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Start Over Subject peculiar variable stars Publisher CDS Content Level Research
1. Abundance analyses of V652 Her and HD 144941
ID:
ivo://CDS.VizieR/J/ApJ/847/127
Title:
Abundance analyses of V652 Her and HD 144941
Short Name:
J/ApJ/847/127
Date:
21 Oct 2021
Publisher:
CDS
Description:
Optical high-resolution spectra of V652 Her and HD 144941, the two extreme helium stars with exceptionally low C/He ratios, have been subjected to a non-LTE abundance analysis using the tools TLUSTY and SYNSPEC. Defining atmospheric parameters were obtained from a grid of non-LTE atmospheres and a variety of spectroscopic indicators including HeI and HeII line profiles, and the ionization equilibrium of ion pairs such as CII/CIII and NII/NIII. The various indicators provide a consistent set of atmospheric parameters: Teff=25000+/-300K, logg=3.10+/-0.12(cgs), and {xi}=13+/-2km/s are provided for V652 Her, and Teff=22000+/-600K, logg=3.45+/-0.15(cgs), and {xi}=10km/s are provided for HD 144941. In contrast to the non-LTE analyses, the LTE analyses-LTE atmospheres and an LTE line analysis-with the available indicators do not provide a consistent set of atmospheric parameters. The principal non-LTE effect on the elemental abundances is on the neon abundance. It is generally considered that these extreme helium stars with their very low C/He ratio result from the merger of two helium white dwarfs. Indeed, the derived composition of V652 Her is in excellent agreement with predictions by Zhang & Jeffery (2012MNRAS.419..452Z), who model the slow merger of helium white dwarfs; a slow merger results in the merged star having the composition of the accreted white dwarf. In the case of HD 144941, which appears to have evolved from metal-poor stars, a slow merger is incompatible with the observed composition but variations of the merger rate may account for the observed composition. More detailed theoretical studies of the merger of a pair of helium white dwarfs are to be encouraged.
2. Abundances in Ba stars
ID:
ivo://CDS.VizieR/J/A+A/525/A63
Title:
Abundances in Ba stars
Short Name:
J/A+A/525/A63
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present abundances of Mn, Cu, Zn, and various light and heavy elements for a sample of barium and normal giant stars, and present correlations between abundances contributed to different degrees by the weak-s, main-s, and r-processes of neutron capture, between Fe-peak elements and heavy elements. All spectra for the sample stars were obtained with the 1.52m telescope at ESO, La Silla, using the Fiber Fed Extended Range Optical Spectrograph (FEROS). FEROS spectra have a constant resolving power of R=48000 from 3600{AA} to 9200{AA}. The stellar sample targeted in our study includes eight mild and classical barium stars and six normal giants, with a spectral S/N ratio ranging from 200 to 450 in the visible range.
3. Abundances of 5 Ap/Bp stars of NGC 6475
ID:
ivo://CDS.VizieR/J/MNRAS/376/361
Title:
Abundances of 5 Ap/Bp stars of NGC 6475
Short Name:
J/MNRAS/376/361
Date:
21 Oct 2021
Publisher:
CDS
Description:
The connection between age, rotation and chemical abundance of magnetic Ap stars is poorly understood. Using open clusters, we are able to study samples of stars that are both coeval and co-environmental. By determining rotation and chemical abundance for Ap star members of clusters with various ages, the variations of these properties as a function of age and environment can be derived. All four probable Ap star members of the open cluster NGC 6475, as well as one normal late B star, were studied using detailed spectrum synthesis of high-resolution UVES-POP spectra. Probable cluster membership was confirmed for all five stars; however, chemical abundance anomalies only appear to be present in spectra of three. Projected rotational velocity and chemical abundances for 21 elements ranging from C to Eu are presented for the five stars. In the three peculiar stars, we find overabundances of Si, Cr, Mn, Fe and rare earths, such as Nd, characteristic of Ap stars. The set of chemically peculiar stars show fairly homogeneous abundance tables, however, notable differences exist for a few elements. There also exist appreciable differences in the vsini and main-sequence evolutionary stage of the chemically peculiar stars. This may hint at the underlying processes giving rise to the observed abundance anomalies. With this first detailed study of chemical abundances of a complete sample of magnetic Ap/Bp stars in an open cluster, we have initiated an exploration of the environmental and evolutionary influence on chemical peculiarity.
4. Abundances of HR 4487, 14 Hyd and 3 Cen A
ID:
ivo://CDS.VizieR/J/A+AS/129/563
Title:
Abundances of HR 4487, 14 Hyd and 3 Cen A
Short Name:
J/A+AS/129/563
Date:
21 Oct 2021
Publisher:
CDS
Description:
Ussing CASLEO echelle spectrograms, elemental abundances are derived for the sharp-lined non-magnetic CP stars HR 4487, 14 Hya and 3 Cen A. The first two stars are members of the Mercury-Manganese subgroup and have abundances which are similar to other such peculiar stars. The third is a hotter related star. The detection of Mn II lines in its spectrum adds to this relationship.
5. Abundances of mu Lep, 7 Sex, HR 4817 & 28 Her
ID:
ivo://CDS.VizieR/J/A+AS/125/219
Title:
Abundances of mu Lep, 7 Sex, HR 4817 & 28 Her
Short Name:
J/A+AS/125/219
Date:
21 Oct 2021
Publisher:
CDS
Description:
Elemental abundances are derived for four sharp-lined stars, the Mercury-Manganese stars {mu} Lep, HR 4817, and 28 Her, and 7 Sex, a Population I star with Population II space motions, using REOSC echelle spectrograms obtained at CASLEO to extend previous studies. Comparisons with published equivalent widths indicate that the CASLEO scale is marginally larger than those of DAO Reticon and KPNO CCD spectra. The CASLEO spectrograms have improved the quality of the abundance determinations. New abundances are found for a few elements.
6. Abundances of 6 suspected CP stars
ID:
ivo://CDS.VizieR/J/MNRAS/368/247
Title:
Abundances of 6 suspected CP stars
Short Name:
J/MNRAS/368/247
Date:
21 Oct 2021
Publisher:
CDS
Description:
The abundance pattern of six stars classified as suspected chemically peculiar in the General Catalogue of Ap and Am stars (<III/162>) by Renson has been derived to ascertain the real nature of these objects. Spectroscopic observations in the range {lambda}{lambda}4800-5600{AA} have been carried out at the stellar station of the INAF Catania Astrophysical Observatory. Among the studied stars, for only three of them we confirmed their peculiarity, HD 155102 being a silicon star, HD 159082 a mercury-manganese star and HD 162132 a moderate metallic A-type star. The other three objects have chemical abundances not so different from the standard values derived in the literature for A-type stars and, furthermore, they do not show light variability. Hence, we suggest that they could be ruled out from Renson's catalogue.
7. Abundances of the brightest member of Tuc III
ID:
ivo://CDS.VizieR/J/ApJ/838/44
Title:
Abundances of the brightest member of Tuc III
Short Name:
J/ApJ/838/44
Date:
21 Oct 2021
Publisher:
CDS
Description:
Chemically peculiar stars in dwarf galaxies provide a window for exploring the birth environment of stars with varying chemical enrichment. We present a chemical abundance analysis of the brightest star in the newly discovered ultra-faint dwarf galaxy candidate TucanaIII. Because it is particularly bright for a star in an ultra-faint Milky Way (MW) satellite, we are able to measure the abundance of 28 elements, including 13 neutron-capture species. This star, DESJ235532.66-593114.9 (DES J235532), shows a mild enhancement in neutron-capture elements associated with the r-process and can be classified as an r-I star. DES J235532 is the first r-I star to be discovered in an ultra-faint satellite, and Tuc III is the second extremely low-luminosity system found to contain r-process enriched material, after Reticulum II. Comparison of the abundance pattern of DES J235532 with r-I and r-II stars found in other dwarf galaxies and in the MW halo suggests a common astrophysical origin for the neutron-capture elements seen in all r-process enhanced stars. We explore both internal and external scenarios for the r-process enrichment of Tuc III and show that with abundance patterns for additional stars, it should be possible to distinguish between them.
8. ACV variables in the Zwicky Transient Facility
ID:
ivo://CDS.VizieR/J/A+A/656/A125
Title:
ACV variables in the Zwicky Transient Facility
Short Name:
J/A+A/656/A125
Date:
16 Mar 2022 00:55:18
Publisher:
CDS
Description:
The present work presents a case study of known variables from the Zwicky Transient Facility (ZTF) survey, with the aim of investigating the survey's suitability for the detection and study of new ACV variables. Using suitable selection criteria based on the known characteristics of ACV variables, candidate ACV stars were selected from the ZTF Catalog of Periodic Variable Stars. All light curves were inspected in detail to select the most promising candidates. Where available, low-resolution spectra from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) were employed to classify the stars on the MK system and confirm their status as mCP stars. We have identified 86 new promising ACV star candidates. 15 of these stars have LAMOST spectra available, which, in all cases, confirm them as classical mCP stars, which highlights the viability of our approach. We present astrophysical parameters for all sample stars, which can be sorted into four subgroups characterized by distinct light curve shapes. Anti-phase variations in different photometric passbands, in particular, is a unique characteristic of a subset of ACV stars readily usable for their identification. The availability of data in three different passbands (g, r, and i) is a major advantage of the ZTF survey. On the basis of our experience with other photometric surveys and the analysis of light curves, we conclude that the ZTF is well suited for the search for, and the analysis of, ACV variables, which, however, are not considered in the available ZTF variable star catalogues. Further work will be concerned with the development and refinement of a search algorithm to correctly identify these stars in ZTF data and, subsequently, in massive photometric time-series databases in general.
9. AH Cam
ID:
ivo://CDS.VizieR/J/AJ/107/679
Title:
AH Cam
Short Name:
J/AJ/107/679
Date:
21 Oct 2021
Publisher:
CDS
Description:
Analysis of 746 new V-band observations of the RR Lyrae star AH Cam obtained during 1989-1992 clearly show that its light curve cannot be described by a single period. In fact, at first glance, the Fourier spectrum of the photometry resembles that of a double-mode pulsator, with peaks at a fundamental period of 0.3686d and an apparent secondary period of 0.2628d. Nevertheless, the dual-mode solution is a poor fit to the data. Rather, we believe that AH Cam is a single-mode RR Lyrae star undergoing the Blazhko effect: periodic modulation of the amplitude and shape of its light curve. What was originally taken to be the period of the second mode is instead the 1-cycle/d alias of a modulation sidelobe in the Fourier spectrum. The data are well described by a modulation period of just under 11d, which is the shortest Blazhko period reported to date in the literature and confirms the earlier suggestion by Goranskii. A low-resolution spectrum of AH Cam indicates that it is relatively metal rich, with {DELTA}S<=2. Its high metallicity and short modulation period may provide a critical test of at least one theory for the Blazhko effect. Moskalik's internal resonance model makes specific predictions of the growth rate of the fundamental mode vs fundamental period. AH Cam falls outside the regime of other known Blazhko variables and resonance model predictions, but these are appropriate for metal-poor RR Lyrae stars. If the theory matches the behavior of AH Cam for a metal-rich stellar model, this would bolster the resonance hypothesis.
10. {alpha} Scl and HD 170973 abundances
ID:
ivo://CDS.VizieR/J/A+A/367/859
Title:
{alpha} Scl and HD 170973 abundances
Short Name:
J/A+A/367/859
Date:
21 Oct 2021
Publisher:
CDS
Description:
Fine analyses of the magnetic CP stars {alpha} Scl and HD 170973 are presented using ATLAS9 model atmospheres which have same bulk metallicity as the deduced abundances. The light elements are mostly solar except for silicon, and all the heavier elements except nickel in HD 170973, which is solar, are greatly overabundant. The iron peak elements are typically 10 times overabundant, Sr is of order of 1000 times solar, Y and Zr are of order of 100 times solar. The rare earths are 1000 or more times overabundant.

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