scholarly journals On the Gaia DR2 distances for Galactic luminous blue variables

2019 ◽  
Vol 488 (2) ◽  
pp. 1760-1778 ◽  
Author(s):  
Nathan Smith ◽  
Mojgan Aghakhanloo ◽  
Jeremiah W Murphy ◽  
Maria R Drout ◽  
Keivan G Stassun ◽  
...  
Keyword(s):  
Main Sequence ◽  
Mass Range ◽  
Instability Strip ◽  
Single Star ◽  
Circumstellar Material ◽  
Luminous Blue Variables ◽  
Binary Evolution ◽  
Lower Luminosity ◽  
Gaia Dr2 ◽  
Wide Swath

ABSTRACT We examine parallaxes and distances for Galactic luminous blue variables (LBVs) in the Gaia second data release (DR2). The sample includes 11 LBVs and 14 LBV candidates. For about half of the sample, DR2 distances are either similar to commonly adopted literature values, or the DR2 values have large uncertainties. For the rest, reliable DR2 distances differ significantly from values in the literature, and in most cases the Gaia DR2 distance is smaller. Two key results are that the S Doradus instability strip may not be as clearly defined as previously thought, and that there exists a population of LBVs at relatively low luminosities. LBVs seem to occupy a wide swath from the end of the main sequence at the blue edge to ∼8000 K at the red side, with a spread in luminosity reaching as low as log(L/L⊙) ≈ 4.5. The lower-luminosity group corresponds to effective single-star initial masses of 10–25 M⊙, and includes objects that have been considered as confirmed LBVs. We discuss implications for LBVs including (1) their instability and origin in binary evolution, (2) connections to some supernova (SN) impostors such as the class of SN 2008S-like objects, and (3) LBVs that may be progenitors of SNe with dense circumstellar material across a wide initial mass range. Although some of the Gaia DR2 distances for LBVs have large uncertainty, this represents the most direct and consistent set of Galactic LBV distance estimates available in the literature.

scholarly journals Origins of Type Ibn SNe 2006jc/2015G in interacting binaries and implications for pre-SN eruptions

2019 ◽  
Vol 491 (4) ◽  
pp. 6000-6019 ◽  
Author(s):  
Ning-Chen Sun ◽  
Jusytn R Maund ◽  
Ryosuke Hirai ◽  
Paul A Crowther ◽  
Philipp Podsiadlowski
Keyword(s):  
Main Sequence ◽  
Hubble Space Telescope ◽  
Optical Observations ◽  
Initial Mass ◽  
Binary Interaction ◽  
Lower Mass ◽  
Single Star ◽  
Circumstellar Material ◽  
Luminous Blue Variables ◽  
Star Evolution

ABSTRACT Type Ibn supernovae (SNe Ibn) are intriguing stellar explosions whose spectra exhibit narrow helium lines with little hydrogen. They trace the presence of circumstellar material (CSM) formed via pre-SN eruptions of their stripped-envelope progenitors. Early work has generally assumed that SNe Ibn come from massive Wolf–Rayet (WR) stars via single-star evolution. In this paper, we report ultraviolet (UV) and optical observations of two nearby Type Ibn SNe 2006jc and 2015G conducted with the Hubble Space Telescope (HST) at late times. A point source is detected at the position of SN 2006jc, and we confirm the conclusion of Maund et al. that it is the progenitor’s binary companion. Its position on the Hertzsprung–Russell (HR) diagram corresponds to a star that has evolved off the main sequence (MS); further analysis implies a low initial mass for the companion star (M2 ≤ 12.3$^{+2.3}_{-1.5}$ M⊙) and a secondary-to-primary initial mass ratio very close to unity (q = M2/M1 ∼ 1); the SN progenitor’s hydrogen envelope had been stripped through binary interaction. We do not detect the binary companion of SN 2015G. For both SNe, the surrounding stellar populations have relatively old ages and argue against any massive WR stars as their progenitors. These results suggest that SNe Ibn may have lower mass origins in interacting binaries. As a result, they also provide evidence that the giant eruptions commonly seen in massive luminous blue variables (LBVs) can also occur in much lower mass, stripped-envelope stars just before core collapse.

scholarly journals The isolation of luminous blue variables resembles aging B-type supergiants, not the most massive unevolved stars

2019 ◽  
Vol 489 (3) ◽  
pp. 4378-4388 ◽  
Author(s):  
Nathan Smith
Keyword(s):  
Large Magellanic Cloud ◽  
Relative Difference ◽  
Single Star ◽  
B Stars ◽  
Luminous Blue Variables ◽  
Distant Galaxies ◽  
Nearby Galaxies ◽  
Binary Evolution ◽  
Good Tracer ◽  
Bright Blue

ABSTRACT Luminous blue variables (LBVs) are suprisingly isolated from the massive O-type stars that are their putative progenitors in single-star evolution, implicating LBVs as binary evolution products. Aadland et al. found that LBVs are, however, only marginally more dispersed than a photometrically selected sample of bright blue stars (BBS) in the Large Magellanic Cloud (LMC), leading them to suggest that LBV environments may not exclude a single-star origin. In both comparisons, LBVs have the same median separation, confirming that any incompleteness in the O-star sample does not fabricate LBV isolation. Instead, the relative difference arises because the photometric BBS sample is far more dispersed than known O-type stars. Evidence suggests that the large BBS separation arises because it traces less massive (∼20 M⊙), aging blue supergiants. Although photometric criteria used by A19 aimed to select only the most massive unevolved stars, visual-wavelength colour selection cannot avoid contamination because O and early B stars have almost the same intrinsic colour. Spectral types confirm that the BBS sample contains many B supergiants. Moreover, the observed BBS separation distribution matches that of spectroscopically confirmed early B supergiants, not O-type stars, and matches predictions for a roughly 10 Myr population, not a 3–4 Myr population. A broader implication for ages of stellar populations is that bright blue stars are not a good tracer of the youngest massive O-type stars. Bright blue stars in nearby galaxies (and unresolved blue light in distant galaxies) generally trace evolved blue supergiants akin to SN 1987A’s progenitor.

scholarly journals The fates of massive stars: exploring uncertainties in stellar evolution with metisse

2020 ◽  
Vol 497 (4) ◽  
pp. 4549-4564
Author(s):  
Poojan Agrawal ◽  
Jarrod Hurley ◽  
Simon Stevenson ◽  
Dorottya Szécsi ◽  
Chris Flynn
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
Massive Stars ◽  
Mass Range ◽  
Radial Expansion ◽  
Single Star ◽  
New Approach ◽  
Star Evolution ◽  
Order Of Magnitude ◽  
The Impact

ABSTRACT In the era of advanced electromagnetic and gravitational wave detectors, it has become increasingly important to effectively combine and study the impact of stellar evolution on binaries and dynamical systems of stars. Systematic studies dedicated to exploring uncertain parameters in stellar evolution are required to account for the recent observations of the stellar populations. We present a new approach to the commonly used single-star evolution (sse) fitting formulae, one that is more adaptable: method of interpolation for single star evolution (metisse). It makes use of interpolation between sets of pre-computed stellar tracks to approximate evolution parameters for a population of stars. We have used metisse with detailed stellar tracks computed by the modules for experiments in stellar astrophysics (mesa), the bonn evolutionary code (bec), and the Cambridge stars code. metisse better reproduces stellar tracks computed using the stars code compared to sse, and is on average three times faster. Using stellar tracks computed with mesa and bec, we apply metisse to explore the differences in the remnant masses, the maximum radial expansion, and the main-sequence lifetime of massive stars. We find that different physical ingredients used in the evolution of stars, such as the treatment of radiation-dominated envelopes, can impact their evolutionary outcome. For stars in the mass range 9–100 M⊙, the predictions of remnant masses can vary by up to 20 M⊙, while the maximum radial expansion achieved by a star can differ by an order of magnitude between different stellar models.

scholarly journals Supernovae from yellow, blue supergiants: origin and consequences for stellar evolution

2015 ◽  
Vol 11 (A29B) ◽  
pp. 211-211
Author(s):  
G. Meynet ◽  
J. Groh ◽  
C. Georgy ◽  
H. Saio ◽  
R. Kudritzki
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
Mass Range ◽  
Close Binary ◽  
Close Binaries ◽  
Core Collapse ◽  
Rotational Surface ◽  
Internal Mixing ◽  
Binary Evolution ◽  
Small Scatter

AbstractA few core collapse supernovae progenitors have been found to be yellow or blue supergiants. Weshall discuss possible scenarios involving single and close binary evolution allowing to explain this kind of corecollapse supernova progenitors. According to stellar models for both single and close binaries, blue supergiants, at theend of their nuclear lifetimes and thus progenitors of core collapse supernovae, present very different characteristicsfor what concerns their surface compositions, rotational surface velocities and pulsational properties with respect toblue supergiants in their core helium burning phase. We discuss how the small observed scatter of the flux-weightedgravity-luminosity (FWGL) relation of blue supergiants constrains the evolution of massive stars after the Main-Sequence phase and the nature of the progenitors of supernovae in the mass range between 12 and 40 solarmasses. The present day observed surface abundances of blue supergiants, of their pulsational properties, as well asthe small scatter of the FWGL relation provide strong constraints on both internal mixing and mass loss in massivestars and therefore on the end point of their evolution.

scholarly journals Are sdAs helium core stars?

2017 ◽  
Vol 26 (1) ◽  
Author(s):  
Ingrid Pelisoli ◽  
S. O. Kepler ◽  
Detlev Koester
Keyword(s):  
Main Sequence ◽  
Galactic Disk ◽  
Physical Nature ◽  
Sloan Digital Sky Survey ◽  
Distance Modulus ◽  
Main Sequence Stars ◽  
Sky Survey ◽  
Balmer Lines ◽  
Low Mass ◽  
Binary Evolution

AbstractEvolved stars with a helium core can be formed by non-conservative mass exchange interaction with a companion or by strong mass loss. Their masses are smaller than 0.5 M⊙. In the database of the Sloan Digital Sky Survey (SDSS), there are several thousand stars which were classified by the pipeline as dwarf O, B and A stars. Considering the lifetimes of these classes on the main sequence, and their distance modulus at the SDSS bright saturation, if these were common main sequence stars, there would be a considerable population of young stars very far from the galactic disk. Their spectra are dominated by Balmer lines which suggest effective temperatures around 8 000-10 000 K. Several thousand have significant proper motions, indicative of distances smaller than 1 kpc. Many show surface gravity in intermediate values between main sequence and white dwarf, 4.75 < log g < 6.5, hence they have been called sdA stars. Their physical nature and evolutionary history remains a puzzle. We propose they are not H-core main sequence stars, but helium core stars and the outcomes of binary evolution. We report the discovery of two new extremely-low mass white dwarfs among the sdAs to support this statement.

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 Molecular Opacities in Cool Dwarf Stars

1994 ◽  
Vol 146 ◽  
pp. 61-70
Author(s):  
James Liebert
Keyword(s):  
Main Sequence ◽  
Galactic Disk ◽  
Small Radius ◽  
The Sun ◽  
M Dwarfs ◽  
Hydrogen Burning ◽  
Dwarf Stars ◽  
Low Mass ◽  
High Space ◽  
Lower Luminosity

The term dwarf stars identifies objects of small radius in the Hertzsprung-Russell (H-R) Diagram, but encompasses more than one phase of stellar evolution. The M dwarfs (type dM) populate the main sequence at the low mass end; these are the coolest core hydrogen-burning stars. They belong generally to the Galactic disk, or Population I, have relatively small space motions with respect to the Sun, and have similar metallicities to the Sun (although perhaps only within a factor of several). In particular, this means that the abundance of oxygen is always greater than that of carbon. The M subdwarfs (sdM) are the Population II counterparts, showing low metallicities and high space motions. Because they have smaller radii, they define a main sequence at lower luminosity than the M dwarfs for a given temperature. Hence the term subdwarf.

scholarly journals Pulsations of Ob-Stars: New Observations

1998 ◽  
Vol 185 ◽  
pp. 347-354 ◽  
Author(s):  
Dietrich Baade
Keyword(s):  
Main Sequence ◽  
Physical Parameters ◽  
Be Stars ◽  
Instability Strip ◽  
Ob Stars ◽  
Analysis Strategies ◽  
The Galaxy ◽  
Order Line ◽  
Nonradial Pulsation ◽  
Radial Pulsations

Improved observing and data analysis strategies have initiated a considerable expansion of the empirical knowledge about the pulsations of OB stars. Possible correlations between physical parameters and associated pulsation characteristics are becoming more clearly perceivable. This starts to include the asteroseismologically fundamental areas of g-modes and rapid rotation. The β Cephei instability strip continues to be the only locus where radial pulsations occur (but apparently not in all stars located in that strip). Except for spectral types B8/B9 near the main sequence, where pulsations are hardly detected even at low amplitudes, any major group of stars in the Galaxy that are obviously not candidate pulsators still remains to be identified. However, the incidence and amplitudes of OB star pulsations decrease steeply with metallicity. The behaviour of high-luminosity stars is less often dominated by very few modes. In broad-lined stars the moving-bump phenomenon is more common than low-order line-profile variability. But its relation to nonradial pulsation is not clear. The beating of low-ℓ nonradial pulsation modes that have identical angular mode indices may be the clockwork of the outbursts of at least some Be stars. The physics of this episodic mass loss process remains to be identified.

scholarly journals Which stars can see Earth as a transiting exoplanet?

2020 ◽  
Vol 499 (1) ◽  
pp. L111-L115
Author(s):  
L Kaltenegger ◽  
J Pepper
Keyword(s):  
Main Sequence ◽  
Line Of Sight ◽  
Main Sequence Stars ◽  
Target List ◽  
Distant Observer ◽  
Spectroscopic Observations ◽  
Transiting Planets ◽  
Vantage Points ◽  
Life On Earth ◽  
Gaia Dr2

ABSTRACT Transit observations have found the majority of exoplanets to date. Also spectroscopic observations of transits and eclipses are the most commonly used tool to characterize exoplanet atmospheres and will be used in the search for life. However, an exoplanet’s orbit must be aligned with our line of sight to observe a transit. Here, we ask, from which stellar vantage points would a distant observer be able to search for life on Earth in the same way? We use the TESS Input Catalog and data from Gaia DR2 to identify the closest stars that could see Earth as a transiting exoplanet: We identify 1004 main-sequence stars within 100 parsecs, of which 508 guarantee a minimum 10-h long observation of Earth’s transit. Our star list consists of about 77 percent M-type, 12 percent K-type, 6 percent G-type, 4 percent F-type stars, and 1 percent A-type stars close to the ecliptic. SETI searches like the Breakthrough Listen Initiative are already focusing on this part of the sky. Our catalogue now provides a target list for this search. As part of the extended mission, NASA’s TESS will also search for transiting planets in the ecliptic to find planets that could already have found life on our transiting Earth .

scholarly journals The Origin of the RS CVn Binaries

1976 ◽  
Vol 73 ◽  
pp. 381-387 ◽  
Author(s):  
P. Biermann ◽  
D. S. Hall
Keyword(s):  
Angular Momentum ◽  
Star Formation ◽  
Total Mass ◽  
Total Angular Momentum ◽  
Main Sequence ◽  
Be Stars ◽  
Large Space ◽  
Single Star ◽  
The Core ◽  
Thermal Phase

We consider six possible origins for the RS CVn binaries based on the following possibilities. RS CVn binaries might now be either pre-main-sequence or post-main-sequence. A pre-main-sequence binary might not always have been a binary but might have resulted from fission of a rapidly rotating single pre-main-sequence star. The main-sequence counterparts might be either single stars or binaries.To decide which of the six origins is possible, we consider the following observed data for the RS CVn binaries: total mass, total angular momentum, lack of observed connection with regions of star formation, large space density, kinematical age, and the visual companion of WW Dra. In addition we consider lifetimes and space densities of single stars and other types of binaries.The only origin possible is that the RS CVn binaries are in a thermal phase following fission of a main-sequence single star. In this explanation the single star had a rapidly rotating core which became unstable due to the core contraction which made it begin to evolve off the main sequence. The present Be stars might be examples of such parent single stars.

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