- ID:
- ivo://CDS.VizieR/J/ApJ/830/93
- Title:
- Abundances of the Ret II brightest red giant members
- Short Name:
- J/ApJ/830/93
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present chemical abundances derived from high-resolution Magellan/Magellan Inamori Kyocera Echelle spectra of the nine brightest known red giant members of the ultra-faint dwarf galaxy Reticulum II (Ret II). These stars span the full metallicity range of Ret II (-3.5<[Fe/H]< -2). Seven of the nine stars have extremely high levels of r-process material ([Eu/Fe]~1.7), in contrast to the extremely low neutron-capture element abundances found in every other ultra-faint dwarf galaxy studied to date. The other two stars are the most metal-poor stars in the system ([Fe/H]< -3), and they have neutron-capture element abundance limits similar to those in other ultra-faint dwarf galaxies. We confirm that the relative abundances of Sr, Y, and Zr in these stars are similar to those found in r-process halo stars, but they are ~0.5dex lower than the solar r-process pattern. If the universal r-process pattern extends to those elements, the stars in Ret II display the least contaminated known r-process pattern. The abundances of lighter elements up to the iron peak are otherwise similar to abundances of stars in the halo and in other ultra-faint dwarf galaxies. However, the scatter in abundance ratios is large enough to suggest that inhomogeneous metal mixing is required to explain the chemical evolution of this galaxy. The presence of low amounts of neutron-capture elements in other ultra-faint dwarf galaxies may imply the existence of additional r-process sites besides the source of r-process elements in Ret II. Galaxies like Ret II may be the original birth sites of r-process enhanced stars now found in the halo.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/819/103
- Title:
- Abundances of two very metal-poor stars
- Short Name:
- J/ApJ/819/103
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- From high resolution (R~=45000), high signal-to-noise ratio (S/N>400) spectra gathered with the Immersion Grating Infrared Spectrograph (IGRINS) in the H and K photometric bands, we have derived elemental abundances of two bright, well-known metal-poor halo stars: the red giant HD 122563 and the subgiant HD 140283. Since these stars have metallicities approaching [Fe/H]=-3, their absorption features are generally very weak. Neutral-species lines of Mg, Si, S and Ca are detectable, as well as those of the light odd-Z elements Na and Al. The derived IR-based abundances agree with those obtained from optical-wavelength spectra. For Mg and Si the abundances from the infrared transitions are improvements to those derived from shorter wavelength data. Many useful OH and CO lines can be detected in the IGRINS HD 122563 spectrum, from which derived O and C abundances are consistent to those obtained from the traditional [OI] and CH features. IGRINS high resolutions H- and K-band spectroscopy offers promising ways to determine more reliable abundances for additional metal-poor stars whose optical features are either not detectable, or too weak, or are based on lines with analytical difficulties.
- 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/857/27
- Title:
- A catalog of post-starburst QSOs from SDSS-DR7Q
- Short Name:
- J/ApJ/857/27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of nearby (z<=0.5) quasars with significant features of post-starburst stellar populations in their optical spectra: so-called post-starburst quasars, or PSQs. After carefully decomposing spectra from the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) Quasar Catalog into quasar and host-galaxy components, we derive a sample of 208 PSQs. Their host-galaxy components have strong H{delta} absorption (EW>=6{AA}) indicating a significant contribution of an intermediate-aged stellar population formed in a burst of star formation within the past 1Gyr, which makes them potentially useful for studying the co-evolution of supermassive black holes and their host galaxies.
- ID:
- ivo://CDS.VizieR/J/A+A/561/A2
- Title:
- 36 accreting YSOs emission lines
- Short Name:
- J/A+A/561/A2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present VLT/X-shooter observations of a sample of 36 accreting low-mass stellar and substellar objects (YSOs) in the Lupus star-forming region, spanning a range in mass from ~0.03 to ~1.2M_{sun}_, but mostly with 0.1M_{sun}_<M*<0.5M_{sun}_. Our aim is twofold: firstly, to analyse the relationship between excess-continuum and line emission accretion diagnostics, and, secondly, to investigate the accretion properties in terms of the physical properties of the central object. The accretion luminosity (L_acc_), and in turn the accretion rate (dM/dt_acc_), was derived by modelling the excess emission from the UV to the near-infrared as the continuum emission of a slab of hydrogen. We computed the flux and luminosity (L_line_) of many emission lines of H, He, and CaII, observed simultaneously in the range from ~330nm to 2500nm.
- ID:
- ivo://CDS.VizieR/J/A+A/579/A66
- Title:
- Accretion in {rho}-Ophiucus
- Short Name:
- J/A+A/579/A66
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new VLT/X-Shooter optical and near-infrared spectra of a sample of 17 candidate young low-mass stars and brown dwarfs located in the {rho}-Ophiucus cluster. We derived the spectral type and extinction for all the targets, and then we determined their physical parameters. All the objects but one have M_*_<~0.6M_{sun}_, and eight have mass below or close to the hydrogen-burning limit. Using the intensity of various permitted emission lines present in their spectra, we determined the accretion luminosity and mass accretion rates ({dot}(M)_acc_) for all the objects. When compared with previous works targeting the same sample, we find that, in general, these objects are not as strongly accreting as previously reported, and we suggest that the reason is our more accurate estimate of the photospheric parameters. We also compare our findings with recent works in other slightly older star-forming regions, such as Lupus, to investigate possible differences in the accretion properties, but we find that the accretion properties for our targets have the same dependence on the stellar and substellar parameters as in the other regions. This leads us to conclude that we do not find evidence for a different dependence of {dot}(M)_acc_ with M_*_ when comparing low-mass stars and brown dwarfs. Moreover, we find a similar small (<~1dex) scatter in the {dot}(M)_acc_-M_*_ relation as in some of our recent works in other star-forming regions, and no significant differences in {dot}(M)_acc_ due to different ages or properties of the regions. The latter result suffers, however, from low statistics and sample selection biases in the current studies. The small scatter in the {dot}(M)_acc_-M_*_ correlation confirms that mass accretion rate measurements in the literature based on uncertain photospheric parameters and single accretion indicators, such as the H{alpha} width, can lead to a scatter that is unphysically large. Our studies show that only broadband spectroscopic surveys coupled with a detailed analysis of the photospheric and accretion properties allows us to properly study the evolution of disk accretion rates in star-forming regions.
- ID:
- ivo://CDS.VizieR/J/ApJ/769/21
- Title:
- Accretion luminosities of young stars from Pf{beta}
- Short Name:
- J/ApJ/769/21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work, we introduce the use of HI Pfund {beta} (Pf{beta}; 4.6538{mu}m) as a tracer of mass accretion from protoplanetary disks onto young stars. Pf{beta} was serendipitously observed in NIRSPEC and CRIRES surveys of CO fundamental emission, amounting to a sample size of 120 young stars with detected Pf{beta} emission. Using a subsample of disks with previously measured accretion luminosities, we show that Pf{beta} line luminosity is well correlated with accretion luminosity over a range of at least three orders of magnitude. We use this correlation to derive accretion luminosities for all 120 targets, 65 of which are previously unreported in the literature. The conversion from accretion luminosity to accretion rate is limited by the availability of stellar mass and radius measurements; nevertheless, we also report accretion rates for 67 targets, 16 previously unmeasured. Our large sample size and our ability to probe high extinction values allow for relatively unbiased comparisons between different types of disks.
- ID:
- ivo://CDS.VizieR/J/A+A/586/A47
- Title:
- Accretion process in NGC 2264
- Short Name:
- J/A+A/586/A47
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC 2264 is a young stellar cluster (~3Myr) with hundreds of low-mass accreting stars that allow a detailed analysis of the accretion process taking place in the pre-main sequence. Our goal is to relate the photometric and spectroscopic variability of classical T Tauri stars to the physical processes acting in the stellar and circumstellar environment, within a few stellar radii from the star. NGC 2264 was the target of a multiwavelength observational campaign with CoRoT, MOST, Spitzer, and Chandra satellites and photometric and spectroscopic observations from the ground. We classified the CoRoT light curves of accreting systems according to their morphology and compared our classification to several accretion diagnostics and disk parameters.
- ID:
- ivo://CDS.VizieR/J/ApJ/871/193
- Title:
- A combined Chandra & LAMOST study of stellar activity
- Short Name:
- J/ApJ/871/193
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We probed stellar X-ray activity over a wide range of stellar parameters, using Chandra and Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) data. We measured the X-ray-to-bolometric luminosity ratio (R_X_=L_X_/L_bol_) for 484 main-sequence stars and found a bimodal distribution for G and K types. We interpret this bimodality as evidence of two subpopulations with different coronal temperatures, which are caused by different coronal heating rates. Using the metallicity and velocity information, we find that both of the subpopulations are mostly located in the thin disk. We find no trend of R_X_ with stellar age for stars older than ~4Gyr; there is a trough in the R_X_ versus age distribution, with the lowest range of R_X_ appearing at ages around 2Gyr. We then examined the correlation between R_X_ and R_H{alpha}_ (proxy of chromospheric activity): we find that the two quantities are well correlated, as found in many earlier studies. Finally, we selected a sample of 12 stars with X-ray flares and studied the light-curve morphology of the flares. The variety of flare profiles and timescales observed in our sample suggests the contribution of different processes of energy release.
