- ID:
- ivo://CDS.VizieR/J/A+A/619/A130
- Title:
- Solar sibling candidates chemical abundances
- Short Name:
- J/A+A/619/A130
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Finding solar siblings, that is, stars that formed in the same cluster as the Sun, will yield information about the conditions at the Sun's birthplace. Finding possible solar siblings is difficult since they are spread widely throughout the Galaxy. We search for solar sibling candidates in AMBRE, the very large spectra database of solar vicinity stars. Since the ages and chemical abundances of solar siblings are very similar to those of the Sun, we carried out a chemistry- and age-based search for solar sibling candidates. We used high-resolution spectra to derive precise stellar parameters and chemical abundances of the stars. We used these spectroscopic parameters together with Gaia DR2 astrometric data to derive stellar isochronal ages. Gaia data were also used to study the kinematics of the sibling candidates. From the about 17000 stars that are characterized within the AMBRE project, we first selected 55 stars whose metallicities are closest to the solar value (-0.1<=[Fe/H]<=0.1dex). For these stars we derived precise chemical abundances of several iron-peak, {alpha}- and neutron-capture elements, based on which we selected 12 solar sibling candidates with average abundances and metallicities between -0.03 to 0.03dex. Our further selection left us with 4 candidates with stellar ages that are compatible with the solar age within observational uncertainties. For the 2 of the hottest candidates, we derived the carbon isotopic ratios, which are compatible with the solar value. HD186302 is the most precisely characterized and probably the most probable candidate of our 4 best candidates. Very precise chemical characterization and age estimation is necessary to identify solar siblings. We propose that in addition to typical chemical tagging, the study of isotopic ratios can give further important information about the relation of sibling candidates with the Sun. Ideally, asteroseismic age determinations of the candidates could solve the problem of imprecise isochronal ages.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/787/10
- Title:
- Solar s-process contributions with GCE model
- Short Name:
- J/ApJ/787/10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the s-process abundances (A>~90) at the epoch of the solar system formation. Asymptotic giant branch yields are computed with an updated neutron capture network and updated initial solar abundances. We confirm our previous results obtained with a Galactic chemical evolution (GCE) model: (1) as suggested by the s-process spread observed in disk stars and in presolar meteoritic SiC grains, a weighted average of s-process strengths is needed to reproduce the solar s distribution of isotopes with A>130; and (2) an additional contribution (of about 25%) is required in order to represent the solar s-process abundances of isotopes from A=90 to 130. Furthermore, we investigate the effect of different internal structures of the ^13^C pocket, which may affect the efficiency of the ^13^C({alpha},n)^16^O reaction, the major neutron source of the s process. First, keeping the same ^13^C profile adopted so far, we modify by a factor of two the mass involved in the pocket; second, we assume a flat ^13^C profile in the pocket, and we test again the effects of the variation of the mass of the pocket. We find that GCE s predictions at the epoch of the solar system formation marginally depend on the size and shape of the ^13^C pocket once a different weighted range of ^13^C-pocket strengths is assumed. We obtain that, independently of the internal structure of the ^13^C pocket, the missing solar system s-process contribution in the range from A=90 to 130 remains essentially the same.
- ID:
- ivo://CDS.VizieR/J/A+A/619/A73
- Title:
- Solar Twins age-chromospheric activity
- Short Name:
- J/A+A/619/A73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It is well known that the magnetic activity of solar-type stars decreases with age, but it is widely debated in the literature whether there is a smooth decline or if there is an early sharp drop until 1-2Gyr that is followed by a relatively inactive constant phase. We revisited the activity-age relation using time-series observations of a large sample of solar twins whose precise isochronal ages and other important physical parameters have been determined. We measured the CaII H and K activity indices using 9000 HARPS spectra of 82 solar twins. In addition, the average solar activity was calculated through asteroids and Moon reflection spectra using the same instrumentation. Thus, we transformed our activity indices into the S Mount Wilson scale (S_MW_), recalibrated the Mount Wilson absolute flux and photospheric correction equations as a function of Te, and then computed an improved bolometric flux normalized activity index logR'_HK_(Teff) for the entire sample. New relations between activity and the age of solar twins were derived by assessing the chromospheric age-dating limits using logR'_HK_(Teff). We measured an average solar activity of S_MW_=0.1712+/-0.0017 during solar magnetic cycles 23-24 covered by HARPS observations, and we also inferred an average of S_MW_=0.1694+/-0.0025 for cycles 10-24, anchored on a sunspot number correlation of S index versus. We also found a simple relation between the average and the dispersion of the activity levels of solar twins. This enabled us to predict the stellar variability effects on the age-activity diagram, and consequently, to estimate the chromospheric age uncertainties that are due to the same phenomena. The age-activity relation is still statistically significant up to ages around 6-7Gyr, in agreement with previous works using open clusters and field stars with precise ages. Our research confirms that CaII H& K lines remain a useful chromospheric evolution tracer until stars reach ages of at least 6-7Gyr. We found evidence that for the most homogenous set of old stars, the chromospheric activity indices seem to continue to decrease after the solar age toward the end of the main sequence. Our results indicate that a significant part of the scatter observed in the age-activity relation of solar twins can be attributed to stellar cycle modulations eects. The Sun seems to have a normal activity level and variability for its age.
- ID:
- ivo://CDS.VizieR/J/A+A/587/A131
- Title:
- Solar twins in the ELODIE archive
- Short Name:
- J/A+A/587/A131
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A large dataset of ~2800 spectra extracted from the ELODIE archive was analysed in order to find solar twins. Stellar spectra closely resembling the spectrum of the Sun were selected by applying a purely differential method, directly on the fluxes. As solar reference, 18 spectra of asteroids, of the Moon, and of the blue sky were used. Atmospheric parameters and differential abundances of eight chemical elements were determined for the solar twin candidates after a careful selection of appropriate lines. The Li feature of the targets was investigated and additional information on absolute magnitude and age was gathered from the literature. HIP076114 (HD138573) is our best twin candidate; it looks exactly like the Sun in all these properties.
- ID:
- ivo://CDS.VizieR/J/MNRAS/417/1823
- Title:
- Sombrero galaxy globular clusters
- Short Name:
- J/MNRAS/417/1823
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a large sample of over 200 integrated-light spectra of confirmed globular clusters (GCs) associated with the Sombrero (M104) galaxy taken with the Deep Imaging Multi-Object Spectrograph (DEIMOS) instrument on the Keck telescope. A significant fraction of the spectra have signal-to-noise ratio levels high enough to allow measurements of GC metallicities using the method of Brodie & Huchra. We find a distribution of spectroscopic metallicities in the range -2.2<[Fe/H]<+0.1 that is bimodal, with peaks at [Fe/H]~-1.4 and -0.6. Thus, the GC system of the Sombrero galaxy, like a few other galaxies now studied in detail, reveals a bimodal spectroscopic metallicity distribution supporting the long-held belief that colour bimodality reflects two metallicity subpopulations. This further suggests that the transformation from optical colour to metallicity for old stellar populations, such as GCs, is not strongly non-linear. We also explore the radial and magnitude distribution with metallicity for GC subpopulations but small number statistics prevent any clear trends in these distributions.
- ID:
- ivo://CDS.VizieR/J/A+A/597/A10
- Title:
- South Ecliptic Pole stars radial velocities
- Short Name:
- J/A+A/597/A10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an initial overview of the targets to be found in the 1-square-degree SEP region that was observed repeatedly by Gaia ever since its commissioning. In our representative sample, we identified one galaxy, six LMC S-stars, nine candidate chromospherically active stars, and confirmed the status of 18 LMC Carbon stars. A careful study of the 3471 epoch radial velocity measurements led us to identify 145 RV constant stars with radial velocities varying by less than 1km/s. Seventy-eight stars show significant RV scatter, while nine stars show a composite spectrum. As expected, the distribution of the RVs exhibits two main peaks that correspond to Galactic and LMC stars. By combining [Fe/H], and logg, estimates, and RV determinations, we identified 203 members of the LMC, while 51 more stars are candidate members.
- ID:
- ivo://CDS.VizieR/J/A+A/587/A2
- Title:
- SP_Ace derived data from stellar spectra
- Short Name:
- J/A+A/587/A2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Ongoing and future massive spectroscopic surveys will collect large numbers (10^6^-10^7^) of stellar spectra that need to be analyzed. Highly automated software is needed to derive stellar parameters and chemical abundances from these spectra. We developed a new method of estimating the stellar parameters Teff, logg, [M/H], and elemental abundances. This method was implemented in a new code, SP_Ace (Stellar Parameters And Chemical abundances Estimator). This is a highly automated code suitable for analyzing the spectra of large spectroscopic surveys with low or medium spectral resolution (R=2000-20000). After the astrophysical calibration of the oscillator strengths of 4643 absorption lines covering the wavelength ranges 5212-6860{AA} and 8400-8924{AA}, we constructed a library that contains the equivalent widths (EW) of these lines for a grid of stellar parameters. The EWs of each line are fit by a polynomial function that describes the EW of the line as a function of the stellar parameters. The coefficients of these polynomial functions are stored in a library called the "GCOG library". SP_Ace, a code written in FORTRAN95, uses the GCOG library to compute the EWs of the lines, constructs models of spectra as a function of the stellar parameters and abundances, and searches for the model that minimizes the {chi}^2^ deviation when compared to the observed spectrum. The code has been tested on synthetic and real spectra for a wide range of signal-to-noise and spectral resolutions.
- ID:
- ivo://CDS.VizieR/J/A+A/368/267
- Title:
- Spatially resolved spectroscopy of Cas A
- Short Name:
- J/A+A/368/267
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have performed the first detailed spatially resolved spectroscopy of Cas A in the 1.6-10keV energy range, using data taken with the Medium Energy Concentrator Spectrometer (MECS) on board the BeppoSAX Observatory. The well calibrated point spread function in the central region of the MECS allowed us to perform a spatial deconvolution of the data at full energy resolution. We eventually generated a set of spectra, covering a region of ~3' radius around the centre of Cas A. The data used were obtained on Aug 1996, Sep 1996 and Nov 1997.
- ID:
- ivo://CDS.VizieR/J/ApJ/711/138
- Title:
- Spectral analysis of HIP 60350 and 18 Peg
- Short Name:
- J/ApJ/711/138
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Young, massive stars in the Galactic halo are widely supposed to be the result of an ejection event from the Galactic disk forcing some stars to leave their place of birth as so-called runaway stars. Here, we present a detailed spectroscopic and kinematic analysis of the runaway B star HIP 60350 to determine which runaway scenario -a supernova explosion disrupting a binary system or dynamical interaction in star clusters- may be responsible for HIP 60350's peculiar orbit. Based on a non-local thermodynamic equilibrium approach, a high-resolution optical echelle spectrum was examined to revise spectroscopic quantities and for the first time to perform a differential chemical abundance analysis with respect to the B-type star 18 Peg. The results together with proper motions from the Hipparcos Catalog further allowed the three-dimensional kinematics of the star to be studied numerically. The abundances derived for HIP 60350 are consistent with a slightly supersolar metallicity agreeing with the kinematically predicted place of birth ~6kpc away from the Galactic center. However, they do not exclude the possibility of an {alpha}-enhanced abundance pattern expected in the case of the supernova scenario. Its outstanding high Galactic rest-frame velocity of 530+/-35km/s is a consequence of ejection in the direction of Galactic rotation and slightly exceeds the local Galactic escape velocity in a standard Galactic potential. Hence, HIP 60350 may be unbound to the Galaxy.
- ID:
- ivo://CDS.VizieR/J/AJ/125/2502
- Title:
- Spectral indices of Galactic halo
- Short Name:
- J/AJ/125/2502
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present our calibration of spectroscopic measures of luminosity and metallicity for halo giant candidates and give metallicities and distances for our first sample of spectroscopically confirmed giants. These giants have distances ranging from 15 to 83kpc. As surveys reach farther into the Galaxy's halo with K giant samples, identification of giants becomes more difficult. This is because the numbers of foreground halo K dwarfs rise for V magnitudes of 19-20, typical for halo giants at 100kpc. Our photometric survey uses the strength of the Mgb/H feature near 5170{AA} to weed K dwarfs out of the disk and thick disk, but we need spectroscopic measures of the strength of the Ca II K, Ca I {lambda}4227, and Mgb/H features to distinguish between the very metal-poor dwarfs and halo giants. Using a full error analysis of our spectroscopic measures, we show why a signal-to-noise ratio of ~15pixel^-1^ at Ca I {lambda}4227 and ~10 at Ca II K is needed for reliable luminosity discrimination. We use the Ca II K and Mgb features to measure metallicity in our halo giants, with typical errors (random plus systematic) of 0.3dex for [Fe/H] values from -0.8 to -3.0.
