scholarly journals SALT revisits DY Cen: a rapidly evolving strontium-rich single helium star

2020 ◽  
Vol 493 (3) ◽  
pp. 3565-3579 ◽  
Author(s):  
C Simon Jeffery ◽  
N Kameswara Rao ◽  
David L Lambert
Keyword(s):  
High Surface ◽  
Rapid Evolution ◽  
High Resolution Spectroscopy ◽  
Pulsation Period ◽  
Surface Hydrogen ◽  
Type Variable ◽  
Binary Orbit ◽  
R Crb Type ◽  
Helium Star ◽  
Process Element

ABSTRACT The hydrogen-deficient star DY Cen has been reported as an R CrB-type variable, an extreme helium star (with some hydrogen), and as a single-lined spectroscopic binary. It has been associated with a dramatic change in visual brightness and colour corresponding to a change in effective temperature ( Teff) of some 20 000 K in the last century. To characterize the binary orbit and  Teff changes more precisely, new high-resolution spectroscopy has been obtained with SALT. The previous orbital period is not confirmed; previous measurements may have been confused by the presence of pulsations. Including data from earlier epochs (1987, 2002, and 2010), self-consistent spectral analyses from all four epochs demonstrate an increase in  Teff from 18 800 to 24 400 K between 1987 and 2015. Line profiles demonstrate that the surface rotation has increased by a factor of 2 over the same interval. This is commensurate with the change in  Teff and an overall contraction. Rotation will exceed critical if contraction continues. The 1987 spectrum shows evidence of a very high abundance of the s-process element strontium. The very rapid evolution, non-negligible surface hydrogen and high surface strontium point to a history involving a very late thermal pulse. Observations over the next 30 yr should look for a decreasing pulsation period, reactivation of R CrB-type activity as the star seeks to shed angular momentum and increasing illumination by emission lines from nebular material ejected in the past.

scholarly journals The EBLM project – VII. Spin–orbit alignment for the circumbinary planet host EBLM J0608-59 A/TOI-1338 A

2020 ◽  
Vol 497 (2) ◽  
pp. 1627-1633 ◽  
Author(s):  
Vedad Kunovac Hodžić ◽  
Amaury H M J Triaud ◽  
David V Martin ◽  
Daniel C Fabrycky ◽  
Heather M Cegla ◽  
...  
Keyword(s):  
Rotation Period ◽  
Primary Component ◽  
High Resolution Spectroscopy ◽  
Spin Orbit ◽  
Primary Star ◽  
Secondary Star ◽  
Short Period ◽  
Low Mass ◽  
Detached Binaries ◽  
Binary Orbit

ABSTRACT A dozen short-period detached binaries are known to host transiting circumbinary planets. In all circumbinary systems so far, the planetary and binary orbits are aligned within a couple of degrees. However, the obliquity of the primary star, which is an important tracer of their formation, evolution, and tidal history, has only been measured in one circumbinary system until now. EBLM J0608-59/TOI-1338 is a low-mass eclipsing binary system with a recently discovered circumbinary planet identified by TESS. Here, we perform high-resolution spectroscopy during primary eclipse to measure the projected stellar obliquity of the primary component. The obliquity is low, and thus the primary star is aligned with the binary and planetary orbits with a projected spin–orbit angle β = 2${_{.}^{\circ}}$8 ± 17${_{.}^{\circ}}$1. The rotation period of 18.1 ± 1.6 d implied by our measurement of vsin i⋆ suggests that the primary has not yet pseudo-synchronized with the binary orbit, but is consistent with gyrochronology and weak tidal interaction with the binary companion. Our result, combined with the known coplanarity of the binary and planet orbits, is suggestive of formation from a single disc. Finally, we considered whether the spectrum of the faint secondary star could affect our measurements. We show through simulations that the effect is negligible for our system, but can lead to strong biases in vsin i⋆ and β for higher flux ratios. We encourage future studies in eclipse spectroscopy test the assumption of a dark secondary for flux ratios ≳1 ppt.

scholarly journals Improved hydrodynamic pulsation models for the pulsating extreme helium star V652 Herculis

2021 ◽  
Author(s):  
C Simon Jeffery ◽  
Pilar Montañés-Rodríguez ◽  
Hideyuki Saio
Keyword(s):  
Large Amplitude ◽  
Strong Shock ◽  
Model Space ◽  
Shock Acceleration ◽  
Pulsation Period ◽  
Hydrodynamic Models ◽  
Velocity Amplitude ◽  
Minimum Radius ◽  
Large Phase ◽  
Helium Star

Abstract New non-linear hydrodynamic models have been constructed to simulate the radial pulsations observed in the extreme helium star V652 Her. These use a finer zoning to allow higher radial resolution than in previous simulations. Models incorporate updated OPAL and OP opacity tables and adopt a composition based on the best atmospheric analyses to date. Key pulsation properties including period, velocity amplitude and shock acceleration are examined as a function of the mean stellar parameters (mass, luminosity, and effective temperature). The new models confirm that, for large amplitude pulsations, a strong shock develops at minimum radius, and is associated with a large phase delay between maximum brightness and minimum radius. Using the observed pulsation period to constrain parameter space in one dimension, other pulsation properties are used to constrain the model space further, and to critically discuss observational measurements. Similar models may be useful for the interpretation of other blue large amplitude pulsators, which may also exhibit pulsation-driven shocks.

scholarly journals White Dwarfs and Planetary Central Stars

1989 ◽  
Vol 131 ◽  
pp. 545-554
Author(s):  
James Liebert
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
High Surface ◽  
Planetary Nebulae ◽  
Hydrogen Atmosphere ◽  
Surface Gravity ◽  
Surface Hydrogen ◽  
Central Stars

Studies of hot white dwarf samples constrain the properties and evolution of planetary nuclei and the nebulae. In particular, the white dwarf and planetary nebulae formation rates are compared. I discuss the overlap of the sequences of white dwarfs having hydrogen (DA) and helium-rich (DO) atmospheres with known central stars of high surface gravity. There is evidence that the hydrogen atmosphere nuclei have “thick” outer hydrogen layers (≳ 10−4 M⊙), but that DA white dwarfs may have surface hydrogen layers orders of magnitude thinner. Finally, a DA planetary nucleus is discussed (0950+139) which has undergone a late nebular ejection; this object may be demonstrating that a hydrogen layer can be lost even after the star has entered the white dwarf cooling sequence.

Ftir Studies of Water and Ammonia Decomposition on Silicon Surfaces

1990 ◽  
Vol 204 ◽  
Author(s):  
A.C. Dillon ◽  
P. Gupta ◽  
M.B. Robinson ◽  
A.S. Bracker ◽  
S.M. George
Keyword(s):  
Silicon Surface ◽  
Silicon Oxide ◽  
High Surface ◽  
High Vacuum ◽  
High Surface Area ◽  
Ftir Spectra ◽  
Ultra High Vacuum ◽  
Silicon Surfaces ◽  
Surface Species ◽  
Surface Hydrogen

ABSTRACTFourier transform infrared (FTIR) transmission spectroscopy. was used to monitor the decomposition of H2O (D2O) and NH3(ND3) on silicon surfaces. Experiments were performed in-situ in an ultra-high vacuum (UHV) chamber using high surface area poroussilicon samples. The FTIR spectra revealed that H2O dissociates upon adsorption at 300K to form SiH and SiNH2 surface species. NH3 also issociates upon adsorption at 300 K to form SiH and SiOH2 species. Silicon samples with saturation exposures of H2O and NH3 were progressively annealed from 300 K to 860 K. The FTIR spectra of an H2O-saturated silicon surface revealed that the SiOH species decomposed to form a silicon oxide species and additional surface hydrogen between 460 K and 580 K. Likewise, the SiNH2 species decomposed between 540 K and 660 K to produce silicon nitride and additional surface hydrogen. In both cases, the Sill surface species decreased as H2 desorption from the silicon surface was observed above 700 K.

scholarly journals A snapshot of the inner dusty regions of a R CrB-type variable

2007 ◽  
Vol 466 (2) ◽  
pp. L1-L4 ◽  
Author(s):  
I. C. Leão ◽  
P. de Laverny ◽  
O. Chesneau ◽  
D. Mékarnia ◽  
J. R. De Medeiros
Keyword(s):  
Type Variable ◽  
R Crb Type

Symbiotic Nova PU Vul - 33 Years of Observations

2012 ◽  
Vol 21 (1-2) ◽  
Author(s):  
S. Shugarov ◽  
D. Chochol ◽  
E. Kolotilov
Keyword(s):  
Binary System ◽  
Light Curves ◽  
Secondary Minimum ◽  
Pulsation Period ◽  
Primary Minimum ◽  
Cool Component ◽  
Period Analysis ◽  
Binary Orbit ◽  
Orbit Period

AbstractWe present UBVRI light curves of the symbiotic nova PU Vul after its outburst in 1978. Three observed eclipses of the hot component by the cool one were used to determine the ephemeris of the binary system as JD (Min I) = 2444550(15) + 4897(10) × E days. the 194-day shift of the secondary minimum from its expected positions in 2001 suggests the eccentricity of the binary orbit. Period analysis of the VRI photometry improved the pulsation period of the cool AGB variable in the system to P = 217.7 days. Pulsation of the cool component is detected only in the phases around the primary minimum, when the visible hemisphere of the AGB star is not influenced by the interaction with the hot component.

scholarly journals Galactic or extragalactic chemical tagging for NGC 3201?

2018 ◽  
Vol 614 ◽  
pp. A146 ◽  
Author(s):  
B. Dias ◽  
I. Araya ◽  
J. P. Nogueira-Cavalcante ◽  
L. Saker ◽  
A. Shokry
Keyword(s):  
High Resolution ◽  
Globular Cluster ◽  
High Resolution Spectroscopy ◽  
Low Resolution ◽  
Element Abundances ◽  
Giant Stars ◽  
Mass Size ◽  
Red Giant ◽  
Process Element ◽  
Size Relation

Context. The origin of the globular cluster (GC) NGC 3201 is under debate. Its retrograde orbit points to an extragalactic origin, but no further chemical evidence supports this idea. Light-element chemical abundances are useful to tag GCs and can be used to shed light on this discussion. Aims. Recently it was shown that the CN and CH indices are useful to identify GCs that are anomalous to those typically found in the Milky Way. A possible origin of anomalous clusters is the merger of two GCs and/or the nucleus of a dwarf galaxy. We aim to derive CN and CH band strengths for red giant stars in NGC3201 and compare these with photometric indices and high-resolution spectroscopy and discuss in the context of GC chemical tagging. Methods. We measure molecular band indices of S(3839) and G4300 for CN and CH, respectively from low-resolution spectra of red giant stars. Gravity and temperature effects are removed. Photometric indices are used to indicate further chemical information on C+N+O or s-process element abundances that are not derived from low-resolution spectra. Results. We found three groups in the CN–CH distribution. A main sequence (S1), a secondary less-populated sequence (S2), and a group of peculiar (pec) CN-weak and CH-weak stars, one of which was previously known. The three groups seem to have different C+N+O and/or s-process element abundances, to be confirmed by high-resolution spectroscopy. These are typical characteristics of anomalous GCs. The CN distribution of NGC 3201 is quadrimodal, which is more common in anomalous clusters. However, NGC 3201 does not belong to the trend of anomalous GCs in the mass-size relation. Conclusions. The globular cluster NGC 3201 shows signs that it can be chemically tagged as anomalous: it has an unusual CN–CH relation, indications that pec-S1-S2 is an increasing sequence of C+N+O or s-process element abundances, and a multi-modal CN distribution that seems to correlate with s-process element abundances. The non-anomalous characteristics are that it has a debatable Fe-spread and it does not follow the trend of mass size of all anomalous clusters. Three scenarios are postulated here: (i) if the sequence pec-S1-S2 has increasing C+N+O and s-process element abundances, NGC 3201 would be the first anomalous GC outside of the mass-size relation; (ii) if the abundances are almost constant, NGC 3201 would be the first non-anomalous GC with multiple CN–CH anti-correlation groups; or (iii) it would be the first anomalous GC without variations in C+N+O and s-process element abundances. In all cases, the definition of anomalous clusters and the scenario in which they have an extragalactic origin must be revised.

scholarly journals V363 Cassiopeiae: a new lithium-rich Galactic Cepheid

2020 ◽  
Vol 639 ◽  
pp. L4 ◽  
Author(s):  
G. Catanzaro ◽  
V. Ripepi ◽  
G. Clementini ◽  
F. Cusano ◽  
G. De Somma ◽  
...  
Keyword(s):  
Main Sequence ◽  
High Resolution Spectroscopy ◽  
Pulsation Period ◽  
Historical Time ◽  
Instability Strip ◽  
Lithium Abundance ◽  
Classical Cepheids ◽  
Astrophysical Objects ◽  
Metal Abundances

Context. Classical Cepheids (DCEPs) are important astrophysical objects not only as standard candles in the determination of the cosmic distance ladder, but also as a testbed for the stellar evolution theory. This is based on the strict connection between their pulsation (period(s) and amplitudes) and stellar parameters (luminosity, mass, effective temperature, and metallicity). Aims. We examine the nature of the Galactic DCEP V363 Cas and other DCEPs that show cosmic abundances of lithium in their atmospheres. Methods. We collected three epochs of high-resolution spectroscopy for V363 Cas with HARPS-N at the TNG. We measured accurate stellar parameters: the effective temperatures, gravities, microturbulences, radial velocities, and metal abundances. Results. We detected a lithium abundance of A(Li) = 2.86 ± 0.10 dex, along with iron, carbon, and oxygen abundances of [Fe/H] = −0.30 ± 0.12 dex, [C/H] = −0.06 ± 0.15 dex, and [O/H] = 0.00 ± 0.12 dex. V363 Cas is the fifth of the Milky Way DCEPs to exhibit a Li-rich feature. An analysis of historical time-series spanning a 100-year interval shows that the period of V363 Cas is increasing, with a sharp acceleration after HJD = 2 453 000 days. This is a clear indication of a first crossing of the instability strip. Conclusions. Our results favour the scenario in which the five Galactic Li-rich DCEPs are on their first crossing of the instability strip and have had slowly rotating progenitors during their main-sequence phase.

scholarly journals The flux-weighted gravity-luminosity relation of Galactic classical Cepheids

2020 ◽  
Vol 640 ◽  
pp. A113
Author(s):  
M. A. T. Groenewegen
Keyword(s):  
High Resolution ◽  
Effective Temperature ◽  
Spectroscopic Studies ◽  
High Resolution Spectroscopy ◽  
Spectral Energy ◽  
Pulsation Period ◽  
Instability Strip ◽  
Energy Distributions ◽  
Classical Cepheids ◽  
Good Agreement

The flux-weighted gravity-luminosity relation (FWGLR) is investigated for a sample of 477 classical Cepheids (CCs), including stars that have been classified in the literature as such but are probably not. The luminosities are taken from the literature, based on the fitting of the spectral energy distributions (SEDs) assuming a certain distance and reddening. The flux-weighted gravity (FWG) is taken from gravity and effective temperature determinations in the literature based on high-resolution spectroscopy. There is a very good agreement between the theoretically predicted and observed FWG versus pulsation period relation that could serve in estimating the FWG (and log g) in spectroscopic studies with a precision of 0.1 dex. As was known in the literature, the theoretically predicted FWGLR relation for CCs is very tight and is not very sensitive to metallicity (at least for LMC and solar values), rotation rate, and crossing of the instability strip. The observed relation has a slightly different slope and shows more scatter (0.54 dex). This is due both to uncertainties in the distances and to the pulsation phase averaged FWG values. Data from future Gaia data releases should reduce these errors, and then the FWGLR could serve as a powerful tool in Cepheid studies.

scholarly journals High Resolution Spectroscopy of Six New Extreme Helium Stars

1985 ◽  
Vol 87 ◽  
pp. 67-72
Author(s):  
U. Heber ◽  
G. Jonas ◽  
J.S. Drilling
Keyword(s):  
Chemical Composition ◽  
High Resolution ◽  
Effective Temperature ◽  
Surface Gravity ◽  
High Resolution Spectroscopy ◽  
Mass Ratio ◽  
Helium Stars ◽  
Helium Star ◽  
Eddington Limit

AbstractHigh resolution spectra of six newly discovered extreme helium stars are presented. LSS 5121 is shown to be a spectroscopical twin of the hot extreme helium star HD 160641. A preliminary LTE analysis of LSS 3184 yielded an effective temperature of 22000 K and a surface gravity of log g = 3.2. Four stars form a new subgroup, classified by sharp-lined He I spectra and pronounced 0 II spectra, and it is conjectured that these lie close to the Eddington limit. The whole group of extreme helium stars apparently is inhomogenous with respect to luminosity to mass ratio and chemical composition.

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