scholarly journals Carina High-contrast Imaging Project for massive Stars (CHIPS)

2020 ◽  
Vol 640 ◽  
pp. A15
Author(s):  
A. Rainot ◽  
M. Reggiani ◽  
H. Sana ◽  
J. Bodensteiner ◽  
C. A. Gomez-Gonzalez ◽  
...  
Keyword(s):  
Main Sequence ◽  
Massive Stars ◽  
Imaging Techniques ◽  
Mass Function ◽  
Local Source ◽  
High Contrast ◽  
Contrast Imaging ◽  
Solar Mass ◽  
Low Mass ◽  
Spectral Channels

Context. Massive stars like company. However, low-mass companions have remained extremely difficult to detect at angular separations (ρ) smaller than 1″ (approx. 1000–3000 au, considering the typical distance to nearby massive stars) given the large brightness contrast between the companion and the central star. Constraints on the low-mass end of the companions mass-function for massive stars are needed, however, for helping, for example, to distinguish among the various scenarios that describe the formation of massive stars. Aims. With the aim of obtaining a statistically significant constraint on the presence of low-mass companions beyond the typical detection limit of current surveys (Δmag ≲ 5 at ρ ≲ 1″), we initiated a survey of O and Wolf-Rayet stars in the Carina region using the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) coronagraphic instrument on the Very Large Telescope (VLT). In this, the first paper of the series, we aim to introduce the survey, to present the methodology and to demonstrate the capability of SPHERE for massive stars using the multiple system QZ Car. Methods. We obtained VLT-SPHERE snapshot observations in the IRDIFS_EXT mode, which combines the IFS and IRDIS sub-systems and simultaneously provides us four-dimensional (4D) data cubes in two different fields-of-view: 1.73″ × 1.73″ for IFS (39 spectral channels across the YJH bands) and 12″ × 12″ for IRDIS (two spectral channels across the K band). Angular- and spectral-differential imaging techniques as well as PSF-fitting were applied to detect and measure the relative flux of the companions in each spectral channel. The latter were then flux-calibrated using theoretical SED models of the central object and compared to a grid of ATLAS9 atmosphere model and (pre-)main-sequence evolutionary tracks, providing a first estimate of the physical properties of the detected companions. Results. Detection limits of 9 mag at ρ >  200 mas for IFS, and as faint as 13 mag at ρ > 1.​″8 for IRDIS (corresponding to sub-solar masses for potential companions), can be reached in snapshot observations of only a few minutes integration times, allowing us to detect 19 sources around the QZ Car system. All but two are reported here for the first time. With near-IR magnitude contrasts in the range of 4 to 7.5 mag, the three brightest sources (Ab, Ad, and E) are most likely to be physically bound. They have masses in the range of 2 to 12 M⊙ and are potentially co-eval with QZ Car central system. The remaining sources have flux contrast of 1.5 × 105 to 9.5 × 106 (ΔK ≈ 11 to 13 mag). Their presence can be explained by the local source density and they are, thus, likely to be chance alignments. If they were members of the Carina nebula, they would be sub-solar-mass pre-main sequence stars. Conclusions. Based on this proof of concept, we show that the VLT/SPHERE allows us to reach the sub-solar mass regime of the companion mass function. It paves the way for this type of observation with a large sample of massive stars to provide novel constraints on the multiplicity of massive stars in a region of the parameter space that has remained inaccessible so far.

The Murky Depths of the Main Sequence: Nearby Speckled Dwarfs and Elusive Brown Beasts

1992 ◽  
Vol 135 ◽  
pp. 10-20
Author(s):  
Todd J. Henry ◽  
Donald W. McCarthy
Keyword(s):  
Main Sequence ◽  
Current Knowledge ◽  
Imaging Techniques ◽  
Mass Function ◽  
M Dwarfs ◽  
Red Dwarfs ◽  
Comprehensive Survey ◽  
Low Mass ◽  
M Dwarf

AbstractUsing infrared speckle imaging techniques, we have completed a comprehensive survey of all northern (δ ≥ −25°) M dwarfs within 8 parsecs for low mass companions. Of the 74 targets searched, six new companions were found. Included in the final census are four objects orbiting their primaries at sub-arcsecond separations which have masses near 80 Jupiters, making them viable brown dwarf candidates. Three of these — LHS 1047B, GL 623B and G 208-44B — are the faintest red objects for which masses have been determined and represent the limit of our current knowledge about the faint end of the mass-luminosity relation.The complete sample includes 99 members, and under further analysis reveals fundamental facts about the red dwarf population that were unknown until the present study: 1) 30-40 % of M dwarf primaries have companions, 2) more companions are found orbiting 1-10 AU from the primary than in any other decade interval, and 3) there are 50% fewer red dwarfs known in the more distant half of the survey volume, presumably because the parallax and proper motion surveys are incomplete.In addition, we find that the infrared luminosity function (LF) is fiat or rising toward the end of the main sequence, while the visible LF may be flat, and we illustrate that the determination of an accurate LF is critically sensitive to the resolution of binaries. A better description of the stellar population, the mass function, is found to be undoubtedly rising to the stellar/substellar break. Finally, we have developed a much-needed mass-luminosity relation for stars of mass 1.2 to 0.08 M⊙, and using these relations find that the M dwarfs contribute ~0.2 M⊙/pc3 to the galactic mass.

scholarly journals Rotational Evolution of Intermediate and Low Mass Main Sequence Stars

2004 ◽  
Vol 215 ◽  
pp. 127-135
Author(s):  
John R. Stauffer
Keyword(s):  
Main Sequence ◽  
Massive Stars ◽  
Rotational Velocity ◽  
Open Cluster ◽  
Open Clusters ◽  
Solar Mass ◽  
Low Mass Stars ◽  
Cluster Data ◽  
Rotational Evolution ◽  
Low Mass

Bob Kraft (1967) showed that there is a break in the mean rotational velocity of stars at about spectral type F5, with more massive stars generally being rapid rotators and less massive stars generally being slow rotators. He also showed that in the late F spectral range at least, there is an evolution with time on the main sequence, with younger F stars being more rapidly rotating. Kraft's observational database extended only to about one solar mass due to the sensitivy limitations of photographic plates. Modern observations of low mass stars in open clusters, extending down in mass to nearly the hydrogen burning mass limit in a few clusters, have since been used to show that rotational spindown is the common feature of stars less massive than the sun but that there is a wide spread in rotational velocities when stars arrive on the ZAMS. I will review what is known empirically concerning the rotational velocities of intermediate and low mass field stars, using the open cluster data to place the field star observations in context.

scholarly journals Adaptive Optics Observations of Exoplanets, Brown Dwarfs, and Binary Stars

2011 ◽  
Vol 7 (S282) ◽  
pp. 181-188
Author(s):  
Sasha Hinkley
Keyword(s):  
Adaptive Optics ◽  
Binary Stars ◽  
Imaging Techniques ◽  
Contrast Ratio ◽  
Brown Dwarfs ◽  
Formation Mechanisms ◽  
High Contrast ◽  
Contrast Imaging ◽  
High Contrast Imaging ◽  
Low Mass

AbstractThe 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.

scholarly journals The VLT-FLAMES Tarantula Survey

2016 ◽  
Vol 12 (S329) ◽  
pp. 279-286
Author(s):  
Jorick S. Vink ◽  
C.J. Evans ◽  
J. Bestenlehner ◽  
C. McEvoy ◽  
O. Ramírez-Agudelo ◽  
...  
Keyword(s):  
Mass Loss ◽  
Main Sequence ◽  
Massive Stars ◽  
Mass Function ◽  
Large Magellanic Cloud ◽  
Initial Mass Function ◽  
Data Set ◽  
Large Program ◽  
Medium Resolution ◽  
Key Questions

AbstractWe present a number of notable results from the VLT-FLAMES Tarantula Survey (VFTS), an ESO Large Program during which we obtained multi-epoch medium-resolution optical spectroscopy of a very large sample of over 800 massive stars in the 30 Doradus region of the Large Magellanic Cloud (LMC). This unprecedented data-set has enabled us to address some key questions regarding atmospheres and winds, as well as the evolution of (very) massive stars. Here we focus on O-type runaways, the width of the main sequence, and the mass-loss rates for (very) massive stars. We also provide indications for the presence of a top-heavy initial mass function (IMF) in 30 Dor.

scholarly journals Stellar models and isochrones from low-mass to massive stars including pre-main sequence phase with accretion

2019 ◽  
Vol 624 ◽  
pp. A137 ◽  
Author(s):  
L. Haemmerlé ◽  
P. Eggenberger ◽  
S. Ekström ◽  
C. Georgy ◽  
G. Meynet ◽  
...  
Keyword(s):  
Star Formation ◽  
Stellar Evolution ◽  
Main Sequence ◽  
Massive Stars ◽  
Mass Range ◽  
Stellar Clusters ◽  
Solar Metallicity ◽  
Low Mass ◽  
Stellar Models ◽  
Young Clusters

Grids of stellar models are useful tools to derive the properties of stellar clusters, in particular young clusters hosting massive stars, and to provide information on the star formation process in various mass ranges. Because of their short evolutionary timescale, massive stars end their life while their low-mass siblings are still on the pre-main sequence (pre-MS) phase. Thus the study of young clusters requires consistent consideration of all the phases of stellar evolution. But despite the large number of grids that are available in the literature, a grid accounting for the evolution from the pre-MS accretion phase to the post-MS phase in the whole stellar mass range is still lacking. We build a grid of stellar models at solar metallicity with masses from 0.8 M⊙ to 120 M⊙, including pre-MS phase with accretion. We use the GENEC code to run stellar models on this mass range. The accretion law is chosen to match the observations of pre-MS objects on the Hertzsprung-Russell diagram. We describe the evolutionary tracks and isochrones of our models. The grid is connected to previous MS and post-MS grids computed with the same numerical method and physical assumptions, which provides the widest grid in mass and age to date.

scholarly journals The Stellar Initial Mass Function in Starburst Galaxies

1999 ◽  
Vol 186 ◽  
pp. 243-250
Author(s):  
Claus Leitherer
Keyword(s):  
Massive Stars ◽  
Mass Function ◽  
Starburst Galaxies ◽  
Initial Mass Function ◽  
Initial Mass ◽  
H Ii Regions ◽  
Environmental Properties ◽  
Stellar Initial Mass Function ◽  
Low Mass ◽  
Star Formation Histories

Starburst galaxies are currently forming massive stars at prodigious rates. I discuss the star-formation histories and the shape of the initial mass function, with particular emphasis on the high- and on the low-mass end. The classical Salpeter IMF is consistent with constraints from observations of the most massive stars, irrespective of environmental properties. The situation at the low-mass end is less clear: direct star counts in nearby giant H II regions show stars down to ~1 M⊙, whereas dynamical arguments in some starburst galaxies suggest a deficit of such stars.

scholarly journals Supernova Nucleosynthesis in Massive Stars

1996 ◽  
Vol 145 ◽  
pp. 157-164
Author(s):  
M. Hashimoto ◽  
K. Nomoto ◽  
T. Tsujimoto ◽  
F.-K. Thielemann
Keyword(s):  
Main Sequence ◽  
Massive Stars ◽  
Mass Function ◽  
Stellar Mass ◽  
Initial Mass Function ◽  
Explosion Energy ◽  
Initial Mass ◽  
Explosive Nucleosynthesis ◽  
Solar Abundances

Presupernova evolution and explosive nucleosynthesis in massive stars for main-sequence masses from 13 Mʘ to 70 Mʘ are calculated. We examine the dependence of the supernova yields on the stellar mass, 12C(α, γ)16O rate, and explosion energy. The supernova yields integrated over the initial mass function are compared with the solar abundances.

scholarly journals Age-related observations of low mass pre-main and young main sequence stars

2008 ◽  
Vol 4 (S258) ◽  
pp. 81-94 ◽  
Author(s):  
Lynne A. Hillenbrand
Keyword(s):  
Main Sequence ◽  
Rotation Period ◽  
Age Dating ◽  
Main Sequence Stars ◽  
Solar Mass ◽  
Age Related ◽  
Stellar Ages ◽  
Dating Methods ◽  
Low Mass ◽  
Lithium Depletion

AbstractThis overview summarizes the age dating methods available for young sub-solar mass stars. Pre-main sequence age diagnostics include the Hertzsprung-Russell (HR) diagram, spectroscopic surface gravity indicators, and lithium depletion; asteroseismology is also showing recent promise. Near and beyond the zero-age main sequence, rotation period or vsiniand activity (coronal and chromospheric) diagnostics along with lithium depletion serve as age proxies. Other authors in this volume present more detail in each of the aforementioned areas. Herein, I focus on pre-main sequence HR diagrams and address the questions: Do empirical young cluster isochrones match theoretical isochrones? Do isochrones predict stellar ages consistent with those derived via other independent techniques? Do the observed apparent luminosity spreads at constant effective temperature correspond to true age spreads? While definitive answers to these questions are not provided, some methods of progression are outlined.

scholarly journals Discovery of Three Very Low Mass Binary Systems: An Adaptive Optics Survey of M6.0–M7.5 Stars

2003 ◽  
Vol 211 ◽  
pp. 257-260
Author(s):  
Nick Siegler ◽  
Laird M. Close ◽  
Eric E. Mamajek ◽  
Melanie Freed
Keyword(s):  
Adaptive Optics ◽  
Binary Systems ◽  
Main Sequence ◽  
Main Sequence Stars ◽  
Solar Mass ◽  
Low Mass ◽  
M Stars ◽  
Adaptive Optics System

We have used the adaptive optics system Hōkūpa'a at Gemini North to search for companions from a flux-limited (Ks > 12) survey of 30 nearby M6.0–M7.5 dwarfs. Our observations, which are sensitive to companions with separations > 0.1″ (~ 2.8 AU), detect 3 new binary systems. This implies an overall binary fraction of 9±4% for M6.0–M7.5 binaries. This binary frequency is somewhat less than the 19±7% measured for late M stars and ~ 20% for L stars, but is still statistically consistent. However, the result is significantly lower than the binary fractions observed amongst solar mass main sequence stars (~60%) and early M stars (~35%).

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