- ID:
- ivo://CDS.VizieR/J/A+A/649/A49
- Title:
- Spectroscopic study of CEMP-(s and r/s) stars
- Short Name:
- J/A+A/649/A49
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- The origin of the enhanced abundances of both s- and r-process elements observed in a subclass of Carbon-Enhanced Metal-Poor (CEMP) stars, i.e., CEMP-r/s stars, still remains poorly understood. The i-process nucleosynthesis has been suggested as one of the most promising mechanisms for the origin of these stars. To better understand the chemical signatures and formation mechanism(s) of five previously claimed potential CH star candidates HE 0017+0055, HE 2144-1832, HE 2339-0837, HD 145777 and CD-27 14351 through a detailed systematic follow-up spectroscopic study based on high-resolution spectra. The stellar atmospheric parameters, the effective temperature T_eff_, the microturbulent velocity {zeta}, the surface gravity logg, and the metallicity [Fe/H] are derived from local thermodynamic equilibrium analyses using model atmospheres. Elemental abundances of C, N, {alpha}-elements, iron-peak elements and several neutron-capture elements are estimated using the equivalent width measurement technique as well as spectrum synthesis calculations in some cases. In the context of the double enhancement observed in four of the programme stars, we have critically examined if the literature i-process model yields ([X/Fe]) of heavy elements can explain the observed abundance distribution. The estimated metallicity [Fe/H] of the programme stars ranges from -1.63 to -2.74. All the five stars show enhanced abundance for Ba and four of them exhibit enhanced abundance for Eu. Based on our analysis, HE 0017+0055, HE 2144-1832 and HE 2339-0837 are found to be CEMP-r/s stars, whereas HD 145777 and CD-27 14351 show characteristic properties of CEMP-s stars. From a detailed analysis of different classifiers of CEMP stars, we have identified the one which best describes the CEMP-s and CEMP-r/s stars. We found that for both CEMP-s and CEMP-r/s stars, [Ba/Eu] and [La/Eu] exhibit positive values and [Ba/Fe]>=1.0. However, CEMP-r/s stars satisfy [Eu/Fe]>=1.0, 0.0<=[Ba/Eu]<=1.0 and/or 0.0<=[La/Eu]<=0.7. CEMP-s stars normally show [Eu/Fe]<1.0 with [Ba/Eu]>0.0 and/or [La/Eu]>0.5. If [Eu/Fe]~>=1.0, then the condition on [Ba/Eu] and/or [La/Eu] for a star to be a CEMP-s star is [Ba/Eu]>1.0 and/or [La/Eu]>0.7. Using a large sample of similar stars from the literature we have examined if [hs/ls] alone can be used as a classifier, and if there are any limiting values for [hs/ls] ratio that can be used to distinguish CEMP-s and CEMP-r/s stars. In spite of peaking at different values of [hs/ls], CEMP-s and CEMP-r/s stars show an overlap in the range 0.0<[hs/ls]<1.5 ,and hence, this ratio cannot be used to distinguish CEMP-s and CEMP-r/s stars. We have noticed a similar overlap in the case of [Sr/Ba] ratio as well, in the range -1.6<[Sr/Ba]<-0.5 and hence, this ratio also cannot be used to separate the two subclasses, CEMP-s and CEMP-r/s.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/378/1507
- Title:
- Spectroscopic study of 6 galaxies
- Short Name:
- J/MNRAS/378/1507
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an examination of the kinematics and stellar populations of a sample of three brightest group galaxies (BGGs) and three brightest cluster galaxies (BCGs) in X-ray groups and clusters. We have obtained high signal-to-noise ratio Gemini/Gemini South Multi-Object Spectrograph (GMOS) long-slit spectra of these galaxies and use Lick indices to determine ages, metallicities and alpha-element abundance ratios out to at least their effective radii. We find that the BGGs and BCGs have very uniform masses, central ages and central metallicities.
- ID:
- ivo://CDS.VizieR/J/A+A/519/A40
- Title:
- Spectroscopic study of 65 nearby galaxies
- Short Name:
- J/A+A/519/A40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- With the aim of constraining the source of excitation and the origin of the ionized gas in early-type galaxies (ETGs), we analyzed intermediate resolution optical spectra of a sample of 65 ETGs mostly located in low density environments. Optical emission lines are detected in 89% of the sample. The incidence and strength of emission do not correlate either with the E/S0 classification, or with the fast/slow rotator classification. Comparing the nuclear r<r_e_/16 line emission with the classical [OIII]/Hb vs [NII]/Ha diagnostic diagram, the galaxy activity is so classified: 72% of the galaxies with emission are LINERs, 9% are Seyferts, 12% are Composite/Transition objects, and 7% are non-classified. Seyferts have young luminosity-weighted ages (<5Gyr), and appear, on average, significantly younger than LINERs and Composites. Excluding the Seyferts from our sample, we find that the spread in the ([OIII], Ha or [NII]) emission strength increases with the galaxy central velocity dispersion sigma_c_. The [NII]/Ha ratio decreases with increasing galacto-centric distance, indicating either a decrease of the nebular metallicity, or a progressive "softening" of the ionizing spectrum. The average oxygen abundance of the ionized gas is slightly less than solar, and a comparison with the results obtained in Paper III (Cat. J/A+A/463/455) from Lick indices reveals that it is ~0.2dex lower than that of stars. Conclusions: the nuclear emission can be explained with photoionization by PAGB stars alone only in ~22% of the LINERs/Composite sample. On the other hand, we can not exclude an important role of PAGB star photoionization at larger radii. For the major fraction of the sample, the nuclear emission is consistent with excitation from a low-accretion rate AGN, fast shocks (200-500km/s) in a relatively gas-poor environment (n<100cm^-3^), or coexistence of the two. The derived nebular metallicities suggest either an external origin of the gas, or an overestimate of the oxygen yields by SN models.
- ID:
- ivo://CDS.VizieR/J/AJ/135/1117
- Title:
- Spectroscopic study of red giants in M15
- Short Name:
- J/AJ/135/1117
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- High-resolution spectra of 110 selected red giant stars in the globular cluster M15 (NGC 7078) were obtained with Hectochelle at the MMT telescope in 2005 May, 2006 May, and 2006 October. Echelle orders containing H{alpha} and CaII H&K are used to identify emission and line asymmetries characterizing motions in the extended atmospheres. Emission in H{alpha} is detected to a luminosity of log(L/L_{sun}_)=2.36, in this very metal-deficient cluster, comparable to other studies, suggesting that the appearance of emission wings is independent of stellar metallicity. The faintest stars showing H{alpha} emission appear to lie on the asymptotic giant branch (AGB) in M15. A line-bisector technique for H{alpha} reveals outflowing velocities in all stars brighter than log(L/L_{sun}_)=2.5, and this outflow velocity increases with stellar luminosity, indicating the mass outflow increases smoothly with luminosity. Many stars lying low on the AGB show exceptionally high outflow velocities (up to 10-15km/s) and more velocity variability (up to 6-8km/s) than red giant branch (RGB) stars of similar apparent magnitude. High velocities in M15 may be related to the low cluster metallicity. Dusty stars identified from Spitzer Space Telescope infrared photometry as AGB stars are confirmed as cluster members by radial velocity measurements, yet their H{alpha} profiles are similar to those of RGB stars without dust. If substantial mass loss creates the circumstellar shell responsible for infrared emission, such mass loss must be episodic.
- ID:
- ivo://CDS.VizieR/J/MNRAS/450/397
- Title:
- Spectroscopic study of RGs in the Kepler field
- Short Name:
- J/MNRAS/450/397
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Thanks to the recent very high precision photometry of red giants from satellites such as Kepler, precise mass and radius values as well as accurate information of evolutionary stages are already established by asteroseismic approach for a large number of G-K giants. Based on the high-dispersion spectra of selected such 55 red giants in the Kepler field with precisely known seismic parameters (among which parallaxes are available for nine stars), we checked the accuracy of the determination method of stellar parameters previously applied to many red giants by Takeda et al. (2008PASJ...60..781T), since it may be possible to discriminate their complex evolutionary status by using the surface gravity versus mass diagram. We confirmed that our spectroscopic gravity and the seismic gravity satisfactorily agree with each other (to within ~0.1 dex) without any systematic difference. However, the mass values of He-burning red clump giants derived from stellar evolutionary tracks (~2-3 M_{sun}_) were found to be markedly larger by ~50 percent compared to the seismic values (~1-2 M_{sun}_) though such discrepancy is not seen for normal giants in the H-burning phase, which reflects the difficulty of mass determination from intricately overlapping tracks on the luminosity versus effective temperature diagram. This consequence implies that the mass results of many red giants in the clump region determined by Takeda et al. are likely to be significantly overestimated. We also compare our spectroscopically established parameters with recent literature values, and further discuss the prospect of distinguishing the evolutionary status of red giants based on the conventional (i.e. non-seismic) approach.
- ID:
- ivo://CDS.VizieR/J/A+A/391/641
- Title:
- Spectroscopic study of sigma Geminorum from IUE
- Short Name:
- J/A+A/391/641
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The IUE spectra of {sigma} Gem have been taken from the NASA IUE archive using IDL (Interactive Data Language). The spectra have been observed in 1979-1986 period. All the spectra analysed in the present study have NEWSIPS reductions and consist of 25 LWP, 8 LWR and 5 SWP images in high resolution, and 2 LWP and 14 SWP images in low dispersion. The emission lines, identified as activity indicators and originating in the chromosphere and transition region, are seen in the spectra. The emission line fluxes and equivalent widths are computed based on Gaussian profile fitting procedures to examine the existence of any line flux variation that depends on time or orbital phase. It was found that there is a flux variation with time and orbital phase that is in good agreement with the photometric light curve variation. By comparing the flux variation with simultaneous light curve variation, it can be shown that there is a relation between the ultraviolet flux variation and the spot activity of the system, as shown by Ayres et al. (1984ApJ...279..197A) and Engvold et al. (1988A&A...192..234E) based on their IUE (with IUESIPS reduction) spectral analysis. Moreover, it was inferred that there is no ultraviolet excess in {sigma} Gem by comparing the spectra of {beta} Gem taken as a comparison star. The Mg II h and k radial velocity curves of {sigma} Gem were in a good agreement with data obtained by Eker (1986MNRAS.221..947E) and Duemmler et al. (1997A&AS..123..209D).
- ID:
- ivo://CDS.VizieR/J/A+A/420/183
- Title:
- Spectroscopic survey in solar neighborhood
- Short Name:
- J/A+A/420/183
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results of a high-resolution spectroscopic survey of all the stars more luminous than M_V_=6.5mag within 14.5pc from the Sun. The Hipparcos catalog's completeness limits guarantee that our survey is comprehensive and free from some of the selection effects in other samples of nearby stars. The resulting spectroscopic database, which we have made publicly available, includes spectra for 118 stars obtained with a resolving power of R~50000, continuous spectral coverage between ~362-921nm, and typical signal-to-noise ratios in the range 150-600. We derive stellar parameters and perform a preliminary abundance and kinematic analysis of the F-G-K stars in the sample. The inferred metallicity ([Fe/H]) distribution is centered at about -0.1dex, and shows a standard deviation of 0.2dex.
- ID:
- ivo://CDS.VizieR/J/ApJ/743/138
- Title:
- Spectroscopic survey of bright white dwarfs
- Short Name:
- J/ApJ/743/138
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have conducted a spectroscopic survey of over 1300 bright (V<=17.5), hydrogen-rich white dwarfs based largely on the last published version of the McCook & Sion (1999ApJS..121....1M, Cat. III/235) catalog. The complete results from our survey, including the spectroscopic analysis of over 1100 DA white dwarfs, are presented. High signal-to-noise ratio optical spectra were obtained for each star and were subsequently analyzed using our standard spectroscopic technique where the observed Balmer line profiles are compared to synthetic spectra computed from the latest generation of model atmospheres appropriate for these stars. First, we present the spectroscopic content of our sample, which includes many misclassifications as well as several DAB, DAZ, and magnetic white dwarfs. Next, we look at how the new Stark broadening profiles affect the determination of the atmospheric parameters. When necessary, specific models and analysis techniques are used to derive the most accurate atmospheric parameters possible. In particular, we employ M dwarf templates to obtain better estimates of the atmospheric parameters for those white dwarfs that are in DA+dM binary systems.
- ID:
- ivo://CDS.VizieR/J/ApJ/498/195
- Title:
- Spectroscopic survey of CL 1358+62
- Short Name:
- J/ApJ/498/195
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a spectroscopic survey of the rich X-ray-selected galaxy cluster CL 1358+6245 at z=0.328. When our 173 new multislit spectra of cluster galaxies are combined with data from the literature, we produce a catalog of 232 cluster members in a region 10'x11' (3.5Mpcx3.8Mpc) surrounding the brightest cluster galaxy. These data are used to study the structure and dynamics of the cluster and to examine the radial and velocity distributions as a function of spectral type. We classify the spectral types of the cluster members according to the strengths of the Balmer absorption lines (H{delta}, H{gamma}, and H{beta}) and the [O II] 3727{AA} emission line.
- ID:
- ivo://CDS.VizieR/J/ApJ/834/176
- Title:
- Spectroscopic survey of M37 candidate members
- Short Name:
- J/ApJ/834/176
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a spectroscopic survey to characterize chromospheric activity, as measured by H{alpha} emission, in low-mass members of the 500Myr old open cluster M37. Combining our new measurements of H{alpha} luminosities (L_H{alpha}_) with previously cataloged stellar properties, we identify saturated and unsaturated regimes in the dependence of the L_H{alpha}_-to-bolometric luminosity ratio, L_H{alpha}_/L_bol_, on the Rossby number R_o_. All rotators with R_o_ smaller than 0.03+/-0.01 converge to an activity level of L_H{alpha}_/L_bol_=(1.27+/-0.02)x10^-4^. This saturation threshold (R_o,sat_=0.03+/-0.01) is statistically smaller than that found in most studies of the rotation-activity relation. In the unsaturated regime, slower rotators have lower levels of chromospheric activity, with L_H{alpha}_/L_bol_(R_o_) following a power-law of index {beta}=-0.51+/-0.02, slightly shallower than that found for a combined ~650Myr old sample of Hyades and Praesepe stars. By comparing this unsaturated behavior to that previously found for coronal activity in M37 (as measured via the X-ray luminosity, L_X_), we confirm that chromospheric activity decays at a much slower rate than coronal activity with increasing R_o_. While a comparison of L_H{alpha}_ and L_X_ for M37 members with measurements of both reveals a nearly 1:1 relation, removing the mass-dependencies by comparing instead L_H{alpha}_/L_bol_ and L_X_/L_bol_ does not provide clear evidence for such a relation. Finally, we find that R_o,sat_ is smaller for our chromospheric than for our coronal indicator of activity (R_o,sat_=0.03+/-0.01 versus 0.09+/-0.01). We interpret this as possible evidence for coronal stripping.
