Photometric surveys at optical, ultraviolet, and infrared wavelengths provide ever-growing datasets as major surveys proceed. Colour-colour diagrams are useful tools to identify classes of star and ...provide large samples. However, combining all photometric measurements of a star into a spectral energy distribution will allow quantitative analyses to be carried out. We demonstrate how to construct and exploit spectral energy distributions and colours for sublumious B (sdB) stars. The aim is to identify cool companions to hot subdwarfs and to determine atmospheric parameters of apparently single sdB stars as well as composite spectrum sdB binaries.We analyse two sdB stars with high-quality photometric data which serve as our benchmarks, the apparently single sdB HD205805 and the sdB + K5 binary PG 0749+658, briefly present preliminary results for the sample of 142 sdB binaries with known orbits, and discuss future prospects from ongoing all-sky optical space- (Gaia) and ground-based (e.g. SkyMapper) as well as NIR surveys.
Spectroscopy of hot subdwarf binaries Kreuzer, Simon; Irrgang, Andreas; Heber, Ulrich
Open Astronomy,
06/2018, Letnik:
27, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We present a status report of our spectroscopic analysis of subdwarf binaries consisting of a subdwarf and a F/G/K-type main-sequence companion. These systems selected from SDSS photometry show ...significant excess in the (infra-)red which can not be explained by interstellar reddening. Inspection of SDSS spectra revealed that most of them are composite spectrum sdB binaries. Once their spectra are disentangled, a detailed spectral analysis can be carried out. It reveals T
, log g and the metal abundance of each individual star. The cool companion is of particular interest, because its spectrum reveals the original chemical composition of the binary.
The evolved slowly pulsating B star 18 Peg Irrgang, Andreas; De Cat, Peter; Tkachenko, Andrew
EPJ Web of Conferences,
01/2017, Letnik:
152
Conference Proceeding, Journal Article
Recenzirano
Odprti dostop
The predicted width of the upper main sequence in stellar evolution models depends on the empirical calibration of the convective overshooting parameter. Despite decades of discussions, its precise ...value is still unknown and further observational constraints are required to gauge it. Irrgang et al. (1) showed that the B3 III giant 18 Peg is one of the most evolved members of the class of slowly pulsating B (SPB) stars and, thus, bears tremendous potential to derive a tight lower limit for the width of the upper main sequence. In addition, 18 Peg turns out to be part of a single-lined spectroscopic binary system with an eccentric, more than 6-year orbit. The orbital solution, in combination with the absence of additional signatures of the secondary component in the spectroscopic data and the spectral energy distribution, lead to the conclusion that all the observations of 18 Peg are fully compatible with the assumption that the secondary component is either a main-sequence star with a mass of 1-4 M⊙ or a neutron star.
Since the discovery of hypervelocity stars in 2005, it has been widely believed that only the disruption of a binary system by a supermassive black hole at the Galactic center (GC), that is, the ...so-called Hills mechanism, is capable of accelerating stars to beyond the Galactic escape velocity. In the meantime, however, driven by the
Gaia
space mission, there is mounting evidence that many of the most extreme high-velocity early-type stars at high Galactic latitudes do originate in the Galactic disk and not in the GC. Moreover, the ejection velocities of these extreme disk-runaway stars exceed the predicted limits of the classical scenarios for the production of runaway stars. Based on proper motions from the
Gaia
early data release 3 and on recent and new spectrophotometric distances, we studied the kinematics of 30 such extreme disk-runaway stars, allowing us to deduce their spatial origins in and their ejection velocities from the Galactic disk with unprecedented precision. Only three stars in the sample have past trajectories that are consistent with an origin in the GC, most notably S5-HVS 1, which is the most extreme object in the sample by far. All other program stars are shown to be disk runaways with ejection velocities that sharply contrast at least with classical ejection scenarios. They include HVS 5 and HVS 6, which are both gravitationally unbound to the Milky Way. While most stars originate from within a galactocentric radius of 15 kpc, which corresponds to the observed extent of the spiral arms, a group of five stars stems from radii of about 21−29 kpc. This indicates a possible link to outer Galactic rings and a potential origin from infalling satellite galaxies.
Context.
The ESA
Gaia
mission is a remarkable tool for stellar population analysis through its accurate Hertzsprung–Russell diagram. Its precise astrometry has propelled detailed kinematic studies of ...the Milky Way and the identification of high-velocity outliers.
Aims.
Motivated by the historical identification of runaway main-sequence (MS) stars of an early spectral type at high Galactic latitudes, we test the capability of
Gaia
at identifying new such stars.
Methods.
We selected ≈2300 sources with
Gaia
magnitudes of
G
BP
−
G
RP
≤ 0.05, which are compatible with the colors of low-extinction MS stars that are earlier than a mid-A spectral type, and obtained low-resolution optical spectroscopy for 48 such stars. By performing detailed photometric and spectroscopic analyses, we derived their atmospheric and physical parameters (effective temperature, surface gravity, radial velocity, interstellar reddening, spectrophotometric distance, mass, radius, luminosity, and age). The comparison between spectrophotometric and parallax-based distances enabled us to disentangle the MS candidates from older blue horizontal branch (BHB) candidates.
Results.
We identify 12 runaway MS candidates, with masses between 2 and 6
M
⊙
. Their trajectories were traced back to the Galactic disk in order to identify their most recent Galactic plane crossings and the corresponding flight times. All 12 candidates are ejected from the Galactic disk within 2 to 16.5 kpc from the Galactic center and possess flight times that are shorter than their evolutionary ages, which is compatible with a runaway hypothesis. Three MS candidates have ejection velocities exceeding 450 km s
−1
, thus, they appear to challenge the canonical ejection scenarios for late B-type stars. The fastest star of our sample also has a non-negligible Galactic escape probability if its MS nature can be confirmed. We identify 27 BHB candidates, and the two hottest stars in our sample are rare low-mass stars of late O- and early B-types, evolving towards the white dwarf cooling sequence.
Conclusions.
The combination of
Gaia
parallaxes and proper motions can lead to the efficient selection of runaway blue MS candidates up to 10 kpc away from the Sun. High resolution spectra are needed to confirm the MS status, via precise measurements of projected rotational velocities and chemical compositions.
Decades ago,
He isotope enrichment in helium-weak B-type main-sequence, in blue horizontal branch and in hot subdwarf B (sdB) stars, i.e., helium-core burning stars of the extreme horizontal branch, ...were discovered. Diffusion processes in the atmosphere of these stars lead to the observed abundance anomalies. Quantitative spectral analyses of high-resolution spectra to derive photospheric isotopic helium abundance ratios for known
He sdBs have not been performed yet. We present preliminary results of high-resolution and high S/N spectra to determine the
He and
He abundances of nine known
He sdBs. We used a hybrid local/non-local thermodynamic equilibrium (LTE/NLTE) approach for B-type stars investigating multiple He i lines, including λ4922 Å and λ6678 Å, which show the strongest isotopic shifts in the optical spectral range.We also report the discovery of four new 3He sdBs from the ESO Supernova Progenitor survey. Most of the
He sdBs cluster in a narrow temperature strip between ∼ 26000 K and ∼ 30000 K and have almost no atmospheric
He at all. Interestingly, three
He sdBs show evidence for vertical helium stratification.
HW Vir systems are rare eclipsing binary systems including a subdwarf B star (sdB) with a faint companion, mostly M-dwarfs. Up to now, 19 HW Vir systems have been published, three of them with ...substellar companions. We report the spectroscopic as well as photometric observation of the eclipsing sdB binary PTF1 J011339.09+225739.1 (PTF1 J0113) in a close (a=0.722 ± 0.023 R⊙), short period (P = 0.0933731(3)d) orbit. A quantitative spectral analysis of the sdB yields Te.=29280 ± 720 K, log(g)=5.77 ± 0.09 dex, and log(y)=−2.32 ± 0.12. The circular orbital velocity of the sdB of K1=74.2 ± 1.7 km s−1 is derived from the radial velocity curve. Except for the strong reflection effect, no other light contribution of the companion could be detected. The light curves - recorded with ULTRACAM - were analyzed using the Wilson-Devinney code. We find an inclination angle of i=79.88 ± 0.18∘. Because our first attempts to determine q failed, we calculated large grids of synthetic lightcurves for several mass ratios. Because of degeneracy, good solutions for different mass ratios were found - the one at q = 0.24 is consistent with the sdB’s canonical mass (MsdB = 0.47 M⊙). Accordingly, the mass of the companion is M2=0.112 ± 0.003 M⊙. The radii of the two components were also derived: RsdB=0.178 ± 0.006 R⊙ and R2 = 0.158 ± 0.009 R⊙. Thus, the results for the secondary are consistent with an M-dwarf as secondary
Context. The ESA Gaia mission is a remarkable tool for stellar population analysis through its accurate Hertzsprung–Russell diagram. Its precise astrometry has propelled detailed kinematic studies of ...the Milky Way and the identification of high-velocity outliers. Aims. Motivated by the historical identification of runaway main-sequence (MS) stars of an early spectral type at high Galactic latitudes, we test the capability of Gaia at identifying new such stars. Methods. We selected ≈2300 sources with Gaia magnitudes of GBP − GRP ≤ 0.05, which are compatible with the colors of low-extinction MS stars that are earlier than a mid-A spectral type, and obtained low-resolution optical spectroscopy for 48 such stars. By performing detailed photometric and spectroscopic analyses, we derived their atmospheric and physical parameters (effective temperature, surface gravity, radial velocity, interstellar reddening, spectrophotometric distance, mass, radius, luminosity, and age). The comparison between spectrophotometric and parallax-based distances enabled us to disentangle the MS candidates from older blue horizontal branch (BHB) candidates. Results. We identify 12 runaway MS candidates, with masses between 2 and 6 M⊙. Their trajectories were traced back to the Galactic disk in order to identify their most recent Galactic plane crossings and the corresponding flight times. All 12 candidates are ejected from the Galactic disk within 2 to 16.5 kpc from the Galactic center and possess flight times that are shorter than their evolutionary ages, which is compatible with a runaway hypothesis. Three MS candidates have ejection velocities exceeding 450 km s−1, thus, they appear to challenge the canonical ejection scenarios for late B-type stars. The fastest star of our sample also has a non-negligible Galactic escape probability if its MS nature can be confirmed. We identify 27 BHB candidates, and the two hottest stars in our sample are rare low-mass stars of late O- and early B-types, evolving towards the white dwarf cooling sequence. Conclusions. The combination of Gaia parallaxes and proper motions can lead to the efficient selection of runaway blue MS candidates up to 10 kpc away from the Sun. High resolution spectra are needed to confirm the MS status, via precise measurements of projected rotational velocities and chemical compositions.
Using ESO FEROS archive spectra of several southern OB-type binaries, we derived periods for three SB2 spectroscopic binaries, HD 97166, HD 115455, and HD 123590, and two SB1 systems, HD 130298 and ...HD 163892. It was also possible to use new FEROS spectra to improve the parameters of the known binaries, KX Vel and HD 167263. For KX Vel, we determined a dynamic mass of the primary of 16.8 M⊙, while the evolutionary model suggests a higher value of 20.2 M⊙. We derived an improved period for HD 167263, and in its spectra, we recognized contributions of both of its interferometric components.
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