- ID:
- ivo://CDS.VizieR/J/ApJ/846/23
- Title:
- High-resolution spectra of 9 RGB stars in NGC6681
- Short Name:
- J/ApJ/846/23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We obtain high-resolution spectra of nine red giant branch stars in NGC 6681 and perform the first detailed abundance analysis of stars in this cluster. We confirm cluster membership for these stars based on consistent radial velocities of 214.5+/-3.7km/s and find a mean [Fe/H]=-1.63+/-0.07dex and [{alpha}/Fe]=0.42+/-0.11dex. Additionally, we confirm the existence of a Na-O anti-correlation in NGC 6681 and identify two populations of stars with unique abundance trends. With the use of HST photometry from Sarajedini+ (2007AJ....133.1658S) and Piotto+ (2015AJ....149...91P) we are able to identify these two populations as discrete sequences in the cluster CMD. Although we cannot confirm the nature of the polluter stars responsible for the abundance differences in these populations, these results do help put constraints on possible polluter candidates.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/877/104
- Title:
- High-res. spectroscopy of LAMOST Li-rich giants
- Short Name:
- J/ApJ/877/104
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The discovery of Li-rich giants has introduced a new challenge for standard stellar evolution models. To resolve this issue, the number of this type of object has been rapidly increased through the development of worldwide surveys. Taking advantage of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope survey, 44 new Li-rich giants are reported, which are confirmed with high-resolution observations. Based on the high-resolution and high signal-to-noise spectra, we derived the atmospheric parameters and elemental abundances with the spectral synthesis method. We performed a detailed analysis of their evolutionary stages, infrared excess, projected rotational velocity (vsini), and stellar population. We find that (1) the Li-rich giants concentrate at the evolutionary status of the red giant branch bump, red clump, and asymptotic giant branch; (2) three of them are fast rotators and none exhibit infrared excess. Our results imply that the origins of Li enrichment are most likely to be associated with the extra mixing in the stellar interior, and the external sources might only make a minor contribution. Moreover, various Li-rich episodes take place at different evolutionary stages.
- ID:
- ivo://CDS.VizieR/J/ApJ/805/53
- Title:
- H2O masers in W43A monitored with VLBA
- Short Name:
- J/ApJ/805/53
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the distribution patterns of H_2_O maser features in the "water fountain" source (WF) W43A and show that they are closely related to the early morphological changes in a planetary nebula (PN). Using the Very Long Baseline Array, we have detected detected H_2_O maser features in W43A in 13 epochs across >10yr. W43A is the only WF that has been observed for over a decade. We introduce a new cavity model scenario --a halo with a bipolar evacuated volume that has a partially enhanced wall-- and compare it with the "traditional" precessing jet model particularly in terms of explaining the bow-shaped distribution patterns of H_2_O maser features in the most recent epochs and their temporal evolution. Long-term observations show that the distribution patterns require more than a single jet to form. Moreover, we have identified six groups of H_2_O maser features at both the redshifted and blueshifted sides with point symmetry. The six groups are believed to correspond to periodic mass profiles in the envelope and have recorded the mass-loss history. Together with a geometric similarity to the mid-infrared morphology of W43A, the results suggest that H_2_O masers can be used to trace the inner morphology and rapid temporal changes in evolved stars, especially where the PN shaping has just started.
284. HST Hot Star Library
- ID:
- ivo://CDS.VizieR/J/A+A/615/A115
- Title:
- HST Hot Star Library
- Short Name:
- J/A+A/615/A115
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Libraries of stellar spectra find many uses in astrophysics, from photometric calibration to stellar population synthesis. We present low resolution spectra of 40 stars from 0.2 micrometers (ultraviolet) to 1.0 micrometers (near infrared) with excellent fluxing. The stars include normal O-type stars, helium-burning stars, and post-asymptotic giant branch (PAGB) stars. Spectra were obtained with the Space Telescope Imaging Spectrograph (STIS) installed in the Hubble Space Telescope (HST) using three low resolution gratings, G230LB, G430L, and G750L. Cosmic ray hits and fringing in the red were corrected. A correction for scattered light was applied, significant only for our coolest stars. Cross-correlation was used to bring the spectra to a common, final, zero velocity wavelength scale. Finally, synthetic stellar spectra were used to estimate line of sight dust extinction to each star, and a five-parameter dust extinction model was fit, or a one-parameter fit in the case of low extinction. These spectra dovetail with the similar Next Generation Stellar Library (NGSL) spectra, extending the NGSL's coverage of stellar parameters, and extending to helium burning stars and stars that do not fuse. The fitted dust extinction model showed considerable variation from star to star, indicating variations in dust properties for different lines of sight. Interstellar absorption lines are present in most stars, notably MgII.
- ID:
- ivo://CDS.VizieR/J/MNRAS/452/910
- Title:
- IC 1613 asymptotic giant branch variables
- Short Name:
- J/MNRAS/452/910
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- JHKs photometry is presented from a 3-yr survey of the central regions of the Local Group dwarf irregular galaxy IC 1613. The morphologies of the colour-magnitude and colour-colour diagrams are discussed with particular reference to the supergiants and M- and C-type asymptotic giant branch (AGB) stars. Mean JHKs magnitudes, amplitudes and periods are given for five O-rich and nine C-rich Mira variables for which bolometric magnitudes are also estimated. A distance of 750kpc ((m-M)0=24.37+/-0.08mag) is derived for IC 1613 by fitting a period-luminosity (PL) relation to the C-rich Miras. This is in agreement with values from the literature. The AGB stars exhibit a range of ages. A comparison with theoretical isochrones suggests that four luminous O-rich Miras are as young as 2x10^8^yr. One of these has a lithium absorption line in its spectrum, demonstrating that it is undergoing hot bottom burning (HBB). This supports the idea that HBB is the cause of the high luminosity of these AGB stars, which puts them above the fundamental PL relation. Further studies of similar stars, selected from their positions in the PL diagram, could provide insight into HBB. A much fainter, presumed O-rich, Mira is similar to those found in Galactic globular clusters. The C Miras are of intermediate age. The O-rich variables are not all recognized as O-rich, or even as AGB stars, on the basis of their J-Ks colour. It is important to appreciate this when using near-infrared surveys to classify AGB stars in more distant galaxies.
- ID:
- ivo://CDS.VizieR/J/A+AS/107/39
- Title:
- IC 2714 UBV photometry
- Short Name:
- J/A+AS/107/39
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- UBV photoelectric photometry for 204 stars in the field of the southern open cluster IC 2714 supplemented by DDO and Washington photometry and Coravel radial velocities of 14 probable red giants, are presented. The analysis of the photometric and kinematical data yielded 132 probable members and 13 possible members. IC 2714 contains one variable star and 11 red giant members, one of them being a spectroscopic binary. Two red giants are either binaries or non-members. The reddening across the cluster is slightly variable, the mean value is E(B-V)=0.36. The cluster distance-modulus is 11.68, corresponding to a distance of 1320(+/-120)pc and the mean radial velocity is -14.1+/-0.3km/s. The age, determined by fitting isochrones with core overshooting turned out to be log(t)=8.5, corresponding to 3.2 10^8 yr. A metal abundance [Fe/H]=-0.12+/-0.09 relative to the Sun and other fundamental parameters are determined. The luminosity function of the bright members of IC 2714 in good agreement with that determined by Taff (1974AJ.....79.1280T). For a description of the UBV, DDO and Washington photometric system, see e.g. <GCPD/01>, <GCPD/12> and <GCPD/45>
- ID:
- ivo://CDS.VizieR/J/A+A/597/A25
- Title:
- IK Tau millimeter IRAM-30m line survey
- Short Name:
- J/A+A/597/A25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We aim to investigate the physical and chemical properties of the molecular envelope of the oxygen-rich AGB star IK Tau. We carried out a millimeter wavelength line survey between ~79 and 356GHz with the IRAM-30m telescope. We analysed the molecular lines detected in IK Tau using the population diagram technique to derive rotational temperatures and column densities. We conducted a radiative transfer analysis of the SO_2_ lines, which also helped us to verify the validity of the approximated method of the population diagram for the rest of the molecules.
- ID:
- ivo://CDS.VizieR/J/A+A/645/A124
- Title:
- Inclinations for RGBs from Kepler asteroseismology
- Short Name:
- J/A+A/645/A124
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Measuring stellar inclinations is fundamental to understand planetary formation and dynamics as well as physical conditions during star formation. Oscillation spectra of red giant stars exhibit mixed modes that have both a gravity component from the radiative interior and a pressure component from the convective envelope. Gravity-dominated (g-m) mixed modes split by rotation are well separated inside frequency spectra, making possible accurate measurements of stellar inclinations. This work aims at developing an automated and general approach to measure stellar inclinations, that can be applied to any solar-type pulsator for which oscillation modes are identified, and at validating it using red giant branch stars observed by Kepler. The stellar inclination impacts the visibility of oscillation modes with azimuthal orders m=(-1,0,+1). We use the mean height-to-background ratio of dipole mixed modes with different azimuthal orders to measure stellar inclinations. The underlying statistical distribution of inclinations is recovered in an unbiased way using a probability density function for the stellar inclination angle. We derive stellar inclination measurements for 1140 stars on the red giant branch, for which Gehan et al. (2018A&A...616A..24G, Cat. J/A+A/616/A24) have identified the azimuthal order of dipole g-m mixed modes. Raw measured inclinations exhibit strong deviation with respect to isotropy which is expected for random inclinations over the sky. When taking uncertainties into account, the reconstructed distribution of inclinations actually follows the expected isotropic distribution of the rotational axis. This work highlights the biases that affect inclination measurements and provides the way to infer their underlying statistical distribution. When the star is seen either pole-on or equator-on, measurements are challenging and result in a biased distribution. Correcting biases that appear at the low- and high inclination regimes allows us to recover the underlying inclination distribution.
- ID:
- ivo://CDS.VizieR/J/A+A/523/A17
- Title:
- Individual stars in Fornax dSph center
- Short Name:
- J/A+A/523/A17
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- For the first time we show the detailed, late-stage, chemical evolution history of a small nearby dwarf spheroidal galaxy in the Local Group. We present the results of a high-resolution (R~20000, {lambda}=5340-5620; 6120-6701) FLAMES/GIRAFFE abundance study at ESO/VLT of 81 photometrically selected, red giant branch stars in the central 25' of the Fornax dwarf spheroidal galaxy. We also carried out a detailed comparison of the effects of recent developments in abundance analysis (e.g., spherical models vs. plane-parallel) and the automation that is required to efficiently deal with such large data sets. We present abundances of alpha-elements (Mg, Si, Ca, and Ti), iron-peak elements (Fe, Ni, and Cr), and heavy elements (Y, Ba, La, Nd, and Eu).
- ID:
- ivo://CDS.VizieR/J/AJ/104/1349
- Title:
- Infrared-luminous giants in M32
- Short Name:
- J/AJ/104/1349
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A previously unknown population of very luminous, red, asymptotic-giant-branch stars has been identified as a result of near-infrared (JHK) imaging in the dwarf elliptical galaxy M32. Situated above the tip of the normal first red giant branch, these stars are intrinsically brighter than the most luminous normal giants in old Galactic globular clusters by approximately 2 bolometric magnitudes. Moreover, they are a full bolometric magnitude brighter than the brightest giants observed in our own Galactic bulge. Several possible explanations for this population are examined, including old long-period variables, binary mergers, supermetallicity, and intermediate-age stars. It is suggested that the simplest explanation at present, is that M32 had a star formation episode less than about 5 billion years ago. These stars would then be the evolved extended asymptotic giant branch population resulting from that event (similar to those stars observed in the intermediate-age clusters in the Magellanic Clouds). This population may be similar to that in the M31 bulge, recently observed by Rich and Mould. The detection of a young component in M32 is of particular interest because historically, M32 has been a fiducial galaxy for population synthesis techniques. An understanding of M32 remains crucial for our understanding of distant and more luminous elliptical galaxies.
