- ID:
- ivo://CDS.VizieR/J/ApJ/723/1632
- Title:
- Abundance spreads in Bootes I and Segue 1
- Short Name:
- J/ApJ/723/1632
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an AAOmega spectroscopic study of red giants in the ultra-faint dwarf galaxy Bootes I (M_V_~-6) and the Segue 1 system (M_V_~-1.5), either an extremely low luminosity dwarf galaxy or an unusually extended globular cluster. Both Bootes I and Segue 1 have significant abundance dispersions in iron and carbon. Bootes I has a mean abundance of [Fe/H]=-2.55+/-0.11 with an [Fe/H] dispersion of {sigma}=0.37+/-0.08, and abundance spreads of {Delta}[Fe/H]=1.7 and {Delta}[C/H]=1.5. Segue 1 has a mean of [Fe/H]=-2.7+/-0.4 with [Fe/H] dispersion of {sigma}=0.7+/-0.3, and abundances spreads of {Delta}[Fe/H]=1.6 and {Delta}[C/H]=1.2. Moreover, Segue 1 has a radial-velocity member at four half-light radii that is extremely metal-poor and carbon-rich, with [Fe/H]=-3.5, and [C/Fe]=+2.3. Modulo an unlikely non-member contamination, the [Fe/H] abundance dispersion confirms Segue 1 as the least-luminous ultra-faint dwarf galaxy known.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/538/A100
- Title:
- Abundances red giants in Carina dSph
- Short Name:
- J/A+A/538/A100
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The ages of individual Red Giant Branch stars can range from 1Gyr old to the age of the Universe, and it is believed that the abundances of most chemical elements in their photospheres remain unchanged with time (those that are not affected by the first dredge-up). This means that they trace the interstellar medium in the galaxy at the time the star formed, and hence the chemical enrichment history of the galaxy. Colour-Magnitude Diagram analysis has shown the Carina dwarf spheroidal to have had an unusually episodic star formation history and this is expected to be reflected in the abundances of different chemical elements.
- ID:
- ivo://CDS.VizieR/J/ApJ/836/168
- Title:
- Abundances & RVs for stars near (or in) NGC6273
- Short Name:
- J/ApJ/836/168
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent observations have shown that a growing number of the most massive Galactic globular clusters contain multiple populations of stars with different [Fe/H] and neutron-capture element abundances. NGC 6273 has only recently been recognized as a member of this "iron-complex" cluster class, and we provide here a chemical and kinematic analysis of >300 red giant branch and asymptotic giant branch member stars using high-resolution spectra obtained with the Magellan-M2FS and VLT-FLAMES instruments. Multiple lines of evidence indicate that NGC 6273 possesses an intrinsic metallicity spread that ranges from about [Fe/H]=-2 to -1 dex, and may include at least three populations with different [Fe/H] values. The three populations identified here contain separate first (Na/Al-poor) and second (Na/Al-rich) generation stars, but a Mg-Al anti-correlation may only be present in stars with [Fe/H]>~-1.65. The strong correlation between [La/Eu] and [Fe/H] suggests that the s-process must have dominated the heavy element enrichment at higher metallicities. A small group of stars with low [{alpha}/Fe] is identified and may have been accreted from a former surrounding field star population. The cluster's large abundance variations are coupled with a complex, extended, and multimodal blue horizontal branch (HB). The HB morphology and chemical abundances suggest that NGC 6273 may have an origin that is similar to {omega} Cen and M54.
- ID:
- ivo://CDS.VizieR/J/ApJ/848/68
- Title:
- Abundances & RVs of stable and Blazhko RRc stars
- Short Name:
- J/ApJ/848/68
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyzed series of spectra obtained for 12 stable RRc stars observed with the echelle spectrograph of the du Pont telescope at Las Campanas Observatory and we analyzed the spectra of RRc Blazhko stars discussed by Govea+ (2014, J/ApJ/782/59). We derived model atmosphere parameters, [Fe/H] metallicities, and [X/Fe] abundance ratios for 12 species of 9 elements. We co-added all spectra obtained during the pulsation cycles to increase signal to noise and demonstrate that these spectra give results superior to those obtained by co-addition in small phase intervals. The RRc abundances are in good agreement with those derived for the RRab stars of Chadid+ (2017ApJ...835..187C). We used radial velocity (RV) measurements of metal lines and H{alpha} to construct variations of velocity with phase, and center-of-mass velocities. We used these to construct RV templates for use in low- to medium-resolution RV surveys of RRc stars. Additionally, we calculated primary accelerations, radius variations, and metal and H{alpha} velocity amplitudes, which we display as regressions against primary acceleration. We employ these results to compare the atmosphere structures of metal-poor RRc stars with their RRab counterparts. Finally, we use the RV data for our Blazhko stars and the Blazhko periods of Szczygiel & Fabrycky (2007, J/MNRAS/377/1263) to falsify the Blazhko oblique rotator hypothesis.
- ID:
- ivo://CDS.VizieR/J/A+A/554/A106
- Title:
- Abundance study of LMC post-AGB stars
- Short Name:
- J/A+A/554/A106
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The photospheric abundances of evolved solar-type stars of different metallicities serve as probes into stellar evolution theory. Stellar photospheres of post-asymptotic giant branch (post-AGB) stars bear witness to the internal chemical enrichment processes, integrated over their entire stellar evolution. Here we study post-AGB stars in the Large Magellanic Cloud (LMC). With their known distances, these rare objects are ideal tracers of AGB nucleosynthesis and dredge-up phenomena.
- ID:
- ivo://CDS.VizieR/J/A+A/583/A56
- Title:
- Abundance study of two LMC post-AGB stars
- Short Name:
- J/A+A/583/A56
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper is part of a larger project in which we systematically study the chemical abundances of extra-galactic post-asymptotic giant branch (post-AGB) stars. The aim of our programme is to derive chemical abundances of stars covering a large range in luminosity and metallicity with the ultimate goal of testing, constraining, and improving our knowledge of the poorly understood AGB phase, especially the third dredge-up mixing processes and associated s-process nucleosynthesis. Post-AGB photospheres are dominated by atomic lines and indicate the effects of internal chemical enrichment processes over the entire stellar lifetime. In this paper, we study two carefully selected post-AGB stars: J051213.81-693537.1 and J051848.86-700246.9 in the Large Magellanic Cloud (LMC). Both objects show signs of s-process enhancement. The combination of favourable atmospheric parameters for detailed abundance studies and their known distances (and hence luminosities and initial masses) make these objects ideal probes of the AGB third dredge-up and s-process nucleosynthesis in that they provide observational constraints for theoretical AGB models.
- ID:
- ivo://CDS.VizieR/J/AJ/154/155
- Title:
- Abundance variations in the outer halo GC NGC 6229
- Short Name:
- J/AJ/154/155
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC 6229 is a relatively massive outer halo globular cluster that is primarily known for exhibiting a peculiar bimodal horizontal branch morphology. Given the paucity of spectroscopic data on this cluster, we present a detailed chemical composition analysis of 11 red giant branch members based on high resolution (R~38000), high S/N (>100) spectra obtained with the MMT-Hectochelle instrument. We find the cluster to have a mean heliocentric radial velocity of -138.1_-1.0_^+1.0^ km/s, a small dispersion of 3.8_-0.7_^+1.0^ km/s, and a relatively low (M/L_V_)_{sun}_=0.82_-0.28_^+0.49^. The cluster is moderately metal-poor with <[Fe/H]>=-1.13 dex and a modest dispersion of 0.06 dex. However, 18% (2/11) of the stars in our sample have strongly enhanced [La,Nd/Fe] ratios that are correlated with a small (~0.05 dex) increase in [Fe/H]. NGC 6229 shares several chemical signatures with M75, NGC 1851, and the intermediate metallicity populations of {omega} Cen, which lead us to conclude that NGC 6229 is a lower mass iron-complex cluster. The light elements exhibit the classical (anti-)correlations that extend up to Si, but the cluster possesses a large gap in the O-Na plane that separates first and second generation stars. NGC 6229 also has unusually low [Na,Al/Fe] abundances that are consistent with an accretion origin. A comparison with M54 and other Sagittarius clusters suggests that NGC 6229 could also be the remnant core of a former dwarf spheroidal galaxy.
- ID:
- ivo://CDS.VizieR/J/A+A/631/A113
- Title:
- Abund. of disk & bulge giants: Zr, La, Ce, Eu
- Short Name:
- J/A+A/631/A113
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Observations of the Galactic bulge suggest that the disk formed through secular evolution rather than gas dissipation and/or mergers, as previously believed. This would imply very similar chemistry in the disk and bulge. Some elements, such as the {alpha}-elements, are well studied in the bulge, but others like the neutron-capture elements are much less well explored. Stellar mass and metallicity are factors that affect the neutron-capture process. Due to this, the enrichment of the ISM and the abundance of neutron-capture elements vary with time, making them suitable probes for Galactic chemical evolution. In this work, we make a differential comparison of neutron-capture element abundances determined in the local disk(s) and the bulge, focusing on minimising possible systematic effects in the analysis, with the aim of finding possible differences/similarities between the populations. Abundances are determined for Zr, La, Ce, and Eu in 45 bulge giants and 291 local disk giants, from high-resolution optical spectra. The abundances are determined by fitting synthetic spectra using the SME-code. The disk sample is separated into thin- and thick-disk components using a combination of abundances and kinematics. We find flat Zr, La, and Ce trends in the bulge, with a ~0.1dex higher La abundance compared with the disk, possibly indicating a higher s-process contribution for La in the bulge. [Eu/Fe] decreases with increasing [Fe/H], with a plateau at around [Fe/H]~-0.4, pointing at similar enrichment to {alpha}-elements in all populations. We find that the r-process dominated the neutron-capture production at early times both in the disks and bulge. Further, [La/Eu] ratios for the bulge are systematically higher than for the thick disk, pointing to either a) a different amount of SN II or b) a different contribution of the s-process in the two populations. Considering [(La+Ce)/Zr], the bulge and the thick disk follow each other closely, suggesting a similar ratio of high-to-low-mass asymptotic giant branch stars.
- ID:
- ivo://CDS.VizieR/J/A+A/621/A133
- Title:
- ABYSS HUDF WFC3 IR mosaics
- Short Name:
- J/A+A/621/A133
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Hubble Ultra Deep field (HUDF) is the deepest region ever observed with the Hubble Space Telescope. With the main objective of unveiling the nature of galaxies up to z~7-8, the observing and reduction strategy have focused on the properties of small and unresolved objects, rather than the outskirts of the largest objects, which are usually over-subtracted. We aim to create a new set of WFC3 IR mosaics of the HUDF using novel techniques to preserve the properties of the low surface brightness regions. We created ABYSS a pipeline that optimises the estimate and modelling of low-level systematic effects to obtain a robust background subtraction. We have improved four key points in the reduction: 1) creation of new absolute sky flat fields, 2) extended persistence models, 3) dedicated sky background subtraction and 4) robust co-adding. The new mosaics successfully recover the low surface brightness structure removed on the previous HUDF published reductions. The amount of light recovered with a mean surface brightness dimmer than mu=26mag/arcsec^2^ is equivalent to a m=19 mag source when compared to the XDF and a m=20mag compared to the HUDF12. We present a set of techniques to reduce ultra-deep images (mu>32.5mag/arcsec^2^, 3 sigma in 10x10 arcsec boxes), that successfully allow to detect the low surface brightness structure of extended sources on ultra deep surveys. The developed procedures are applicable to HST, JWST, EUCLID and many other space and ground-based observatories. We made the final ABYSS WFC3 IR HUDF mosaics publicly available at http://www.iac.es/proyecto/abyss/.
- ID:
- ivo://CDS.VizieR/J/A+A/651/A93
- Title:
- A candidate super-Earth orbiting GJ 9689
- Short Name:
- J/A+A/651/A93
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- It is now well-established that small, rocky planets are common around low-mass stars. However, the detection of such planets is challenged by the short-term activity of the host stars. The HArps-N red Dwarf Exoplanet Survey (HADES) program is a long-term project at the Telescopio Nazionale Galileo aimed at the monitoring of nearby, early-type, M dwarfs, using the HARPS-N spectrograph to search for small, rocky planets. A total of 174 HARPS-N spectroscopic observations of the M0.5V-type star GJ 9689 taken over the past seven years have been analysed. We combined these data with photometric measurements to disentangle signals related to the stellar activity of the star from possible Keplerian signals in the radial velocity data. We run an MCMC analysis, applying Gaussian Process regression techniques to model the signals present in the data. We identify two periodic signals in the radial velocity time series, with periods of 18.27d, and 39.31d. The analysis of the activity indexes, photometric data, and wavelength dependency of the signals reveals that the 39.31d signal corresponds to the stellar rotation period. On the other hand, the 18.27d signal shows no relation to any activity proxy or the first harmonic of the rotation period. We, therefore, identify it as a genuine Keplerian signal. The best-fit model describing the newly found planet, GJ 9689 b, corresponds to an orbital period P_b_=18.27+/-0.01d, and a minimum mass M_P_sini=9.65+/-1.41M_{sun}_.
