (12 kpc projected) from the quasar with strong Lyα emission (EW{sub 0} ≈ 100 Å) at the redshift of the quasar, as well as faint continuum. The second quasar, CFHQS J005006.6+344522 (z = 6.25), is included in our recent HST SNAP survey of z ∼ 6 quasars searching for evidence of gravitational lensing. Deep imaging with ACS and WFC3 confirms an optical dropout ∼4.5 mag fainter than the quasar (Y {sub AB} = 25) at a separation of 0.''9. The red i {sub 775} – Y {sub 105} color of the galaxy and its proximity to the quasar (5 kpc projected if at the quasar redshift) strongly favor an association with the quasar. Although it is much fainter than the quasar, it is remarkably bright when compared to field galaxies at this redshift, while showing no evidence for lensing. Both systems may represent late-stage mergers of two massive galaxies, with the observed light for one dominated by powerful ongoing star formation and for the other by rapid black hole growth. Observations of close companions are rare; if major mergers are primarily responsible for high-redshift quasar fueling then the phase when progenitor galaxies can be observed as bright companions is relatively short.

Hubble Space Telescope Snapshot Survey for Resolved Companions of Galactic Cepheids

Science.gov (United States)

Evans, Nancy Remage; Bond, Howard E.; Schaefer, Gail H.; Mason, Brian D.; Tingle, Evan; Karovska, Margarita; Pillitteri, Ignazio

2016-05-01

We have conducted an imaging survey with the Hubble Space Telescope Wide Field Camera 3 (WFC3) of 70 Galactic Cepheids, typically within 1 kpc, with the aim of finding resolved physical companions. The WFC3 field typically covers the 0.1 pc area where companions are expected. In this paper, we identify 39 Cepheids having candidate companions, based on their positions in color-magnitude diagrams, and having separations ⩾ 5'' from the Cepheids. We use follow-up observations of 14 of these candidates with XMM-Newton, and of one of them with ROSAT, to separate X-ray-active young stars (probable physical companions) from field stars (chance alignments). Our preliminary estimate, based on the optical and X-ray observations, is that only 3% of the Cepheids in the sample have wide companions. Our survey easily detects resolved main-sequence companions as faint as spectral type K. Thus the fact that the two most probable companions (those of FF Aql and RV Sco) are earlier than type K is not simply a function of the detection limit. We find no physical companions having separations larger than 4000 au in the X-ray survey. Two Cepheids are exceptions in that they do have young companions at significantly larger separations (δ Cep and S Nor), but both belong to a cluster or a loose association, so our working model is that they are not gravitationally bound binary members, but rather cluster/association members. All of these properties provide constraints on both star formation and subsequent dynamical evolution. The low frequency of true physical companions at separations > 5'' is confirmed by examination of the subset of the nearest Cepheids and also the density of the fields. Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

Tracking Advanced Planetary Systems (TAPAS) with HARPS-N. V. A Massive Jupiter orbiting the very-low-metallicity giant star BD+03 2562 and a possible planet around HD 103485

Science.gov (United States)

Villaver, E.; Niedzielski, A.; Wolszczan, A.; Nowak, G.; Kowalik, K.; Adamów, M.; Maciejewski, G.; Deka-Szymankiewicz, B.; Maldonado, J.

2017-10-01

planetary companions, they represent systems orbiting very evolved stars with very low metallicities, a challenge to the conditions required for the formation of massive giant gas planets. Based on observations obtained with the Hobby-Eberly Telescope, which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen.Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Fundación Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.

Radiative Feedback from Massive Stars as Traced by Multiband Imaging and Spectroscopic Mosaics

Science.gov (United States)

Tielens, Alexander; "PDRs4ever" team

2018-06-01

Massive stars disrupt their natal molecular cloud material by dissociating molecules, ionizing atoms and molecules, and heating the gas and dust. These processes drive the evolution of interstellar matter in our Galaxy and throughout the Universe from the era of vigorous star formation at redshifts of 1-3, to the present day. Much of this interaction occurs in Photo-Dissociation Regions (PDRs) where far-ultraviolet photons of these stars create a largely neutral, but warm region of gas and dust. PDR emission dominates the IR spectra of star-forming galaxies and also provides a unique tool to study in detail the physical and chemical processes that are relevant for inter- and circumstellar media including diffuse clouds, molecular cloud and protoplanetary disk surfaces, globules, planetary nebulae, and starburst galaxies.We propose to provide template datasets designed to identify key PDR characteristics in the full 1-28 μm JWST spectra in order to guide the preparation of Cycle 2 proposals on star-forming regions in our Galaxy and beyond. We plan to obtain the first spatially resolved, high spectral resolution IR observations of a PDR using NIRCam, NIRSpec and MIRI. We will observe a nearby PDR with well-defined UV illumination in a typical massive star-forming region. JWST observations will, for the first time, spatially resolve and perform a tomography of the PDR, revealing the individual IR spectral signatures from the key zones and sub-regions within the ionized gas, the PDR and the molecular cloud. These data will test widely used theoretical models and extend them into the JWST era. We will assist the community interested in JWST observations of PDRs through several science-enabling products (maps of spectral features, template spectra, calibration of narrow/broad band filters in gas lines and PAH bands, data-interpretation tools e.g. to infer gas physical conditions or PAH and dust characteristics). This project is supported by a large international team of

Proposal for lower frequency companions for the advanced LIGO Gravitational Wave Interferometric Detectors

International Nuclear Information System (INIS)

Conforto, Gianni; De Salvo, Riccardo

2004-01-01

Recent X-ray observations of many galaxies, combined with optical observations of Galactic globular clusters, provide evidence for a population of Black Holes (BH) with masses of hundreds to thousands of solar masses. These candidate intermediate-mass BHs are often found in high density stellar clusters, where dynamical braking is rapid and hence massive stars are expected to sink to the center of the clusters within a few million years. In this same timescale, heavy star binary systems are expected to undergo numerous three-body interactions, tightening them and causing massive BHs to undergo multiple coalescences. At the BH masses implied by observations, these coalescences will take place below 100 Hz. There are advances in technology that make instruments to observe these events feasible. For example, new measurements of fused silica quality factors, as well as new wide beam technologies, can drive the thermal noise of large mirrors sufficiently low to allow monitoring of these low frequency BH-BH inspirals. It is possible to suspend an additional LF interferometer in the advanced LIGO beam pipes and within the existing LIGO facilities. This additional interferometer could be operated simultaneously with the advanced LIGO ones, thus providing both matching companions for the LF Virgo GW interferometer, and suitable triggers for higher frequency merging and ring-down signals to be measured in advanced LIGO

How Very Massive Metal-Free Stars Start Cosmological Reionization

Science.gov (United States)

Wise, John H.; Abel, Tom

2008-01-01

The initial conditions and relevant physics for the formation of the earliest galaxies are well specified in the concordance cosmology. Using ab initio cosmological Eulerian adaptive mesh refinement radiation hydrodynamical calculations, we discuss how very massive stars start the process of cosmological reionization. The models include nonequilibrium primordial gas chemistry and cooling processes and accurate radiation transport in the case B approximation using adaptively ray-traced photon packages, retaining the time derivative in the transport equation. Supernova feedback is modeled by thermal explosions triggered at parsec scales. All calculations resolve the local Jeans length by at least 16 grid cells at all times and as such cover a spatial dynamic range of approx.10(exp 6). These first sources of reionization are highly intermittent and anisotropic and first photoionize the small-scale voids surrounding the halos they form in, rather than the dense filaments they are embedded in. As the merging objects form larger, dwarf-sized galaxies, the escape fraction of UV radiation decreases and the H II regions only break out on some sides of the galaxies, making them even more anisotropic. In three cases, SN blast waves induce star formation in overdense regions that were formed earlier from ionization front instabilities. These stars form tens of parsecs away from the center of their parent DM halo. Approximately five ionizing photons are needed per sustained ionization when star formation in 10(exp 6) stellar Mass halos is dominant in the calculation. As the halos become larger than approx.10(exp 7) Stellar Mass, the ionizing photon escape fraction decreases, which in turn increases the number of photons per ionization to 15-50, in calculations with stellar feedback only. Radiative feedback decreases clumping factors by 25% when compared to simulations without star formation and increases the average temperature of ionized gas to values between 3000 and 10,000 K.

General Relativity and Compact Stars

International Nuclear Information System (INIS)

Glendenning, Norman K.

2005-01-01

Compact stars--broadly grouped as neutron stars and white dwarfs--are the ashes of luminous stars. One or the other is the fate that awaits the cores of most stars after a lifetime of tens to thousands of millions of years. Whichever of these objects is formed at the end of the life of a particular luminous star, the compact object will live in many respects unchanged from the state in which it was formed. Neutron stars themselves can take several forms--hyperon, hybrid, or strange quark star. Likewise white dwarfs take different forms though only in the dominant nuclear species. A black hole is probably the fate of the most massive stars, an inaccessible region of spacetime into which the entire star, ashes and all, falls at the end of the luminous phase. Neutron stars are the smallest, densest stars known. Like all stars, neutron stars rotate--some as many as a few hundred times a second. A star rotating at such a rate will experience an enormous centrifugal force that must be balanced by gravity or else it will be ripped apart. The balance of the two forces informs us of the lower limit on the stellar density. Neutron stars are 10 14 times denser than Earth. Some neutron stars are in binary orbit with a companion. Application of orbital mechanics allows an assessment of masses in some cases. The mass of a neutron star is typically 1.5 solar masses. They can therefore infer their radii: about ten kilometers. Into such a small object, the entire mass of our sun and more, is compressed

Proca stars: Gravitating Bose–Einstein condensates of massive spin 1 particles

Directory of Open Access Journals (Sweden)

Richard Brito

2016-01-01

Full Text Available We establish that massive complex Abelian vector fields (mass μ can form gravitating solitons, when minimally coupled to Einstein's gravity. Such Proca stars (PSs have a stationary, everywhere regular and asymptotically flat geometry. The Proca field, however, possesses a harmonic time dependence (frequency w, realizing Wheeler's concept of geons for an Abelian spin 1 field. We obtain PSs with both a spherically symmetric (static and an axially symmetric (stationary line element. The latter form a countable number of families labelled by an integer m∈Z+. PSs, like (scalar boson stars, carry a conserved Noether charge, and are akin to the latter in many ways. In particular, both types of stars exist for a limited range of frequencies and there is a maximal ADM mass, Mmax, attained for an intermediate frequency. For spherically symmetric PSs (rotating PSs with m=1,2,3, Mmax≃1.058MPl2/μ (Mmax≃1.568,2.337,3.247MPl2/μ, slightly larger values than those for (mini-boson stars. We establish perturbative stability for a subset of solutions in the spherical case and anticipate a similar conclusion for fundamental modes in the rotating case. The discovery of PSs opens many avenues of research, reconsidering five decades of work on (scalar boson stars, in particular as possible dark matter candidates.

Massive stars, x-ray ridge, and galactic 26Al gamma-ray line emission

International Nuclear Information System (INIS)

Montmerle, T.

1986-07-01

Massive stars interact with their parent molecular cloud by means of their ionizing flux and strong winds, thereby creating giant, hollow HII regions. To account for the observed structure of these HII regions, it appears necessary that all the wind energy be dissipated. Dorland and Montmerle have recently proposed a new dissipation mechanism, in the process, diffuse hard X-rays are emitted. If the observed galactic X-ray ''ridge'' results from this process on a galactic scale, it can be accounted for by the interaction of ∼3000 Wolf-Rayet stars (mostly within a ∼6.5 kpc ring) with their surrounding interstellar gas. This result is essentially consistent with the suggestion by Prantzos and Casse that the galactic 26 Al γ-ray line emission originates in Wolf-Rayet stars

Enhanced winds and tidal streams in massive X-ray binaries

International Nuclear Information System (INIS)

Blondin, J.M.; Stevens, I.R.; Kallman, T.R.

1991-01-01

The tidal effects created by the presence of a compact companion are expected to induce a stream of enhanced wind from the early-type primary star in massive X-ray binary systems. In this paper, two-dimensional gasdynamical simulations of such streams are presented. It is found that the wind enhancement is a sensitive function of the binary separation, and develops into a tidal stream as the primary approaches its critical surface. For typical system parameters, the Coriolis force deflects the stream sufficiently that it does not impact directly on the compact companion but passes behind it. The density in the stream can reach values of 20-30 times the ambient wind density, leading to strong attenuation of the X-ray flux that passes through the tidal stream, providing a possible explanation of the enhanced absorption events seen at later phases in the X-ray observations of massive X-ray binary systems such as Vela X-1. In contrast to the time-variable accretion wake, the tidal stream is relatively stationary, producing absorption features that should remain fixed from orbit to orbit. For systems with a strong tidal stream, the large asymmetry in the accreting wind results in the accretion of angular momentum of constant sign, as opposed to systems without streams, where the sign of the accreted angular momentum can change. 39 refs

On the Ultimate Fate of Massive Neutron Stars in an Ever Expanding Universe

Science.gov (United States)

Hujeirat, Ahmad A.

2018-01-01

General theory of relativity predicts the central densities of massive neutron stars (-MANs) to be much larger than the nuclear density. In the absence of energy production, the lifetimes of MANs should be shorter that their low-mass counterparts. Yet neither black holes nor neutron stars, whose masses are between two and five solar masses have ever been observed. Also, it is not clear what happened to the old MANs that were created through the collapse of first generation of stars shortly after the Big Bang. In this article, it is argued that MANs must end as completely invisible objects, whose cores are made of incompressible quark-gluon-superfluids and that their effective masses must have doubled through the injection of dark energy by a universal scalar field at the background of supranuclear density. It turns out that recent glitch observations of pulsars and young neutron star systems and data from particle collisions at the LHC and RHIC are in line with the presen! t scenario.

Heaviest Stellar Black Hole Discovered in Nearby Galaxy

Science.gov (United States)

2007-10-01

Astronomers have located an exceptionally massive black hole in orbit around a huge companion star. This result has intriguing implications for the evolution and ultimate fate of massive stars. The black hole is part of a binary system in M33, a nearby galaxy about 3 million light years from Earth. By combining data from NASA's Chandra X-ray Observatory and the Gemini telescope on Mauna Kea, Hawaii, the mass of the black hole, known as M33 X-7, was determined to be 15.7 times that of the Sun. This makes M33 X-7 the most massive stellar black hole known. A stellar black hole is formed from the collapse of the core of a massive star at the end of its life. Chandra X-ray Image of M33 X-7 Chandra X-ray Image of M33 X-7 "This discovery raises all sorts of questions about how such a big black hole could have been formed," said Jerome Orosz of San Diego State University, lead author of the paper appearing in the October 18th issue of the journal Nature. M33 X-7 orbits a companion star that eclipses the black hole every three and a half days. The companion star also has an unusually large mass, 70 times that of the Sun. This makes it the most massive companion star in a binary system containing a black hole. Hubble Optical Image of M33 X-7 Hubble Optical Image of M33 X-7 "This is a huge star that is partnered with a huge black hole," said coauthor Jeffrey McClintock of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. "Eventually, the companion will also go supernova and then we'll have a pair of black holes." The properties of the M33 X-7 binary system - a massive black hole in a close orbit around a massive companion star - are difficult to explain using conventional models for the evolution of massive stars. The parent star for the black hole must have had a mass greater than the existing companion in order to have formed a black hole before the companion star. Gemini Optical Image of M33 X-7 Gemini Optical Image of M33 X-7 Such a massive star would

THE THREE-DIMENSIONAL EVOLUTION TO CORE COLLAPSE OF A MASSIVE STAR

Energy Technology Data Exchange (ETDEWEB)

Couch, Sean M. [TAPIR, Walter Burke Institute for Theoretical Physics, California Institute of Technology, Pasadena, CA 91125 (United States); Chatzopoulos, Emmanouil [Flash Center for Computational Science, Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL 60637 (United States); Arnett, W. David [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States); Timmes, F. X., E-mail: smc@tapir.caltech.edu [Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, MI 48824 (United States)

2015-07-20

We present the first three-dimensional (3D) simulation of the final minutes of iron core growth in a massive star, up to and including the point of core gravitational instability and collapse. We capture the development of strong convection driven by violent Si burning in the shell surrounding the iron core. This convective burning builds the iron core to its critical mass and collapse ensues, driven by electron capture and photodisintegration. The non-spherical structure and motion generated by 3D convection is substantial at the point of collapse, with convective speeds of several hundreds of km s{sup −1}. We examine the impact of such physically realistic 3D initial conditions on the core-collapse supernova mechanism using 3D simulations including multispecies neutrino leakage and find that the enhanced post-shock turbulence resulting from 3D progenitor structure aids successful explosions. We conclude that non-spherical progenitor structure should not be ignored, and should have a significant and favorable impact on the likelihood for neutrino-driven explosions. In order to make simulating the 3D collapse of an iron core feasible, we were forced to make approximations to the nuclear network making this effort only a first step toward accurate, self-consistent 3D stellar evolution models of the end states of massive stars.

THE THREE-DIMENSIONAL EVOLUTION TO CORE COLLAPSE OF A MASSIVE STAR

International Nuclear Information System (INIS)

Couch, Sean M.; Chatzopoulos, Emmanouil; Arnett, W. David; Timmes, F. X.

2015-01-01

We present the first three-dimensional (3D) simulation of the final minutes of iron core growth in a massive star, up to and including the point of core gravitational instability and collapse. We capture the development of strong convection driven by violent Si burning in the shell surrounding the iron core. This convective burning builds the iron core to its critical mass and collapse ensues, driven by electron capture and photodisintegration. The non-spherical structure and motion generated by 3D convection is substantial at the point of collapse, with convective speeds of several hundreds of km s −1 . We examine the impact of such physically realistic 3D initial conditions on the core-collapse supernova mechanism using 3D simulations including multispecies neutrino leakage and find that the enhanced post-shock turbulence resulting from 3D progenitor structure aids successful explosions. We conclude that non-spherical progenitor structure should not be ignored, and should have a significant and favorable impact on the likelihood for neutrino-driven explosions. In order to make simulating the 3D collapse of an iron core feasible, we were forced to make approximations to the nuclear network making this effort only a first step toward accurate, self-consistent 3D stellar evolution models of the end states of massive stars

RADIAL VELOCITIES OF GALACTIC O-TYPE STARS. II. SINGLE-LINED SPECTROSCOPIC BINARIES

International Nuclear Information System (INIS)

Williams, S. J.; Gies, D. R.; Hillwig, T. C.; McSwain, M. V.; Huang, W.

2013-01-01

We report on new radial velocity measurements of massive stars that are either suspected binaries or lacking prior observations. This is part of a survey to identify and characterize spectroscopic binaries among O-type stars with the goal of comparing the binary fraction of field and runaway stars with those in clusters and associations. We present orbits for HDE 308813, HD 152147, HD 164536, BD–16°4826, and HDE 229232, Galactic O-type stars exhibiting single-lined spectroscopic variation. By fitting model spectra to our observed spectra, we obtain estimates for effective temperature, surface gravity, and rotational velocity. We compute orbital periods and velocity semiamplitudes for each system and note the lack of photometric variation for any system. These binaries probably appear single-lined because the companions are faint and because their orbital Doppler shifts are small compared to the width of the rotationally broadened lines of the primary.

Impact of the uncertainty in α-captures on {sup 22}Ne on the weak s-process in massive stars

Energy Technology Data Exchange (ETDEWEB)

Nishimura, N. [Astrophysics group, EPSAM, Keele University, Keele, ST5 1BH, UK and NuGrid Project (United Kingdom); Hirschi, R. [Astrophysics group, EPSAM, Keele University, Keele, ST5 1BH, UK and Kavli IPMU (WPI), University of Tokyo, Kashiwa, 277-8583 (Japan); Pignatari, M. [NuGrid Project and Department of Physics, University of Basel, Basel, CH-4056 (Switzerland); Herwig, F. [NuGrid Project and Department of Physics and Astronomy, University of Victoria, Victoria, BC V8P5C2 (Canada); Beard, M. [NuGrid Project and Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States); Imbriani, G. [Dipartiment di Scienze Fisiche, Universita di Napoli Federico II, Napoli (Italy); Görres, J.; Boer, R. J. de; Wiescher, M. [Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States)

2014-05-02

Massive stars at solar metallicity contribute to the production of heavy elements with atomic masses between A = 60 and A = 90 via the so-called weak s-process (which takes place during core He and shell C burning phases). Furthermore, recent studies have shown that rotation boosts the s-process production in massive stars at low metallicities, with a production that may reach the barium neutron-magic peak. These results are very sensitive to neutron source and neutron poison reaction rates. For the weak s-process, the main neutron source is the reaction {sup 22}Ne(α,n){sup 25}Mg, which is in competition with {sup 22}Ne(α,γ){sup 26}Mg. The uncertainty of both rates strongly affects the nucleosynthesis predictions from stellar model calculations. In this study, we investigate the impact of the uncertainty in α-captures on {sup 22}Ne on the s-process nucleosynthesis in massive stars both at solar and at very low metallicity. For this purpose, we post-process, with the Nugrid mppnp code, non-rotating and rotating evolutionary models 25M{sub ⊙} stars at two different metallicities: Z = Z{sub ⊙} and Z = 10{sup −5}Z{sub ⊙}, respectively. Our results show that uncertainty of {sup 22}Ne(α,n){sup 25}Mg and {sup 22}Ne(α,γ){sup 26}Mg rates have a significant impact on the final elemental production especially for metal poor rotating models. Beside uncertainties in the neutron source reactions, for fast rotating massive stars at low metallicity we revisit the impact of the neutron poisoning effect by the reaction chain {sup 16}O(n,γ){sup 17}O(α,γ){sup 21}Ne, in competition with the {sup 17}O(α,n){sup 20}Ne, recycling the neutrons captured by {sup 16}O.

SPITZER MICROLENS MEASUREMENT OF A MASSIVE REMNANT IN A WELL-SEPARATED BINARY

Energy Technology Data Exchange (ETDEWEB)

Shvartzvald, Y.; Bryden, G.; Henderson, C. B. [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Udalski, A. [Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa (Poland); Gould, A.; Fausnaugh, M.; Gaudi, B. S.; Pogge, R. W.; Wibking, B.; Zhu, W. [Department of Astronomy, Ohio State University, 140 W. 18th Avenue, Columbus, OH 43210 (United States); Han, C. [Department of Physics, Chungbuk National University, Cheongju 361-763 (Korea, Republic of); Bozza, V.; Novati, S. Calchi [Dipartimento di Fisica “E. R. Caianiello,” Università di Salerno, Via Giovanni Paolo II, I-84084 Fisciano (Italy); Friedmann, M. [School of Physics and Astronomy, Tel-Aviv University, Tel-Aviv 69978 (Israel); Hundertmark, M. [Niels Bohr Institute and Centre for Star and Planet Formation, University of Copenhagen, Øster Voldgade 5, DK-1350 Copenhagen K (Denmark); Beichman, C. [NASA Exoplanet Science Institute, MS 100-22, California Institute of Technology, Pasadena, CA 91125 (United States); Carey, S. [Spitzer, Science Center, MS 220-6, California Institute of Technology, Pasadena, CA (United States); Kerr, T.; Varricatt, W. [UKIRT, 660 N. Aohoku Place, University Park, Hilo, HI 96720 (United States); Yee, J. C. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Collaboration: and; Spitzer team; OGLE group; KMTNet group; Wise group; RoboNet; MiNDSTEp; and others

2015-12-01

We report the detection and mass measurement of a binary lens OGLE-2015-BLG-1285La,b, with the more massive component having M{sub 1} > 1.35 M{sub ⊙} (80% probability). A main-sequence star in this mass range is ruled out by limits on blue light, meaning that a primary in this mass range must be a neutron star (NS) or black hole (BH). The system has a projected separation r{sub ⊥} = 6.1 ± 0.4 AU and lies in the Galactic bulge. These measurements are based on the “microlens parallax” effect, i.e., comparing the microlensing light curve as seen from Spitzer, which lay at 1.25 AU projected from Earth, to the light curves from four ground-based surveys, three in the optical and one in the near-infrared. Future adaptive optics imaging of the companion by 30 m class telescopes will yield a much more accurate measurement of the primary mass. This discovery both opens the path and defines the challenges to detecting and characterizing BHs and NSs in wide binaries, with either dark or luminous companions. In particular, we discuss lessons that can be applied to future Spitzer and Kepler K2 microlensing parallax observations.

The comparison of physical properties derived from gas and dust in a massive star-forming region

Energy Technology Data Exchange (ETDEWEB)

Battersby, Cara; Bally, John; Ginsburg, Adam; Darling, Jeremy [Center for Astrophysics and Space Astronomy, University of Colorado, UCB 389, Boulder, CO 80309 (United States); Dunham, Miranda [Department of Astronomy, Yale University, New Haven, CT 06520 (United States); Longmore, Steve [Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead CH41 1LD (United Kingdom)

2014-05-10

We explore the relationship between gas and dust in a massive star-forming region by comparing the physical properties derived from each. We compare the temperatures and column densities in a massive star-forming Infrared Dark Cloud (G32.02+0.05), which shows a range of evolutionary states, from quiescent to active. The gas properties were derived using radiative transfer modeling of the (1,1), (2,2), and (4,4) transitions of NH{sub 3} on the Karl G. Jansky Very Large Array, while the dust temperatures and column densities were calculated using cirrus-subtracted, modified blackbody fits to Herschel data. We compare the derived column densities to calculate an NH{sub 3} abundance, χ{sub NH{sub 3}} = 4.6 × 10{sup –8}. In the coldest star-forming region, we find that the measured dust temperatures are lower than the measured gas temperatures (mean and standard deviations T {sub dust,} {sub avg} ∼ 11.6 ± 0.2 K versus T {sub gas,} {sub avg} ∼ 15.2 ± 1.5 K), which may indicate that the gas and dust are not well-coupled in the youngest regions (∼0.5 Myr) or that these observations probe a regime where the dust and/or gas temperature measurements are unreliable. Finally, we calculate millimeter fluxes based on the temperatures and column densities derived from NH{sub 3}, which suggest that millimeter dust continuum observations of massive star-forming regions, such as the Bolocam Galactic Plane Survey or ATLASGAL, can probe hot cores, cold cores, and the dense gas lanes from which they form, and are generally not dominated by the hottest core.

The comparison of physical properties derived from gas and dust in a massive star-forming region

International Nuclear Information System (INIS)

Battersby, Cara; Bally, John; Ginsburg, Adam; Darling, Jeremy; Dunham, Miranda; Longmore, Steve

2014-01-01

We explore the relationship between gas and dust in a massive star-forming region by comparing the physical properties derived from each. We compare the temperatures and column densities in a massive star-forming Infrared Dark Cloud (G32.02+0.05), which shows a range of evolutionary states, from quiescent to active. The gas properties were derived using radiative transfer modeling of the (1,1), (2,2), and (4,4) transitions of NH 3 on the Karl G. Jansky Very Large Array, while the dust temperatures and column densities were calculated using cirrus-subtracted, modified blackbody fits to Herschel data. We compare the derived column densities to calculate an NH 3 abundance, χ NH 3 = 4.6 × 10 –8 . In the coldest star-forming region, we find that the measured dust temperatures are lower than the measured gas temperatures (mean and standard deviations T dust, avg ∼ 11.6 ± 0.2 K versus T gas, avg ∼ 15.2 ± 1.5 K), which may indicate that the gas and dust are not well-coupled in the youngest regions (∼0.5 Myr) or that these observations probe a regime where the dust and/or gas temperature measurements are unreliable. Finally, we calculate millimeter fluxes based on the temperatures and column densities derived from NH 3 , which suggest that millimeter dust continuum observations of massive star-forming regions, such as the Bolocam Galactic Plane Survey or ATLASGAL, can probe hot cores, cold cores, and the dense gas lanes from which they form, and are generally not dominated by the hottest core.

A RING/DISK/OUTFLOW SYSTEM ASSOCIATED WITH W51 NORTH: A VERY MASSIVE STAR IN THE MAKING

International Nuclear Information System (INIS)

Zapata, Luis A.; Schilke, Peter; Menten, Karl; Ho, Paul T. P.; Rodriguez, Luis F.; Palau, Aina; Garrod, Robin T.

2009-01-01

Sensitive and high angular resolution (∼0.''4) SO 2 [22 2,20 → 22 1,21 ] and SiO[5 → 4] line and 1.3 and 7 mm continuum observations made with the Submillimeter Array (SMA) and the Very Large Array (VLA) toward the young massive cluster W51 IRS2 are presented. We report the presence of a large (of about 3000 AU) and massive (40 M sun ) dusty circumstellar disk and a hot gas molecular ring around a high-mass protostar or a compact small stellar system associated with W51 North. The simultaneous observations of the silicon monoxide molecule, an outflow gas tracer, further revealed a massive (200 M sun ) and collimated (∼14 0 ) outflow nearly perpendicular to the dusty and molecular structures suggesting thus the presence of a single very massive protostar with a bolometric luminosity on the order of 10 5 L sun . A molecular hybrid local thermodynamic equilibrium model of a Keplerian and infalling disk with an inner cavity and a central stellar mass of more than 60 M sun agrees well with the SO 2 [22 2,20 → 22 1,21 ] line observations. Finally, these results suggest that mechanisms, such as mergers of low- and intermediate-mass stars, might not be necessary for forming very massive stars.

WR 148: identifying the companion of an extreme runaway massive binary*

Science.gov (United States)

Munoz, Melissa; Moffat, Anthony F. J.; Hill, Grant M.; Shenar, Tomer; Richardson, Noel D.; Pablo, Herbert; St-Louis, Nicole; Ramiaramanantsoa, Tahina

2017-05-01

WR 148 (HD 197406) is an extreme runaway system considered to be a potential candidate for a short-period (4.3173 d) rare WR + compact object binary. Provided with new high-resolution, high signal-to-noise spectra from the Keck observatory, we determine the orbital parameters for both the primary WR and the secondary, yielding respective projected orbital velocity amplitudes of 88.1 ± 3.8 km s-1 and 79.2 ± 3.1 km s-1 and implying a mass ratio of 1.1 ± 0.1. We then apply the shift-and-add technique to disentangle the spectra and obtain spectra compatible with a WN7ha and an O4-6 star. Considering an orbital inclination of ˜67°, derived from previous polarimetry observations, the system's total mass would be a mere 2-3M_{⊙}, an unprecedented result for a putative massive binary system. However, a system comprising a 37 M_{⊙} secondary (typical mass of an O5V star) and a 33 M_{⊙} primary (given the mass ratio) would infer an inclination of ˜18°. We therefore reconsider the previous methods of deriving the orbital inclination based on time-dependent polarimetry and photometry. While the polarimetric results are inconclusive requiring better data, the photometric results favour low inclinations. Finally, we compute WR 148's space velocity and retrace the runaway's trajectory back to the Galactic plane (GP). With an ejection velocity of 198 ± 27 km s-1 and a travel time of 4.7 ± 0.8 Myr to reach its current location, WR 148 was most likely ejected via dynamical interactions in a young cluster.

SPITZER SAGE-SMC INFRARED PHOTOMETRY OF MASSIVE STARS IN THE SMALL MAGELLANIC CLOUD

International Nuclear Information System (INIS)

Bonanos, A. Z.; Lennon, D. J.; Massa, D. L.

2010-01-01

We present a catalog of 5324 massive stars in the Small Magellanic Cloud (SMC), with accurate spectral types compiled from the literature, and a photometric catalog for a subset of 3654 of these stars, with the goal of exploring their infrared properties. The photometric catalog consists of stars with infrared counterparts in the Spitzer SAGE-SMC survey database, for which we present uniform photometry from 0.3to24 μm in the UBVIJHK s +IRAC+MIPS24 bands. We compare the color-magnitude diagrams and color-color diagrams to those of stars in the Large Magellanic Cloud (LMC), finding that the brightest infrared sources in the SMC are also the red supergiants, supergiant B[e] (sgB[e]) stars, luminous blue variables, and Wolf-Rayet stars, with the latter exhibiting less infrared excess, the red supergiants being less dusty and the sgB[e] stars being on average less luminous. Among the objects detected at 24 μm in the SMC are a few very luminous hypergiants, four B-type stars with peculiar, flat spectral energy distributions, and all three known luminous blue variables. We detect a distinct Be star sequence, displaced to the red, and suggest a novel method of confirming Be star candidates photometrically. We find a higher fraction of Oe and Be stars among O and early-B stars in our SMC catalog, respectively, when compared to the LMC catalog, and that the SMC Be stars occur at higher luminosities. We estimate mass-loss rates for the red supergiants, confirming the correlation with luminosity even at the metallicity of the SMC. Finally, we confirm the new class of stars displaying composite A and F type spectra, the sgB[e] nature of 2dFS1804 and find the F0 supergiant 2dFS3528 to be a candidate luminous blue variable with cold dust.

TOWARD COMPLETE STATISTICS OF MASSIVE BINARY STARS: PENULTIMATE RESULTS FROM THE CYGNUS OB2 RADIAL VELOCITY SURVEY

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Kobulnicky, Henry A.; Lundquist, Michael J.; Burke, Jamison; Chapman, James; Keller, Erica; Lester, Kathryn; Rolen, Emily K.; Topel, Eric; Bhattacharjee, Anirban; Smullen, Rachel A.; Álvarez, Carlos A. Vargas; Runnoe, Jessie C.; Dale, Daniel A.; Brotherton, Michael M. [Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82070 (United States); Kiminki, Daniel C., E-mail: chipk@uwyo.edu, E-mail: jburke2@swarthmore.edu, E-mail: jc6380@mcla.edu, E-mail: kelle22e@mtholyoke.edu, E-mail: kvl214@lehigh.edu, E-mail: emily.k.rolen@vanderbilt.edu, E-mail: topel@stolaf.edu [Department of Astronomy, University of Arizona, Tucson, AZ 85721 (United States)

2014-08-01

We analyze orbital solutions for 48 massive multiple-star systems in the Cygnus OB2 association, 23 of which are newly presented here, to find that the observed distribution of orbital periods is approximately uniform in log P for P < 45 days, but it is not scale-free. Inflections in the cumulative distribution near 6 days, 14 days, and 45 days suggest key physical scales of ≅0.2, ≅0.4, and ≅1 A.U. where yet-to-be-identified phenomena create distinct features. No single power law provides a statistically compelling prescription, but if features are ignored, a power law with exponent β ≅ –0.22 provides a crude approximation over P = 1.4-2000 days, as does a piece-wise linear function with a break near 45 days. The cumulative period distribution flattens at P > 45 days, even after correction for completeness, indicating either a lower binary fraction or a shift toward low-mass companions. A high degree of similarity (91% likelihood) between the Cyg OB2 period distribution and that of other surveys suggests that the binary properties at P ≲ 25 days are determined by local physics of disk/clump fragmentation and are relatively insensitive to environmental and evolutionary factors. Fully 30% of the unbiased parent sample is a binary with period P < 45 days. Completeness corrections imply a binary fraction near 55% for P < 5000 days. The observed distribution of mass ratios 0.2 < q < 1 is consistent with uniform, while the observed distribution of eccentricities 0.1 < e < 0.6 is consistent with uniform plus an excess of e ≅ 0 systems. We identify six stars, all supergiants, that exhibit aperiodic velocity variations of ∼30 km s{sup –1} attributed to atmospheric fluctuations.

International Deep Planet Survey, 317 stars to determine the wide-separated planet frequency

Science.gov (United States)

Galicher, R.; Marois, C.; Macintosh, B.; Zuckerman, B.; Song, I.; Barman, T.; Patience, J.

2013-09-01

Since 2000, more than 300 nearby young stars were observed for the International Deep Planet Survey with adaptive optics systems at Gemini (NIRI/NICI), Keck (Nirc2), and VLT (Naco). Massive young AF stars were included in our sample whereas they have generally been neglected in first generation surveys because the contrast and target distances are less favorable to image substellar companions. The most significant discovery of the campaign is the now well-known HR 8799 multi-planet system. This remarkable finding allows, for the first time, an estimate of the Jovians planet population at large separations (further than a few AUs) instead of deriving upper limits. During my presentation, I will present the survey showing images of multiple stars and planets. I will then propose a statistic study of the observed stars deriving constraints on the Jupiter-like planet frequency at large separations.

The GAPS Programme with HARPS-N at TNG. XV. A substellar companion around a K giant star identified with quasi-simultaneous HARPS-N and GIANO measurements

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González-Álvarez, E.; Affer, L.; Micela, G.; Maldonado, J.; Carleo, I.; Damasso, M.; D'Orazi, V.; Lanza, A. F.; Biazzo, K.; Poretti, E.; Gratton, R.; Sozzetti, A.; Desidera, S.; Sanna, N.; Harutyunyan, A.; Massi, F.; Oliva, E.; Claudi, R.; Cosentino, R.; Covino, E.; Maggio, A.; Masiero, S.; Molinari, E.; Pagano, I.; Piotto, G.; Smareglia, R.; Benatti, S.; Bonomo, A. S.; Borsa, F.; Esposito, M.; Giacobbe, P.; Malavolta, L.; Martinez-Fiorenzano, A.; Nascimbeni, V.; Pedani, M.; Rainer, M.; Scandariato, G.

2017-10-01

Context. Identification of planetary companions of giant stars is made difficult because of the astrophysical noise, that may produce radial velocity variations similar to those induced by a companion. On the other hand any stellar signal is wavelength dependent, while signals due to a companion are achromatic. Aims: Our goal is to determine the origin of the Doppler periodic variations observed in the thick disk K giant star TYC 4282-605-1 by HARPS-N at the Telescopio Nazionale Galileo (TNG) and verify if they can be due to the presence of a substellar companion. Methods: Several methods have been used to exclude the stellar origin of the observed signal including detailed analysis of activity indicators and bisector and the analysis of the photometric light curve. Finally we have conducted an observational campaign to monitor the near infrared (NIR) radial velocity with GIANO at the TNG in order to verify whether the NIR amplitude variations are comparable with those observed in the visible. Results: Both optical and NIR radial velocities show consistent variations with a period at 101 days and similar amplitude, pointing to the presence of a companion orbiting the target. The main orbital properties obtained for our giant star with a derived mass of M = 0.97 ± 0.03M⊙ are MPsini = 10.78 ± 0.12MJ; P = 101.54 ± 0.05 days; e = 0.28 ± 0.01 and a = 0.422 ± 0.009 AU. The chemical analysis shows a significant enrichment in the abundance of Na I, Mg I, Al I and Si I while the rest of analyzed elements are consistent with the solar value demonstrating that the chemical composition corresponds with an old K giant (age = 10.1 Gyr) belonging to local thick disk. Conclusions: We conclude that the substellar companion hypothesis for this K giant is the best explanation for the observed periodic radial velocity variation. This study also shows the high potential of multi-wavelength radial velocity observations for the validation of planet candidates. Based on

Modeling UV Radiation Feedback from Massive Stars. II. Dispersal of Star-forming Giant Molecular Clouds by Photoionization and Radiation Pressure

Science.gov (United States)

Kim, Jeong-Gyu; Kim, Woong-Tae; Ostriker, Eve C.

2018-05-01

UV radiation feedback from young massive stars plays a key role in the evolution of giant molecular clouds (GMCs) by photoevaporating and ejecting the surrounding gas. We conduct a suite of radiation hydrodynamic simulations of star cluster formation in marginally bound, turbulent GMCs, focusing on the effects of photoionization and radiation pressure on regulating the net star formation efficiency (SFE) and cloud lifetime. We find that the net SFE depends primarily on the initial gas surface density, Σ0, such that the SFE increases from 4% to 51% as Σ0 increases from 13 to 1300 {M}ȯ {pc}}-2. Cloud destruction occurs within 2–10 Myr after the onset of radiation feedback, or within 0.6–4.1 freefall times (increasing with Σ0). Photoevaporation dominates the mass loss in massive, low surface density clouds, but because most photons are absorbed in an ionization-bounded Strömgren volume, the photoevaporated gas fraction is proportional to the square root of the SFE. The measured momentum injection due to thermal and radiation pressure forces is proportional to {{{Σ }}}0-0.74, and the ejection of neutrals substantially contributes to the disruption of low mass and/or high surface density clouds. We present semi-analytic models for cloud dispersal mediated by photoevaporation and by dynamical mass ejection, and show that the predicted net SFE and mass loss efficiencies are consistent with the results of our numerical simulations.

The evolution of massive stars with mass loss: the H- and the He-burning phases

International Nuclear Information System (INIS)

Chieffi, Alessandro; Limongi, Marco

2010-01-01

The evolution of a massive star to its final fate is strongly modified by the efficient mass loss episodes it experiences during its lifetime. In the following, we will briefly summarize how the H- and the He- burning phases depend on the adopted mass loss rate.

Does the chemical signature of TYC 8442-1036-1 originate from a rotating massive star that died in a faint explosion?

Science.gov (United States)

Cescutti, G.; Valentini, M.; François, P.; Chiappini, C.; Depagne, E.; Christlieb, N.; Cortés, C.

2016-11-01

Context. We have recently investigated the origin of chemical signatures observed in Galactic halo stars by means of a stochastic chemical evolution model. We found that rotating massive stars are a promising way to explain several signatures observed in these fossil stars. Aims: We discuss how the extremely metal-poor halo star TYC 8442-1036-1, for which we have now obtained detailed abundances from VLT-UVES spectra, fits into the framework of our previous work. Methods: We applied a standard one-dimensional (1D) LTE analysis to the spectrum of this star. We measured the abundances of 14 chemical elements; we computed the abundances for Na, Mg, Ca, Sc, Ti, V, Cr, Mn, Fe, Ni, and Zn using equivalent widths; we obtained the abundances for C, Sr, and Ba by means of synthetic spectra generated by MOOG. Results: We find an abundance of [Fe/H] = -3.5 ±0.13 dex based on our high-resolution spectrum; this points to an iron content that is lower by a factor of three (0.5 dex) compared to that obtained by a low-resolution spectrum. The star has a [C/Fe] = 0.4 dex, and it is not carbon enhanced like most of the stars at this metallicity. Moreover, this star lies in the plane [Ba/Fe] versus [Fe/H] in a relatively unusual position, shared by a few other Galactic halo stars, which is only marginally explained by our past results. Conclusions: The comparison of the model results with the chemical abundance characteristics of this group of stars can be improved if we consider in our model the presence of faint supernovae coupled with rotating massive stars. These results seem to imply that rotating massive stars and faint supernovae scenarios are complementary to each other, and are both required in order to match the observed chemistry of the earliest phases of the chemical enrichment of the Universe. Based on observations made with the ESO Very Large Telescope at Paranal Observatory, Chile (ID 094.B-0781(A); P.I. G. Cescutti).

A combined HST and XMM-Newton campaign for the magnetic O9.7 V star HD 54879. Constraining the weak-wind problem of massive stars

Science.gov (United States)

Shenar, T.; Oskinova, L. M.; Järvinen, S. P.; Luckas, P.; Hainich, R.; Todt, H.; Hubrig, S.; Sander, A. A. C.; Ilyin, I.; Hamann, W.-R.

2017-10-01

Context. HD 54879 (O9.7 V) is one of a dozen O-stars for which an organized atmospheric magnetic field has been detected. Despite their importance, little is known about the winds and evolution of magnetized massive stars. Aims: To gain insights into the interplay between atmospheres, winds, and magnetic fields of massive stars, we acquired UV and X-ray data of HD 54879 using the Hubble Space Telescope and the XMM-Newton satellite. In addition, 35 optical amateur spectra were secured to study the variability of HD 54879. Methods: A multiwavelength (X-ray to optical) spectral analysis is performed using the Potsdam Wolf-Rayet (PoWR) model atmosphere code and the xspec software. Results: The photospheric parameters (T∗ = 30.5 kK, log g = 4.0 [cm s-2], log L = 4.45 [L⊙]) are typical for an O9.7 V star. The microturbulent, macroturbulent, and projected rotational velocities are lower than previously suggested (ξph,vmac,vsini ≤ 4 km s-1). An initial mass of 16 M⊙ and an age of 5 Myr are inferred from evolutionary tracks. We derive a mean X-ray emitting temperature of log TX = 6.7 [K] and an X-ray luminosity of LX = 1 × 1032 erg s-1. Short- and long-scale variability is seen in the Hα line, but only a very long period of P ≈ 5 yr could be estimated. Assessing the circumstellar density of HD 54879 using UV spectra, we can roughly estimate the mass-loss rate HD 54879 would have in the absence of a magnetic field as log ṀB = 0 ≈ -9.0 [M⊙ yr-1]. The magnetic field traps the stellar wind up to the Alfvén radius rA ≳ 12 R∗, implying that its true mass-loss rate is log Ṁ ≲ -10.2 [M⊙ yr-1]. Hence, density enhancements around magnetic stars can be exploited to estimate mass-loss rates of non-magnetic stars of similar spectral types, essential for resolving the weak wind problem. Conclusions: Our study confirms that strongly magnetized stars lose little or no mass, and supplies important constraints on the weak-wind problem of massive main sequence

On the Weak-Wind Problem in Massive Stars: X-Ray Spectra Reveal a Massive Hot Wind in mu Columbae

Science.gov (United States)

Huenemoerder, David P.; Oskinova, Lidia M.; Ignace, Richard; Waldron, Wayne L.; Todt, Helge; Hamaguchi, Kenji; Kitamoto, Shunji

2012-01-01

Mu Columbae is a prototypical weak-wind O star for which we have obtained a high-resolution X-ray spectrum with the Chandra LETG/ACIS instrument and a low-resolution spectrum with Suzaku. This allows us, for the first time, to investigate the role of X-rays on the wind structure in a bona fide weak-wind system and to determine whether there actually is a massive hot wind. The X-ray emission measure indicates that the outflow is an order of magnitude greater than that derived from UV lines and is commensurate with the nominal wind-luminosity relationship for O stars. Therefore, the "weak-wind problem"--identified from cool wind UV/optical spectra--is largely resolved by accounting for the hot wind seen in X-rays. From X-ray line profiles, Doppler shifts, and relative strengths, we find that this weak-wind star is typical of other late O dwarfs. The X-ray spectra do not suggest a magnetically confined plasma-the spectrum is soft and lines are broadened; Suzaku spectra confirm the lack of emission above 2 keV. Nor do the relative line shifts and widths suggest any wind decoupling by ions. The He-like triplets indicate that the bulk of the X-ray emission is formed rather close to the star, within five stellar radii. Our results challenge the idea that some OB stars are "weak-wind" stars that deviate from the standard wind-luminosity relationship. The wind is not weak, but it is hot and its bulk is only detectable in X-rays.

Tables and intercomparisons of evolutionary sequences of models for massive stars

International Nuclear Information System (INIS)

Chin, Chaowen; Stothers, R.B.

1990-01-01

Tables of evolutionary sequences of models for massive stars have been prepared for a variety of physical input parameters that are normally treated as free. These parameters include the interior convective mixing scheme, the mixing length in the outer convective envelope, the rate of stellar-wind mass loss, the initial stellar mass, and the initial chemical composition. Ranges of specified initial mass and initial chemical composition are M = 10-120 solar masses, Xe = 0.602-0.739, and Ze = 0.021-0.044. The tables cover evolution of the star from the ZAMS to either the end of core H burning or the end of core He burning. Differences among the evolutionary tracks are illustrated primarily in terms of the interior mixing scheme, since the amount and timing of stellar wind mass loss are still very uncertain for initial masses above about 30 solar masses. 52 refs

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.

Stellar neutron sources and s-process in massive stars

Science.gov (United States)

Talwar, Rashi

The s-process or the slow neutron capture process is a nucleosynthesis process taking place at relatively low neutron densities in stars. It runs along the valley of beta stability since the neutron capture rate is much slower compared to the beta decay rate. The s-process occurs mainly during core helium burning and shell carbon burning phase in massive stars and during thermally pulsing helium burning phase in asymptotic giant-branch stars. The potential stellar neutron source for the s-process is associated with alpha-capture reactions on light nuclei. The capture-reaction rates provide the reaction flow for the build-up of22Ne neutron source during the heliumburning phase in these stars. The low energy 26Mg resonances at stellar energies below 800 keV are predicted to have a critical influence on the alpha-capture rates on 22Ne. Some of these resonances may also correspond to pronounced alpha cluster structure near the alpha-threshold. However, these resonances have remained elusive during direct alpha capture measurements owing to the high Coulomb barrier and background from cosmic rays and beam induced reactions. Hence, in the present work, alpha-inelastic scattering and alpha- transfer measurements have been performed to probe the level structure of 26Mg nucleus in order to determine the 22Ne+alpha-capture rates. Both experiments have been performed using the high-resolution Grand Raiden Spectrometer at the Research Center for Nuclear Physics (RCNP), Osaka, Japan. For the alpha-inelastic scattering measurement, a self-supporting solid 26Mg target was used and for the alpha-transfer study via the (6Li,d) reaction, 22Ne gas enclosed in a gas cell with Aramid windows was used. The reaction products were momentum analysed by the spectrometer and detected at the focal plane equipped with two multi-wire drift chambers and two plastic-scintillation detectors. The focal plane detection system provided information on the position, the angle, the time of flight and

Search for OB stars running away from young star clusters. II. The NGC 6357 star-forming region

Science.gov (United States)

Gvaramadze, V. V.; Kniazev, A. Y.; Kroupa, P.; Oh, S.

2011-11-01

Dynamical few-body encounters in the dense cores of young massive star clusters are responsible for the loss of a significant fraction of their massive stellar content. Some of the escaping (runaway) stars move through the ambient medium supersonically and can be revealed via detection of their bow shocks (visible in the infrared, optical or radio). In this paper, which is the second of a series of papers devoted to the search for OB stars running away from young ( ≲ several Myr) Galactic clusters and OB associations, we present the results of the search for bow shocks around the star-forming region NGC 6357. Using the archival data of the Midcourse Space Experiment (MSX) satellite and the Spitzer Space Telescope, and the preliminary data release of the Wide-Field Infrared Survey Explorer (WISE), we discovered seven bow shocks, whose geometry is consistent with the possibility that they are generated by stars expelled from the young (~1-2 Myr) star clusters, Pismis 24 and AH03 J1725-34.4, associated with NGC 6357. Two of the seven bow shocks are driven by the already known OB stars, HD 319881 and [N78] 34. Follow-up spectroscopy of three other bow-shock-producing stars showed that they are massive (O-type) stars as well, while the 2MASS photometry of the remaining two stars suggests that they could be B0 V stars, provided that both are located at the same distance as NGC 6357. Detection of numerous massive stars ejected from the very young clusters is consistent with the theoretical expectation that star clusters can effectively lose massive stars at the very beginning of their dynamical evolution (long before the second mechanism for production of runaway stars, based on a supernova explosion in a massive tight binary system, begins to operate) and lends strong support to the idea that probably all field OB stars have been dynamically ejected from their birth clusters. A by-product of our search for bow shocks around NGC 6357 is the detection of three circular

PLANETS AROUND LOW-MASS STARS (PALMS). I. A SUBSTELLAR COMPANION TO THE YOUNG M DWARF 1RXS J235133.3+312720

Energy Technology Data Exchange (ETDEWEB)

Bowler, Brendan P.; Liu, Michael C.; Cieza, Lucas A.; Kraus, Adam L. [Institute for Astronomy, University of Hawai' i, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Shkolnik, Evgenya L. [Lowell Observatory, 1400 W. Mars Hill Road, Flagstaff, AZ 86001 (United States); Dupuy, Trent J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Tamura, Motohide, E-mail: bpbowler@ifa.hawaii.edu [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)

2012-07-10

We report the discovery of a brown dwarf companion to the young M dwarf 1RXS J235133.3+312720 as part of a high contrast imaging search for planets around nearby young low-mass stars with Keck-II/NIRC2 and Subaru/HiCIAO. The 2.''4 ({approx}120 AU) pair is confirmed to be comoving from two epochs of high-resolution imaging. Follow-up low- and moderate-resolution near-infrared spectroscopy of 1RXS J2351+3127 B with IRTF/SpeX and Keck-II/OSIRIS reveals a spectral type of L0{sup +2}{sub -1}. The M2 primary star 1RXS J2351+3127 A exhibits X-ray and UV activity levels comparable to young moving group members with ages of {approx}10-100 Myr. UVW kinematics based the measured radial velocity of the primary and the system's photometric distance (50 {+-} 10 pc) indicate it is likely a member of the {approx}50-150 Myr AB Dor moving group. The near-infrared spectrum of 1RXS J2351+3127 B does not exhibit obvious signs of youth, but its H-band morphology shows subtle hints of intermediate surface gravity. The spectrum is also an excellent match to the {approx}200 Myr M9 brown dwarf LP 944-20. Assuming an age of 50-150 Myr, evolutionary models imply a mass of 32 {+-} 6 M{sub Jup} for the companion, making 1RXS J2351+3127 B the second lowest-mass member of the AB Dor moving group after the L4 companion CD-35 2722 B and one of the few benchmark brown dwarfs known at young ages.

THE PALOMAR/KECK ADAPTIVE OPTICS SURVEY OF YOUNG SOLAR ANALOGS: EVIDENCE FOR A UNIVERSAL COMPANION MASS FUNCTION

International Nuclear Information System (INIS)

Metchev, Stanimir A.; Hillenbrand, Lynne A.

2009-01-01

We present results from an adaptive optics survey for substellar and stellar companions to Sun-like stars. The survey targeted 266 F5-K5 stars in the 3 Myr-3 Gyr age range with distances of 10-190 pc. Results from the survey include the discovery of two brown dwarf companions (HD 49197B and HD 203030B), 24 new stellar binaries, and a triple system. We infer that the frequency of 0.012-0.072 M sun brown dwarfs in 28-1590 AU orbits around young solar analogs is 3.2 +3.1 -2.7 % (2σ limits). The result demonstrates that the deficiency of substellar companions at wide orbital separations from Sun-like stars is less pronounced than in the radial velocity 'brown dwarf desert'. We infer that the mass distribution of companions in 28-1590 AU orbits around solar-mass stars follows a continuous dN/dM 2 ∝ M -0.4 2 relation over the 0.01-1.0 M sun secondary mass range. While this functional form is similar to that for isolated objects less than 0.1 M sun , over the entire 0.01-1.0 M sun range, the mass functions of companions and of isolated objects differ significantly. Based on this conclusion and on similar results from other direct imaging and radial velocity companion surveys in the literature, we argue that the companion mass function follows the same universal form over the entire range between 0 and 1590 AU in orbital semimajor axis and ∼ 0.01-20 M sun in companion mass. In this context, the relative dearth of substellar versus stellar secondaries at all orbital separations arises naturally from the inferred form of the companion mass function.

Age gradients in the stellar populations of massive star forming regions based on a new stellar chronometer

Energy Technology Data Exchange (ETDEWEB)

Getman, Konstantin V.; Feigelson, Eric D.; Kuhn, Michael A.; Broos, Patrick S.; Townsley, Leisa K.; Luhman, Kevin L. [Department of Astronomy and Astrophysics, 525 Davey Laboratory, Pennsylvania State University, University Park, PA 16802 (United States); Naylor, Tim [School of Physics and Astronomy, University of Exeter, Stocker Road, Exeter, EX4 4QL (United Kingdom); Povich, Matthew S. [Department of Physics and Astronomy, California State Polytechnic University, 3801 West Temple Avenue, Pomona, CA 91768 (United States); Garmire, Gordon P. [Huntingdon Institute for X-ray Astronomy, LLC, 10677 Franks Road, Huntingdon, PA 16652 (United States)

2014-06-01

A major impediment to understanding star formation in massive star-forming regions (MSFRs) is the absence of a reliable stellar chronometer to unravel their complex star formation histories. We present a new estimation of stellar ages using a new method that employs near-infrared (NIR) and X-ray photometry, Age {sub JX} . Stellar masses are derived from X-ray luminosities using the L{sub X} -M relation from the Taurus cloud. J-band luminosities are compared to mass-dependent pre-main-sequence (PMS) evolutionary models to estimate ages. Age {sub JX} is sensitive to a wide range of evolutionary stages, from disk-bearing stars embedded in a cloud to widely dispersed older PMS stars. The Massive Young Star-Forming Complex Study in Infrared and X-ray (MYStIX) project characterizes 20 OB-dominated MSFRs using X-ray, mid-infrared, and NIR catalogs. The Age {sub JX} method has been applied to 5525 out of 31,784 MYStIX Probable Complex Members. We provide a homogeneous set of median ages for over 100 subclusters in 15 MSFRs; median subcluster ages range between 0.5 Myr and 5 Myr. The important science result is the discovery of age gradients across MYStIX regions. The wide MSFR age distribution appears as spatially segregated structures with different ages. The Age {sub JX} ages are youngest in obscured locations in molecular clouds, intermediate in revealed stellar clusters, and oldest in distributed populations. The NIR color index J – H, a surrogate measure of extinction, can serve as an approximate age predictor for young embedded clusters.

The SOFIA Massive (SOMA) Star Formation Survey. I. Overview and First Results

Energy Technology Data Exchange (ETDEWEB)

De Buizer, James M.; Shuping, Ralph [SOFIA-USRA, NASA Ames Research Center, MS 232-12, Moffett Field, CA 94035 (United States); Liu, Mengyao; Tan, Jonathan C.; Staff, Jan E.; Tanaka, Kei E. I. [Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States); Zhang, Yichen [Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago (Chile); Beltrán, Maria T. [INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze (Italy); Whitney, Barbara [Department of Astronomy, University of Wisconsin-Madison, 475 N. Charter St, Madison, WI 53706 (United States)

2017-07-01

We present an overview and first results of the Stratospheric Observatory For Infrared Astronomy Massive (SOMA) Star Formation Survey, which is using the FORCAST instrument to image massive protostars from ∼10 to 40 μ m. These wavelengths trace thermal emission from warm dust, which in Core Accretion models mainly emerges from the inner regions of protostellar outflow cavities. Dust in dense core envelopes also imprints characteristic extinction patterns at these wavelengths, causing intensity peaks to shift along the outflow axis and profiles to become more symmetric at longer wavelengths. We present observational results for the first eight protostars in the survey, i.e., multiwavelength images, including some ancillary ground-based mid-infrared (MIR) observations and archival Spitzer and Herschel data. These images generally show extended MIR/FIR emission along directions consistent with those of known outflows and with shorter wavelength peak flux positions displaced from the protostar along the blueshifted, near-facing sides, thus confirming qualitative predictions of Core Accretion models. We then compile spectral energy distributions and use these to derive protostellar properties by fitting theoretical radiative transfer models. Zhang and Tan models, based on the Turbulent Core Model of McKee and Tan, imply the sources have protostellar masses m {sub *} ∼ 10–50 M {sub ⊙} accreting at ∼10{sup −4}–10{sup −3} M {sub ⊙} yr{sup −1} inside cores of initial masses M {sub c} ∼ 30–500 M {sub ⊙} embedded in clumps with mass surface densities Σ{sub cl} ∼ 0.1–3 g cm{sup −2}. Fitting the Robitaille et al. models typically leads to slightly higher protostellar masses, but with disk accretion rates ∼100× smaller. We discuss reasons for these differences and overall implications of these first survey results for massive star formation theories.

Binary progenitors of supernovae

Science.gov (United States)

Trimble, V.

1984-12-01

Among the massive stars that are expected to produce Type II, hydrogen-rich supernovae, the presence of a close companion can increase the main sequence mass needed to yield a collapsing core. In addition, due to mass transfer from the primary to the secondary, the companion enhances the stripping of the stellar hydrogen envelope produced by single star winds and thereby makes it harder for the star to give rise to a typical SN II light curve. Among the less massive stars that may be the basis for Type I, hydrogen-free supernovae, a close companion could be an innocent bystander to carbon detonation/deflagration in the primary. It may alternatively be a vital participant which transfers material to a white dwarf primary and drives it to explosive conditions.

VERY-LOW-MASS STELLAR AND SUBSTELLAR COMPANIONS TO SOLAR-LIKE STARS FROM MARVELS. III. A SHORT-PERIOD BROWN DWARF CANDIDATE AROUND AN ACTIVE G0IV SUBGIANT

Energy Technology Data Exchange (ETDEWEB)

Ma Bo; Ge Jian; De Lee, Nathan; Fleming, Scott W.; Lee, Brian L.; Wang Ji [Department of Astronomy, University of Florida, 211 Bryant Space Science Center, Gainesville, FL 32611-2055 (United States); Barnes, Rory; Agol, Eric [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195-1580 (United States); Crepp, Justin R. [Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Dutra-Ferreira, Leticia; Porto de Mello, G. F. [Observatorio do Valongo, Universidade Federal do Rio de Janeiro, Ladeira do Pedro Antonio, 43, CEP: 20080-090, Rio de Janeiro, RJ (Brazil); Esposito, Massimiliano; Femenia, Bruno; Gonzalez Hernandez, Jonay I. [Instituto de Astrofisica de Canarias, C/Via Lctea S/N, E-38200 La Laguna (Spain); Gaudi, B. Scott [Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States); Ghezzi, Luan [Laboratorio Interinstitucional de e-Astronomia (LIneA), Rio de Janeiro, RJ 20921-400 (Brazil); Hebb, Leslie; Stassun, Keivan G. [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States); Wisniewski, John P. [Homer L Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W Brooks St, Norman, OK 73019 (United States); Bizyaev, Dmitry, E-mail: boma@astro.ufl.edu [Apache Point Observatory, P.O. Box 59, Sunspot, NM 88349-0059 (United States); and others

2013-01-01

We present an eccentric, short-period brown dwarf candidate orbiting the active, slightly evolved subgiant star TYC 2087-00255-1, which has effective temperature T{sub eff} = 5903 {+-} 42 K, surface gravity log (g) = 4.07 {+-} 0.16 (cgs), and metallicity [Fe/H] = -0.23 {+-} 0.07. This candidate was discovered using data from the first two years of the Multi-object APO Radial Velocity Exoplanets Large-area Survey, which is part of the third phase of Sloan Digital Sky Survey. From our 38 radial velocity measurements spread over a two-year time baseline, we derive a Keplerian orbital fit with semi-amplitude K = 3.571 {+-} 0.041 km s{sup -1}, period P = 9.0090 {+-} 0.0004 days, and eccentricity e = 0.226 {+-} 0.011. Adopting a mass of 1.16 {+-} 0.11 M{sub Sun} for the subgiant host star, we infer that the companion has a minimum mass of 40.0 {+-} 2.5 M{sub Jup}. Assuming an edge-on orbit, the semimajor axis is 0.090 {+-} 0.003 AU. The host star is photometrically variable at the {approx}1% level with a period of {approx}13.16 {+-} 0.01 days, indicating that the host star spin and companion orbit are not synchronized. Through adaptive optics imaging we also found a point source 643 {+-} 10 mas away from TYC 2087-00255-1, which would have a mass of 0.13 M{sub Sun} if it is physically associated with TYC 2087-00255-1 and has the same age. Future proper motion observation should be able to resolve if this tertiary object is physically associated with TYC 2087-00255-1 and make TYC 2087-00255-1 a triple body system. Core Ca II H and K line emission indicate that the host is chromospherically active, at a level that is consistent with the inferred spin period and measured v{sub rot}sin i, but unusual for a subgiant of this T{sub eff}. This activity could be explained by ongoing tidal spin-up of the host star by the companion.

Hyper-massive cloud, shock and stellar formation efficiency

International Nuclear Information System (INIS)

Louvet, Fabien

2014-01-01

O and B types stars are of paramount importance in the energy budget of galaxies and play a crucial role enriching the interstellar medium. However, their formation, unlike that of solar-type stars, is still subject to debate, if not an enigma. The earliest stages of massive star formation and the formation of their parent cloud are still crucial astrophysical questions that drew a lot of attention in the community, both from the theoretical and observational perspective, during the last decade. It has been proposed that massive stars are born in massive dense cores that form through very dynamic processes, such as converging flows of gas. During my PhD, I conducted a thorough study of the formation of dense cores and massive stars in the W43-MM1 supermassive structure, located at 6 kpc from the sun. At first, I showed a direct correlation between the star formation efficiency and the volume gas density of molecular clouds, in contrast with scenarios suggested by previous studies. Indeed, the spatial distribution and mass function of the massive dense cores currently forming in W43-MM1 suggests that this supermassive filament is undergoing a star formation burst, increasing as one approaches its center. I compared these observational results with the most recent numerical and analytical models of star formation. This comparison not only provides new constraints on the formation of supermassive filaments, but also suggests that understanding star formation in high density, extreme ridges requires a detailed portrait of the structure of these exceptional objects. Second, having shown that the formation of massive stars depends strongly on the properties of the ridges where they form, I studied the formation processes of these filaments, thanks of the characterization of their global dynamics. Specifically, I used a tracer of shocks (SiO molecule) to disentangle the feedback of local star formation processes (bipolar jets and outflows) from shocks tracing the pristine

Resolved Companions of Cepheids as Seen by HST and XMM

Science.gov (United States)

Evans, Nancy Remage; Bond, Howard E.; Schaefer, Gail; Mason, Brian D.; Tingle, Evan; Karovska, Margarita; Pillitteri, Ignazio; Wolk, Scott J.; Guinan, Edward F.; Engle, Scott G.

2016-01-01

We have conducted a survey of 70 classical Cepheids with the Hubble Wide Field Camera3 (WFC3) to identify possible resolved companions. Data cover the range of 0.3" to 20" which typically corresponds to 200 AU to 0.1 pc. At present only possible companions greater than 5" from the Cepheid are discussed, since closer companions require a sophisticated point spread correction for the light of the much brighter Cepheid. We have followed up a subset of the possible resolved companions with XMM observations to determine whether they are young (X-ray active) enough to be physical companions of the Cepheids. We estimate that 4% of the Cepheids have a physical resolved companion, with the widest having a separation of 4000 AU. The one wider young star is in the field of S Nor, but since it is a cluster member, the companion is not assumed to be gravitationally bound to the Cepheid.

Close Companions to Two High-redshift Quasars

Science.gov (United States)

McGreer, Ian D.; Fan, Xiaohui; Strauss, Michael A.; Haiman, Zoltàn; Richards, Gordon T.; Jiang, Linhua; Bian, Fuyan; Schneider, Donald P.

2014-10-01

We report the serendipitous discoveries of companion galaxies to two high-redshift quasars. SDSS J025617.7+001904 is a z = 4.79 quasar included in our recent survey of faint quasars in the SDSS Stripe 82 region. The initial MMT slit spectroscopy shows excess Lyα emission extending well beyond the quasar's light profile. Further imaging and spectroscopy with LBT/MODS1 confirms the presence of a bright galaxy (i AB = 23.6) located 2'' (12 kpc projected) from the quasar with strong Lyα emission (EW0 ≈ 100 Å) at the redshift of the quasar, as well as faint continuum. The second quasar, CFHQS J005006.6+344522 (z = 6.25), is included in our recent HST SNAP survey of z ~ 6 quasars searching for evidence of gravitational lensing. Deep imaging with ACS and WFC3 confirms an optical dropout ~4.5 mag fainter than the quasar (Y AB = 25) at a separation of 0.''9. The red i 775 - Y 105 color of the galaxy and its proximity to the quasar (5 kpc projected if at the quasar redshift) strongly favor an association with the quasar. Although it is much fainter than the quasar, it is remarkably bright when compared to field galaxies at this redshift, while showing no evidence for lensing. Both systems may represent late-stage mergers of two massive galaxies, with the observed light for one dominated by powerful ongoing star formation and for the other by rapid black hole growth. Observations of close companions are rare; if major mergers are primarily responsible for high-redshift quasar fueling then the phase when progenitor galaxies can be observed as bright companions is relatively short. Based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs #12184 and #12493. Observations were also made with the LBT and MMT.

Triple system HD 201433 with a SPB star component seen by BRITE - Constellation: Pulsation, differential rotation, and angular momentum transfer

Science.gov (United States)

Kallinger, T.; Weiss, W. W.; Beck, P. G.; Pigulski, A.; Kuschnig, R.; Tkachenko, A.; Pakhomov, Y.; Ryabchikova, T.; Lüftinger, T.; Palle, , P. L.; Semenko, E.; Handler, G.; Koudelka, O.; Matthews, J. M.; Moffat, A. F. J.; Pablo, H.; Popowicz, A.; Rucinski, S.; Wade, G. A.; Zwintz, K.

2017-07-01

Context. Stellar rotation affects the transport of chemical elements and angular momentum and is therefore a key process during stellar evolution, which is still not fully understood. This is especially true for massive OB-type stars, which are important for the chemical enrichment of the Universe. It is therefore important to constrain the physical parameters and internal angular momentum distribution of massive OB-type stars to calibrate stellar structure and evolution models. Stellar internal rotation can be probed through asteroseismic studies of rotationally split non radial oscillations but such results are still quite rare, especially for stars more massive than the Sun. The slowly pulsating B9V star HD 201433 is known to be part of a single-lined spectroscopic triple system, with two low-mass companions orbiting with periods of about 3.3 and 154 days. Aims: Our goal is to measure the internal rotation profile of HD 201433 and investigate the tidal interaction with the close companion. Methods: We used probabilistic methods to analyse the BRITE - Constellation photometry and radial velocity measurements, to identify a representative stellar model, and to determine the internal rotation profile of the star. Results: Our results are based on photometric observations made by BRITE - Constellation and the Solar Mass Ejection Imager on board the Coriolis satellite, high-resolution spectroscopy, and more than 96 yr of radial velocity measurements. We identify a sequence of nine frequency doublets in the photometric time series, consistent with rotationally split dipole modes with a period spacing of about 5030 s. We establish that HD 201433 is in principle a solid-body rotator with a very slow rotation period of 297 ± 76 days. Tidal interaction with the inner companion has, however, significantly accelerated the spin of the surface layers by a factor of approximately one hundred. The angular momentum transfer onto the surface of HD 201433 is also reflected by the

Kinetic temperature of massive star forming molecular clumps measured with formaldehyde

Science.gov (United States)

Tang, X. D.; Henkel, C.; Menten, K. M.; Zheng, X. W.; Esimbek, J.; Zhou, J. J.; Yeh, C. C.; König, C.; Yuan, Y.; He, Y. X.; Li, D. L.

2017-02-01

Context. For a general understanding of the physics involved in the star formation process, measurements of physical parameters such as temperature and density are indispensable. The chemical and physical properties of dense clumps of molecular clouds are strongly affected by the kinetic temperature. Therefore, this parameter is essential for a better understanding of the interstellar medium. Formaldehyde, a molecule which traces the entire dense molecular gas, appears to be the most reliable tracer to directly measure the gas kinetic temperature. Aims: We aim to determine the kinetic temperature with spectral lines from formaldehyde and to compare the results with those obtained from ammonia lines for a large number of massive clumps. Methods: Three 218 GHz transitions (JKAKC = 303-202, 322-221, and 321-220) of para-H2CO were observed with the 15 m James Clerk Maxwell Telescope (JCMT) toward 30 massive clumps of the Galactic disk at various stages of high-mass star formation. Using the RADEX non-LTE model, we derive the gas kinetic temperature modeling the measured para-H2CO 322-221/303-202 and 321-220/303-202 ratios. Results: The gas kinetic temperatures derived from the para-H2CO (321-220/303-202) line ratios range from 30 to 61 K with an average of 46 ± 9 K. A comparison of kinetic temperature derived from para-H2CO, NH3, and the dust emission indicates that in many cases para-H2CO traces a similar kinetic temperature to the NH3 (2, 2)/(1, 1) transitions and the dust associated with the HII regions. Distinctly higher temperatures are probed by para-H2CO in the clumps associated with outflows/shocks. Kinetic temperatures obtained from para-H2CO trace turbulence to a higher degree than NH3 (2, 2)/(1, 1) in the massive clumps. The non-thermal velocity dispersions of para-H2CO lines are positively correlated with the gas kinetic temperature. The massive clumps are significantly influenced by supersonic non-thermal motions. The reduced spectra (FITS files) are only

CAUGHT IN THE ACT: THE ASSEMBLY OF MASSIVE CLUSTER GALAXIES AT z = 1.62

International Nuclear Information System (INIS)

Lotz, Jennifer M.; Ferguson, Henry C.; Grogin, Norman; Koekemoer, Anton M.; Papovich, Casey; Tran, Kim-Vy; Faber, S. M.; Guo Yicheng; Kocevski, Dale; Lee, Kyoung-Soo; McIntosh, Daniel; Momcheva, Ivelina; Rudnick, Gregory; Saintonge, Amelie; Van der Wel, Arjen; Willmer, Christopher

2013-01-01

We present the recent merger history of massive galaxies in a spectroscopically confirmed proto-cluster at z = 1.62. Using Hubble Space Telescope WFC3 near-infrared imaging from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey, we select cluster and z ∼ 1.6 field galaxies with M star ≥ 3 × 10 10 M ☉ , to determine the frequency of double nuclei or close companions within projected separations less than 20 kpc co-moving. We find that four out of five spectroscopically confirmed massive proto-cluster galaxies have double nuclei, and 57 +13 -14 % of all M star ≥ 3 × 10 10 M ☉ cluster candidates are observed in either close pair systems or have double nuclei. In contrast, only 11% ± 3% of the field galaxies are observed in close pair/double nuclei systems. After correcting for the contribution from random projections, the implied merger rate per massive galaxy in the proto-cluster is ∼3-10 times higher than the merger rate of massive field galaxies at z ∼ 1.6. Close pairs in the cluster have minor merger stellar mass ratios (M primary : M satellite ≥ 4), while the field pairs consist of both major and minor mergers. At least half of the cluster mergers are gas-poor, as indicated by their red colors and low 24 μm fluxes. Two of the double-nucleated cluster members have X-ray detected active galactic nuclei with L x > 10 43 erg s –1 , and are strong candidates for dual or offset super-massive black holes. We conclude that the massive z = 1.62 proto-cluster galaxies are undergoing accelerated assembly via minor mergers, and discuss the implications for galaxy evolution in proto-cluster environments

Binaries discovered by the SPY survey VI. Discovery of a low mass companion to the hot subluminous planetary nebula central star EGB5-a recently ejected common envelope?

OpenAIRE

Geier, S.; Napiwotzki, R.; Heber, U.; Nelemans, G.A.

2011-01-01

Hot subdwarf B stars (sdBs) in close binary systems are assumed to be formed via common envelope ejection. According to theoretical models, the amount of energy and angular momentum deposited in the common envelope scales with the mass of the companion. That low mass companions near or below the core hydrogen-burning limit are able to trigger the ejection of this envelope is well known. The currently known systems have very short periods $\\simeq0.1-0.3\\,{\\rm d}$. Here we report the discovery ...

FIRST INVESTIGATION OF THE COMBINED IMPACT OF IONIZING RADIATION AND MOMENTUM WINDS FROM A MASSIVE STAR ON A SELF-GRAVITATING CORE

International Nuclear Information System (INIS)

Ngoumou, Judith; Hubber, David; Dale, James E.; Burkert, Andreas

2015-01-01

Massive stars shape the surrounding interstellar matter (ISM) by emitting ionizing photons and ejecting material through stellar winds. To study the impact of the momentum from the wind of a massive star on the surrounding neutral or ionized material, we implemented a new HEALPix-based momentum-conserving wind scheme in the smoothed particle hydrodynamics (SPH) code SEREN. A qualitative study of the impact of the feedback from an O7.5-like star on a self-gravitating sphere shows that on its own, the transfer of momentum from a wind onto cold surrounding gas has both a compressing and dispersing effect. It mostly affects gas at low and intermediate densities. When combined with a stellar source's ionizing ultraviolet (UV) radiation, we find the momentum-driven wind to have little direct effect on the gas. We conclude that during a massive star's main sequence, the UV ionizing radiation is the main feedback mechanism shaping and compressing the cold gas. Overall, the wind's effects on the dense gas dynamics and on the triggering of star formation are very modest. The structures formed in the ionization-only simulation and in the combined feedback simulation are remarkably similar. However, in the combined feedback case, different SPH particles end up being compressed. This indicates that the microphysics of gas mixing differ between the two feedback simulations and that the winds can contribute to the localized redistribution and reshuffling of gas

Spitzer view of massive star formation in the tidally stripped Magellanic Bridge

International Nuclear Information System (INIS)

Chen, C.-H. Rosie; Indebetouw, Remy; Muller, Erik; Kawamura, Akiko; Gordon, Karl D.; Meixner, Margaret; Seale, Jonathan P.; Shiao, Bernie; Sewiło, Marta; Whitney, Barbara A.; Meade, Marilyn R.; Fukui, Yasuo; Madden, Suzanne C.; Oliveira, Joana M.; Van Loon, Jacco Th.; Robitaille, Thomas P.

2014-01-01

The Magellanic Bridge is the nearest low-metallicity, tidally stripped environment, offering a unique high-resolution view of physical conditions in merging and forming galaxies. In this paper, we present an analysis of candidate massive young stellar objects (YSOs), i.e., in situ, current massive star formation (MSF) in the Bridge using Spitzer mid-IR and complementary optical and near-IR photometry. While we definitely find YSOs in the Bridge, the most massive are ∼10 M ☉ , <<45 M ☉ found in the LMC. The intensity of MSF in the Bridge also appears to be decreasing, as the most massive YSOs are less massive than those formed in the past. To investigate environmental effects on MSF, we have compared properties of massive YSOs in the Bridge to those in the LMC. First, YSOs in the Bridge are apparently less embedded than in the LMC: 81% of Bridge YSOs show optical counterparts, compared to only 56% of LMC sources with the same range of mass, circumstellar dust mass, and line-of-sight extinction. Circumstellar envelopes are evidently more porous or clumpy in the Bridge's low-metallicity environment. Second, we have used whole samples of YSOs in the LMC and the Bridge to estimate the probability of finding YSOs at a given H I column density, N(H I). We found that the LMC has ∼3 × higher probability than the Bridge for N(H I) >12 × 10 20 cm –2 , but the trend reverses at lower N(H I). Investigating whether this lower efficiency relative to H I is due to less efficient molecular cloud formation or to less efficient cloud collapse, or to both, will require sensitive molecular gas observations.

Spitzer view of massive star formation in the tidally stripped Magellanic Bridge

Energy Technology Data Exchange (ETDEWEB)

Chen, C.-H. Rosie; Indebetouw, Remy [Department of Astronomy, University of Virginia, Charlottesville, VA 22904 (United States); Muller, Erik; Kawamura, Akiko [National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Gordon, Karl D.; Meixner, Margaret; Seale, Jonathan P.; Shiao, Bernie [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Sewiło, Marta [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States); Whitney, Barbara A.; Meade, Marilyn R. [Department of Astronomy, University of Wisconsin-Madison, Madison, WI 53706 (United States); Fukui, Yasuo [Department of Astrophysics, Nagoya University, Furocho, Chikusaku, Nagoya 464-8602 (Japan); Madden, Suzanne C. [CEA, Laboratoire AIM, Irfu/SAp, Orme des Merisiers, F-91191 Gif-sur-Yvette (France); Oliveira, Joana M.; Van Loon, Jacco Th. [Astrophysics Group, Lennard-Jones Laboratories, Keele University, Keele, Staffordshire ST5 5BG (United Kingdom); Robitaille, Thomas P., E-mail: rchen@mpifr-bonn.mpg.de [Max Planck Institute for Astronomy, D-69117 Heidelberg (Germany)

2014-04-20

The Magellanic Bridge is the nearest low-metallicity, tidally stripped environment, offering a unique high-resolution view of physical conditions in merging and forming galaxies. In this paper, we present an analysis of candidate massive young stellar objects (YSOs), i.e., in situ, current massive star formation (MSF) in the Bridge using Spitzer mid-IR and complementary optical and near-IR photometry. While we definitely find YSOs in the Bridge, the most massive are ∼10 M {sub ☉}, <<45 M {sub ☉} found in the LMC. The intensity of MSF in the Bridge also appears to be decreasing, as the most massive YSOs are less massive than those formed in the past. To investigate environmental effects on MSF, we have compared properties of massive YSOs in the Bridge to those in the LMC. First, YSOs in the Bridge are apparently less embedded than in the LMC: 81% of Bridge YSOs show optical counterparts, compared to only 56% of LMC sources with the same range of mass, circumstellar dust mass, and line-of-sight extinction. Circumstellar envelopes are evidently more porous or clumpy in the Bridge's low-metallicity environment. Second, we have used whole samples of YSOs in the LMC and the Bridge to estimate the probability of finding YSOs at a given H I column density, N(H I). We found that the LMC has ∼3 × higher probability than the Bridge for N(H I) >12 × 10{sup 20} cm{sup –2}, but the trend reverses at lower N(H I). Investigating whether this lower efficiency relative to H I is due to less efficient molecular cloud formation or to less efficient cloud collapse, or to both, will require sensitive molecular gas observations.

A THERMAL INFRARED IMAGING STUDY OF VERY LOW MASS, WIDE-SEPARATION BROWN DWARF COMPANIONS TO UPPER SCORPIUS STARS: CONSTRAINING CIRCUMSTELLAR ENVIRONMENTS

Energy Technology Data Exchange (ETDEWEB)

Bailey, Vanessa; Hinz, Philip M.; Su, Kate Y. L.; Hoffmann, William F.; Rieke, George; Rodigas, Timothy; Skemer, Andrew; Vaitheeswaran, Vidhya [Steward Observatory, University of Arizona, 933 N. Cherry Ave., Tucson, AZ 85721 (United States); Currie, Thayne [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4 (Canada); Esposito, Simone; Pinna, Enrico; Puglisi, Alfio [Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, I-50125 Firenze (Italy); Hill, John M. [Large Binocular Telescope Observatory, University of Arizona, 933 N. Cherry Ave., Tucson, AZ 85721 (United States); Jones, Terry [School of Physics and Astronomy, University of Minnesota, 116 Church St. SE, Minneapolis, MN 55455 (United States); Kim, Jihun [College of Optical Sciences, University of Arizona, 1630 E. University Blvd., Tucson, AZ 85721 (United States); Leisenring, Jarron; Meyer, Michael [Institut fuer Angewandte Physik, Eidgenoessische Technische Hochschule-Zuerich, CH-8093 (Switzerland); Murray-Clay, Ruth; Skrutskie, Michael F. [Harvard-Smithsonian Center for Astrophysics, Harvard University, 60 Garden St., Cambridge, MA 02138 (United States); Nelson, Matthew J., E-mail: vbailey@as.arizona.edu [Department of Astronomy, University of Virginia, Charlottesville, VA 22904 (United States); and others

2013-04-10

We present a 3-5 {mu}m LBT/MMT adaptive optics imaging study of three Upper Scorpius stars with brown dwarf (BD) companions with very low masses/mass ratios (M{sub BD} <25 M{sub Jup}; M{sub BD}/M{sub *} Almost-Equal-To 1%-2%) and wide separations (300-700 AU): GSC 06214, 1RXS 1609, and HIP 78530. We combine these new thermal IR data with existing 1-4 {mu}m and 24 {mu}m photometry to constrain the properties of the BDs and identify evidence for circumprimary/circumsecondary disks in these unusual systems. We confirm that GSC 06214B is surrounded by a disk, further showing that this disk produces a broadband IR excess due to small dust near the dust sublimation radius. An unresolved 24 {mu}m excess in the system may be explained by the contribution from this disk. 1RXS 1609B exhibits no 3-4 {mu}m excess, nor does its primary; however, the system as a whole has a modest 24 {mu}m excess, which may come from warm dust around the primary and/or BD. Neither object in the HIP 78530 system exhibits near- to mid-IR excesses. We additionally find that the 1-4 {mu}m colors of HIP 78530B match a spectral type of M3 {+-} 2, inconsistent with the M8 spectral type assigned based on its near-IR spectrum, indicating that it may be a low-mass star rather than a BD. We present new upper limits on additional low-mass companions in the system (<5 M{sub Jup} beyond 175 AU). Finally, we examine the utility of circumsecondary disks as probes of the formation histories of wide BD companions, finding that the presence of a disk may disfavor BD formation near the primary with subsequent outward scattering.

A solar-type star polluted by calcium-rich supernova ejecta inside the supernova remnant RCW 86

Science.gov (United States)

Gvaramadze, Vasilii V.; Langer, Norbert; Fossati, Luca; Bock, Douglas C.-J.; Castro, Norberto; Georgiev, Iskren Y.; Greiner, Jochen; Johnston, Simon; Rau, Arne; Tauris, Thomas M.

2017-06-01

When a massive star in a binary system explodes as a supernova, its companion star may be polluted with heavy elements from the supernova ejecta. Such pollution has been detected in a handful of post-supernova binaries 1 , but none of them is associated with a supernova remnant. We report the discovery of a binary G star strongly polluted with calcium and other elements at the position of the candidate neutron star [GV2003] N within the young galactic supernova remnant RCW 86. Our discovery suggests that the progenitor of the supernova that produced RCW 86 could have been a moving star, which exploded near the edge of its wind bubble and lost most of its initial mass because of common-envelope evolution shortly before core collapse, and that the supernova explosion might belong to the class of calcium-rich supernovae — faint and fast transients 2,3 , the origin of which is strongly debated 4-6 .

Presupernova evolution of massive stars

International Nuclear Information System (INIS)

Weaver, T.A.; Zimmerman, G.B.; Woosley, S.E.

1977-01-01

Population I stars of 15 M/sub mass/ and 25 M/sub mass/ have been evolved from the zero-age main sequence through iron core collapse utilizing a numerical model that incorporates both implicit hydrodynamics and a detailed treatment of nuclear reactions. The stars end their presupernova evolution as red supergiants with photospheric radii of 3.9 x 10 13 cm and 6.7 x 10 13 cm, respectively, and density structures similar to those invoked to explain Type II supernova light curves on a strictly hydrodynamic basis. Both stars are found to form substantially neutronized ''iron'' cores of 1.56 M/sub mass/ and 1.61 M/sub mass/, and central electron abundances of 0.427 and 0.439 moles/g, respectively, during hydrostatic silicon burning. Just prior to collapse, the abundances of the elements in the 25 M/sub mass/ star (excluding the neutronized iron core) have ratios strikingly close to their solar system values over the mass range from oxygen to calcium, while the 15 M/sub mass/ star is characterized by large enhancements of Ne, Mg, and Si. It is pointed out on nucleosynthetic grounds that the mass of the neutronized core must represent a lower limit to the mass of the neutron star or black hole remnant that stars in this mass range can normally produce

BINARY FORMATION MECHANISMS: CONSTRAINTS FROM THE COMPANION MASS RATIO DISTRIBUTION

International Nuclear Information System (INIS)

Reggiani, Maddalena M.; Meyer, Michael R.

2011-01-01

We present a statistical comparison of the mass ratio distribution of companions, as observed in different multiplicity surveys, to the most recent estimate of the single-object mass function. The main goal of our analysis is to test whether or not the observed companion mass ratio distribution (CMRD) as a function of primary star mass and star formation environment is consistent with having been drawn from the field star initial mass function (IMF). We consider samples of companions for M dwarfs, solar-type stars, and intermediate-mass stars, both in the field as well as clusters or associations, and compare them with populations of binaries generated by random pairing from the assumed IMF for a fixed primary mass. With regard to the field we can reject the hypothesis that the CMRD was drawn from the IMF for different primary mass ranges: the observed CMRDs show a larger number of equal-mass systems than predicted by the IMF. This is in agreement with fragmentation theories of binary formation. For the open clusters α Persei and the Pleiades we also reject the IMF random-pairing hypothesis. Concerning young star-forming regions, currently we can rule out a connection between the CMRD and the field IMF in Taurus but not in Chamaeleon I. Larger and different samples are needed to better constrain the result as a function of the environment. We also consider other companion mass functions and we compare them with observations. Moreover the CMRD both in the field and clusters or associations appears to be independent of separation in the range covered by the observations. Combining therefore the CMRDs of M (1-2400 AU) and G (28-1590 AU) primaries in the field and intermediate-mass primary binaries in Sco OB2 (29-1612 AU) for mass ratios, q = M 2 /M 1 , from 0.2 to 1, we find that the best chi-square fit follows a power law dN/dq∝q β , with β = -0.50 ± 0.29, consistent with previous results. Finally, we note that the Kolmogorov-Smirnov test gives a ∼1

MODULES FOR EXPERIMENTS IN STELLAR ASTROPHYSICS (MESA): PLANETS, OSCILLATIONS, ROTATION, AND MASSIVE STARS

International Nuclear Information System (INIS)

Paxton, Bill; Cantiello, Matteo; Bildsten, Lars; Arras, Phil; Brown, Edward F.; Dotter, Aaron; Mankovich, Christopher; Montgomery, M. H.; Stello, Dennis; Timmes, F. X.; Townsend, Richard

2013-01-01

We substantially update the capabilities of the open source software package Modules for Experiments in Stellar Astrophysics (MESA), and its one-dimensional stellar evolution module, MESA star. Improvements in MESA star's ability to model the evolution of giant planets now extends its applicability down to masses as low as one-tenth that of Jupiter. The dramatic improvement in asteroseismology enabled by the space-based Kepler and CoRoT missions motivates our full coupling of the ADIPLS adiabatic pulsation code with MESA star. This also motivates a numerical recasting of the Ledoux criterion that is more easily implemented when many nuclei are present at non-negligible abundances. This impacts the way in which MESA star calculates semi-convective and thermohaline mixing. We exhibit the evolution of 3-8 M ☉ stars through the end of core He burning, the onset of He thermal pulses, and arrival on the white dwarf cooling sequence. We implement diffusion of angular momentum and chemical abundances that enable calculations of rotating-star models, which we compare thoroughly with earlier work. We introduce a new treatment of radiation-dominated envelopes that allows the uninterrupted evolution of massive stars to core collapse. This enables the generation of new sets of supernovae, long gamma-ray burst, and pair-instability progenitor models. We substantially modify the way in which MESA star solves the fully coupled stellar structure and composition equations, and we show how this has improved the scaling of MESA's calculational speed on multi-core processors. Updates to the modules for equation of state, opacity, nuclear reaction rates, and atmospheric boundary conditions are also provided. We describe the MESA Software Development Kit that packages all the required components needed to form a unified, maintained, and well-validated build environment for MESA. We also highlight a few tools developed by the community for rapid visualization of MESA star results

Structure of massive star forming clumps from the Red MSX Source Survey

Science.gov (United States)

Figura, Charles C.; Urquhart, J. S.; Morgan, L.

2014-01-01

We present ammonia (1,1) and (2,2) emission maps of 61 high-mass star forming regions drawn from the Red MSX Source (RMS) Survey and observed with the Green Bank Telescope's K-Band Focal Plane Array. We use these observations to investigate the spatial distribution of the environmental conditions associated with this sample of embedded massive young stellar objects (MYSOs). Ammonia is an excellent high-density tracer of star-forming regions as its hyperfine structure allows relatively simple characterisation of the molecular environment. These maps are used to measure the column density, kinetic gas temperature distributions and velocity structure across these regions. We compare the distribution of these properties to that of the associated dust and mid-infrared emission traced by the ATLASGAL 870 micron emission maps and the Spitzer GLIMPSE IRAC images. We present a summary of these results and highlight some of more interesting finds.

Do All O Stars Form in Star Clusters?

Science.gov (United States)

Weidner, C.; Gvaramadze, V. V.; Kroupa, P.; Pflamm-Altenburg, J.

The question whether or not massive stars can form in isolation or only in star clusters is of great importance for the theory of (massive) star formation as well as for the stellar initial mass function of whole galaxies (IGIMF-theory). While a seemingly easy question it is rather difficult to answer. Several physical processes (e.g. star-loss due to stellar dynamics or gas expulsion) and observational limitations (e.g. dust obscuration of young clusters, resolution) pose severe challenges to answer this question. In this contribution we will present the current arguments in favour and against the idea that all O stars form in clusters.

Massive binary stars and self-enrichment of Massive binary stars and self-enrichment of

NARCIS (Netherlands)

Izzard, R.G.; de Mink, S.E.; Pols, O.R.; Langer, N.; Sana, H.; de Koter, A.

2013-01-01

Globular clusters contain many stars with surface abundance patterns indicating contributions from hydrogen burning products, as seen in the anti-correlated elemental abundances of e.g. sodium and oxygen, and magnesium and aluminium. Multiple generations of stars can explain this phenomenon, with

Binary pulsar PSR 1718-19 contains a stripped main-sequence turn-off star

International Nuclear Information System (INIS)

Zwitter, T.

1993-05-01

Lyne et al. (1993) have recently announced the discovery of a 1-second globular cluster pulsar, 1718-19, in a 6.2-hour binary system which is embedded in a cloud of material originating from the companion star. However the incident flux of the pulsar's radiation on the companion is too low to ablate it and a main sequence companion is too small to fill its Roche lobe. Here I argue that the companion is a stripped turn-off star of 0.2-0.4 solar masses (M sun ) and with approx. 0.1M sun helium core. It has approx. 1.8-times larger radius than a main sequence star of equal mass. Its position in the Hertzsprung-Russell diagram overlaps that of a ∼ 0.65M sun main-sequence star. The evolutionary state of the companion and the highly magnetized slowly rotating neutron star place the system on the verge of the low mass X-ray binary phase. (author). 19 refs, 2 figs

Radiative transfer modelling of W33A MM1: 3-D structure and dynamics of a complex massive star forming region

Science.gov (United States)

Izquierdo, Andrés F.; Galván-Madrid, Roberto; Maud, Luke T.; Hoare, Melvin G.; Johnston, Katharine G.; Keto, Eric R.; Zhang, Qizhou; de Wit, Willem-Jan

2018-05-01

We present a composite model and radiative transfer simulations of the massive star forming core W33A MM1. The model was tailored to reproduce the complex features observed with ALMA at ≈0.2 arcsec resolution in CH3CN and dust emission. The MM1 core is fragmented into six compact sources coexisting within ˜1000 au. In our models, three of these compact sources are better represented as disc-envelope systems around a central (proto)star, two as envelopes with a central object, and one as a pure envelope. The model of the most prominent object (Main) contains the most massive (proto)star (M⋆ ≈ 7 M⊙) and disc+envelope (Mgas ≈ 0.4 M⊙), and is the most luminous (LMain ˜ 104 L⊙). The model discs are small (a few hundred au) for all sources. The composite model shows that the elongated spiral-like feature converging to the MM1 core can be convincingly interpreted as a filamentary accretion flow that feeds the rising stellar system. The kinematics of this filament is reproduced by a parabolic trajectory with focus at the center of mass of the region. Radial collapse and fragmentation within this filament, as well as smaller filamentary flows between pairs of sources are proposed to exist. Our modelling supports an interpretation where what was once considered as a single massive star with a ˜103 au disc and envelope, is instead a forming stellar association which appears to be virialized and to form several low-mass stars per high-mass object.

Adaptive Optics Observations of Exoplanets, Brown Dwarfs, and Binary Stars

Science.gov (United States)

Hinkley, Sasha

2012-04-01

The current direct observations of brown dwarfs and exoplanets have been obtained using instruments not specifically designed for overcoming the large contrast ratio between the host star and any wide-separation faint companions. However, we are about to witness the birth of several new dedicated observing platforms specifically geared towards high contrast imaging of these objects. The Gemini Planet Imager, VLT-SPHERE, Subaru HiCIAO, and Project 1640 at the Palomar 5m telescope will return images of numerous exoplanets and brown dwarfs over hundreds of observing nights in the next five years. Along with diffraction-limited coronagraphs and high-order adaptive optics, these instruments also will return spectral and polarimetric information on any discovered targets, giving clues to their atmospheric compositions and characteristics. Such spectral characterization will be key to forming a detailed theory of comparative exoplanetary science which will be widely applicable to both exoplanets and brown dwarfs. Further, the prevalence of aperture masking interferometry in the field of high contrast imaging is also allowing observers to sense massive, young planets at solar system scales (~3-30 AU)- separations out of reach to conventional direct imaging techniques. Such observations can provide snapshots at the earliest phases of planet formation-information essential for constraining formation mechanisms as well as evolutionary models of planetary mass companions. As a demonstration of the power of this technique, I briefly review recent aperture masking observations of the HR 8799 system. Moreover, all of the aforementioned techniques are already extremely adept at detecting low-mass stellar companions to their target stars, and I present some recent highlights.