- ID:
- ivo://CDS.VizieR/J/A+A/608/A46
- Title:
- Constraining cosmic scatter
- Short Name:
- J/A+A/608/A46
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the stellar parameters, abundances, associated errors and the linelist of a set of 23 metal-poor and very metal-poor halo stars. Stellar parameters and chemical abundances were derived in a line-by-line differential analysis from equivalent widths of UVES/VLT spectra. The differential analysis provided us unprecedented small data scatter and errors. Our sample, along with data from different authors in different metallicity ranges, allowed us to do an extensive comparison of the chemical abundances with the predictions of a Galaxy chemical evolution model.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJS/213/5
- Title:
- Cool KOIs. VI. H- and K- band spectra
- Short Name:
- J/ApJS/213/5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present H- and K-band spectra for late-type Kepler Objects of Interest (the "Cool KOIs"): low-mass stars with transiting-planet candidates discovered by NASA's Kepler Mission that are listed on the NASA Exoplanet Archive. We acquired spectra of 103 Cool KOIs and used the indices and calibrations of Rojas-Ayala et al. (2012, Cat. J/ApJ/748/93) to determine their spectral types, stellar effective temperatures, and metallicities, significantly augmenting previously published values. We interpolate our measured effective temperatures and metallicities onto evolutionary isochrones to determine stellar masses, radii, luminosities, and distances, assuming the stars have settled onto the main sequence. As a choice of isochrones, we use a new suite of Dartmouth predictions that reliably include mid-to-late M dwarf stars. We identify five M4V stars: KOI-961 (confirmed as Kepler 42), KOI-2704, KOI-2842, KOI-4290, and the secondary component to visual binary KOI-1725, which we call KOI-1725B. We also identify a peculiar star, KOI-3497, which has Na and Ca lines consistent with a dwarf star but CO lines consistent with a giant. Visible-wavelength adaptive optics imaging reveals two objects within a 1 arcsec diameter; however, the objects' colors are peculiar. The spectra and properties presented in this paper serve as a resource for prioritizing follow-up observations and planet validation efforts for the Cool KOIs.
- ID:
- ivo://CDS.VizieR/J/MNRAS/459/1170
- Title:
- Coulour-Period relation for Cepheids
- Short Name:
- J/MNRAS/459/1170
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We compare mid-infrared (IR) 3.6 and 4.5{mu}m Warm Spitzer observations for Cepheids in the Milky Way and the Large and Small Magellanic Clouds. Using models, we explore in detail the effect of the CO rotation-vibration band-head at 4.6{mu}m on the mid-IR photometry. We confirm the temperature sensitivity of the CO band-head at 4.6{mu}m and find no evidence for an effect at 3.6{mu}m. We compare the ([3.6]-[4.5]) period-colour relations in the MW, LMC and SMC. The slopes of the period-colour relations for the three galaxies are in good agreement, but there is a trend in zero-point with metallicity, with the lowest metallicity Cepheids having redder mid-IR colours. Finally, we present a colour-[Fe/H] relation based on published spectroscopic metallicities. This empirical relation, calibrated to the metallicity system of Genovali et al., demonstrates that the ([3.6]-[4.5]) colour provides a reliable metallicity indicator for Cepheids, with a precision comparable to current spectroscopic determinations.
- ID:
- ivo://CDS.VizieR/J/A+A/577/A81
- Title:
- Deep SDSS Optical Spectroscopy. II.
- Short Name:
- J/A+A/577/A81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze a sample of 3942 low-resolution (R~2000) optical spectra from the Sloan Digital Sky Survey (SDSS), focusing on stars with effective temperatures 5800<Teff<6300K, and distances from the Milky Way plane in excess of 5kpc, and determine their abundances of Fe, Ca, and Mg. This work follows the same methodology as in the previous paper in this series, deriving atmospheric parameters by chi^2^ minimization, but we now obtain the abundances of individual elements by fitting their associated spectral lines. Distances are calculated from absolute magnitudes obtained by a statistical comparison of our stellar parameters with stellar-evolution models. The observations reveal a decrease in the abundances of iron, calcium and magnesium at large distances from the Galactic center. The median abundances for the halo stars analyzed are fairly constant up to a Galactocentric distance r~20kpc, rapidly decrease between r~20 and r~40kpc, and flatten out to significantly lower values at larger distances, consistent with previous studies. In addition, we examine the Ca/Fe and Mg/Fe ratios as a function of Fe/H and Galactocentric distance. Our results show that the most distant parts of the halo show a steeper variation of the Ca/Fe and Mg/Fe with iron. We found that at the range -1.6<[Fe/H]<-0.4 the Ca/Fe ratio decreases with distance, in agreement with earlier results based on local stars. However, the opposite trend is apparent for Mg/Fe. Our conclusion that the outer regions of the halo are more metal-poor than the inner regions, based on in-situ observations of distant stars, is in concert with recent results based on inferences from the kinematics of more local stars, and with predictions of recent galaxy formation simulations for galaxies similar to the Milky Way.
- ID:
- ivo://CDS.VizieR/J/ApJ/681/1524
- Title:
- Detailed abundances for 28 metal-poor stars
- Short Name:
- J/ApJ/681/1524
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of an abundance analysis for a sample of stars with -4<[Fe/H]<-2. The data were obtained with the HIRES spectrograph at Keck Observatory. The set includes 28 stars, with effective temperature ranging from 4800 to 6600K. For 13 stars with [Fe/H]<-2.6, including nine with [Fe/H]<-3.0 and one with [Fe/H]=-4.0, these are the first reported detailed abundances. For the most metal-poor star in our sample, CS 30336-049, we measure an abundance pattern that is very similar to stars in the range [Fe/H]~-3.5, including a normal C+N, abundance. We also find that it has very low but measurable Sr and Ba, indicating some neutron-capture activity even at this low of a metallicity. We explore this issue further by examining other very neutron capture-deficient stars and find that, at the lowest levels, [Ba/Sr] exhibits the ratio of the main r-process. We also report on a new r-process-enhanced star, CS 31078-018. This star has [Fe/H]=-2.85, [Eu/Fe]=1.23, and [Ba/Eu]=-0.51. CS 31078-018 exhibits an "actinide boost," i.e., much higher [Th/Eu] than expected and at a similar level to CS 31082-001. Our spectra allow us to further constrain the abundance scatter at low metallicities, which we then use to fit to the zero-metallicity Type II supernova yields of Heger & Woosley (2008arXiv0803.3161H). We find that supernovae with progenitor masses between 10 and 20M_{sun}_ provide the best matches to our abundances.
- ID:
- ivo://CDS.VizieR/J/ApJ/886/10
- Title:
- Dwarfs or giants? Stellar metallicities & distances
- Short Name:
- J/ApJ/886/10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new fully data-driven algorithm that uses photometric data from the Canada-France Imaging Survey (CFIS; u), Pan-STARRS 1 (PS1; griz), and Gaia (G) to discriminate between dwarf and giant stars and to estimate their distances and metallicities. The algorithm is trained and tested using the Sloan Digital Sky Survey (SDSS)/SEGUE spectroscopic data set and Gaia photometric/astrometric data set. At [Fe/H]<-1.2, the algorithm succeeds in identifying more than 70% of the giants in the training/test set, with a dwarf contamination fraction below 30% (with respect to the SDSS/SEGUE data set). The photometric metallicity estimates have uncertainties better than 0.2dex when compared with the spectroscopic measurements. The distances estimated by the algorithm are valid out to a distance of at least ~80kpc without requiring any prior on the stellar distribution and have fully independent uncertainties that take into account both random and systematic errors. These advances allow us to estimate these stellar parameters for approximately 12 million stars in the photometric data set. This will enable studies involving the chemical mapping of the distant outer disk and the stellar halo, including their kinematics using the Gaia proper motions. This type of algorithm can be applied in the southern hemisphere to the first release of LSST data, thus providing an almost complete view of the external components of our Galaxy out to at least ~80kpc. Critical to the success of these efforts will be ensuring well-defined spectroscopic training sets that sample a broad range of stellar parameters with minimal biases. A catalog containing the training/test set and all relevant parameters within the public footprint of CFIS is available online.
- ID:
- ivo://CDS.VizieR/J/ApJS/235/5
- Title:
- EA-type eclipsing binaries observed by LAMOST
- Short Name:
- J/ApJS/235/5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- About 3196 EA-type binaries (EAs) were observed by LAMOST by 2017 June 16 and their spectral types were derived. Meanwhile, the stellar atmospheric parameters of 2020 EAs were determined. In this paper, those EAs are cataloged and their physical properties and evolutionary states are investigated. The period distribution of EAs suggests that the period limit of tidal locking for the close binaries is about 6 days. It is found that the metallicity of EAs is higher than that of EW-type binaries (EWs), indicating that EAs are generally younger than EWs and they are the progenitors of EWs. The metallicities of long-period EWs (0.4<P<1 days) are the same as those of EAs with the same periods, while their values of Log (g) are usually smaller than those of EAs. These support the evolutionary process that EAs evolve into long-period EWs through the combination of angular momentum loss (AML) via magnetic braking and case A mass transfer. For short-period EWs, their metallicities are lower than those of EAs, while their gravitational accelerations are higher. These reveal that they may be formed from cool short-period EAs through AML via magnetic braking with little mass transfer. For some EWs with high metallicities, they may be contaminated by material from the evolution of unseen neutron stars and black holes or they have third bodies that may help them to form rapidly through a short timescale of pre-contact evolution. The present investigation suggests that the modern EW populations may have formed through a combination of these mechanisms.
- ID:
- ivo://CDS.VizieR/J/ApJS/199/30
- Title:
- Effective temperature scale for KIC stars
- Short Name:
- J/ApJS/199/30
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of revised effective temperatures for stars observed in long-cadence mode in the Kepler Input Catalog (KIC). We use Sloan Digital Sky Survey (SDSS) griz filters tied to the fundamental temperature scale. Polynomials for griz color-temperature relations are presented, along with correction terms for surface gravity effects, metallicity, and statistical corrections for binary companions or blending. We compare our temperature scale to the published infrared flux method (IRFM) scale for V_T_JKs in both open clusters and the Kepler fields. We find good agreement overall, with some deviations between (J-Ks)-based temperatures from the IRFM and both SDSS filter and other diagnostic IRFM color-temperature relationships above 6000K. For field dwarfs, we find a mean shift toward hotter temperatures relative to the KIC, of order 215K, in the regime where the IRFM scale is well defined (4000K to 6500K). This change is of comparable magnitude in both color systems and in spectroscopy for stars with T_eff_ below 6000K. Systematic differences between temperature estimators appear for hotter stars, and we define corrections to put the SDSS temperatures on the IRFM scale for them. When the theoretical dependence on gravity is accounted for, we find a similar temperature scale offset between the fundamental and KIC scales for giants. We demonstrate that statistical corrections to color-based temperatures from binaries are significant. Typical errors, mostly from uncertainties in extinction, are of order 100K.
- ID:
- ivo://CDS.VizieR/J/AJ/155/68
- Title:
- Elemental abundances of KOIs in APOGEE. I.
- Short Name:
- J/AJ/155/68
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Apache Point Observatory Galactic Evolution Experiment (APOGEE) has observed ~600 transiting exoplanets and exoplanet candidates from Kepler (Kepler Objects of Interest, KOIs), most with >=18 epochs. The combined multi-epoch spectra are of high signal-to-noise ratio (typically >=100) and yield precise stellar parameters and chemical abundances. We first confirm the ability of the APOGEE abundance pipeline, ASPCAP, to derive reliable [Fe/H] and effective temperatures for FGK dwarf stars - the primary Kepler host stellar type - by comparing the ASPCAP-derived stellar parameters with those from independent high-resolution spectroscopic characterizations for 221 dwarf stars in the literature. With a sample of 282 close-in (P<100 days) KOIs observed in the APOGEE KOI goal program, we find a correlation between orbital period and host star [Fe/H] characterized by a critical period, P_crit_=8.3_-4.1_^+0.1^ days, below which small exoplanets orbit statistically more metal-enriched host stars. This effect may trace a metallicity dependence of the protoplanetary disk inner radius at the time of planet formation or may be a result of rocky planet ingestion driven by inward planetary migration. We also consider that this may trace a metallicity dependence of the dust sublimation radius, but we find no statistically significant correlation with host T_eff_ and orbital period to support such a claim.
- ID:
- ivo://CDS.VizieR/J/AJ/143/145
- Title:
- Emission-line objects from ALFALFA H{alpha} survey
- Short Name:
- J/AJ/143/145
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- During a wide-field narrowband H{alpha} imaging survey, we noted the presence of numerous isolated emission-line point sources in the data. These objects could represent ultra-low-luminosity galaxies at low-redshift (detection via H{alpha}), isolated extragalactic HII regions associated with the galaxy targeted by the original observation, or background galaxies or QSOs where strong emission lines (most often [OIII]{lambda}5007) redshift into our narrowband filter. We have carried out a systematic search for these "H{alpha} dots" in over 200 15x15arcmin fields. To date we have cataloged 61 candidate emission-line sources in roughly 11.7deg^2^. The sample has a median R magnitude of 19.5, and detects objects as faint as R=22.6. Follow-up spectroscopy reveals that ~85% of the candidates are bona fide emission-line objects, with roughly 60% of the real sources being lower-redshift objects (detection via H{alpha}) and 40% being higher-redshift objects detected via [OIII] emission or some other emission line. Here we present the results of our initial survey and follow-up spectroscopy. We use our sample to study the properties (including star-formation rates and metal abundances) of low-luminosity star-forming galaxies in the nearby universe and of low-metallicity star-forming galaxies at z~0.33.
