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24641. 7 year Swift-XRT point source catalog (1SWXRT)
ID:
ivo://CDS.VizieR/J/A+A/551/A142
Title:
7 year Swift-XRT point source catalog (1SWXRT)
Short Name:
J/A+A/551/A142
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Swift satellite is a multi-wavelength observatory specifically designed for gamma-ray burst (GRB) astronomy that is operational since 2004. Swift is also a very flexible multi-purpose facility that supports a wide range of scientific fields such as active galactic nuclei, supernovae, cataclysmic variables, Galactic transients, active stars and comets. The Swift X-ray Telescope (XRT) has collected more than 150Ms of observations in its first seven years of operations. The purpose of this work is to present to the scientific community the list of all the X-ray point sources detected in XRT imaging data taken in photon counting mode during the first seven years of Swift operations. All these point-like sources, excluding the Gamma-Ray Bursts (GRB), will be stored in a catalog publicly available (1SWXRT). We consider all the XRT observations with exposure time longer than 500 s taken in the period 2005-2011. Data were reduced and analyzed with standard techniques and a list of detected sources for each observation was produced. A careful visual inspection was performed to remove extended, spurious and piled-up sources. Finally, positions, count rates, fluxes and the corresponding uncertainties were computed.
24642. Yee et al. 2017
ID:
ivo://svo.cab/cat/yee2017
Title:
Yee et al. 2017
Short Name:
FGKM-Yee2017
Date:
11 Jun 2020 09:42:56
Publisher:
SVO/CAB
Description:
Precision Stellar Characterization of FGKM Stars using an Empirical Spectral Library
24643. Yellow and red supergiants in the LMC
ID:
ivo://CDS.VizieR/J/ApJ/749/177
Title:
Yellow and red supergiants in the LMC
Short Name:
J/ApJ/749/177
Date:
21 Oct 2021
Publisher:
CDS
Description:
Due to their transitionary nature, yellow supergiants (YSGs) provide a critical challenge for evolutionary modeling. Previous studies within M31 and the Small Magellanic Cloud show that the Geneva evolutionary models do a poor job at predicting the lifetimes of these short-lived stars. Here, we extend this study to the Large Magellanic Cloud (LMC) while also investigating the galaxy's red supergiant (RSG) content. This task is complicated by contamination by Galactic foreground stars that color and magnitude criteria alone cannot weed out. Therefore, we use proper-motions and the LMC's large systemic radial velocity (~278km/s) to separate out these foreground dwarfs. After observing nearly 2000 stars, we identified 317 probable YSGs, 6 possible YSGs, and 505 probable RSGs. Foreground contamination of our YSG sample was ~80%, while that of the RSG sample was only 3%. By placing the YSGs on the Hertzsprung-Russell diagram and comparing them against the evolutionary tracks, we find that new Geneva evolutionary models do an exemplary job at predicting both the locations and the lifetimes of these transitory objects.
24644. Yellowballs in Milky Way project
ID:
ivo://CDS.VizieR/J/ApJ/799/153
Title:
Yellowballs in Milky Way project
Short Name:
J/ApJ/799/153
Date:
21 Oct 2021
Publisher:
CDS
Description:
Yellowballs are a collection of approximately 900 compact, infrared sources identified and named by volunteers participating in the Milky Way Project (MWP), a citizen science project that uses GLIMPSE/MIPSGAL images from Spitzer to explore topics related to Galactic star formation. In this paper, through a combination of catalog cross-matching and infrared color analysis, we show that yellowballs are a mix of compact star-forming regions, including ultra-compact and compact HII regions, as well as analogous regions for less massive B-type stars. The resulting MWP yellowball catalog provides a useful complement to the Red MSX Source survey. It similarly highlights regions of massive star formation, but the selection of objects purely on the basis of their infrared morphology and color in Spitzer images identifies a signature of compact star-forming regions shared across a broad range of luminosities and, by inference, masses. We discuss the origin of their striking mid-infrared appearance and suggest that future studies of the yellowball sample will improve our understanding of how massive and intermediate-mass star-forming regions transition from compact to more extended bubble-like structures.
24645. Yellow supergiants in M31
ID:
ivo://CDS.VizieR/J/ApJ/703/441
Title:
Yellow supergiants in M31
Short Name:
J/ApJ/703/441
Date:
21 Oct 2021
Publisher:
CDS
Description:
The yellow supergiant (F- and G-type) content of nearby galaxies can provide a critical test of stellar evolution theory, bridging the gap between the hot, massive stars and the cool red supergiants. But, this region of the color-magnitude diagram is dominated by foreground contamination, requiring membership to somehow be determined. Fortunately, the large negative systemic velocity of M31, coupled to its high rotation rate, provides the means for separating the contaminating foreground dwarfs from the bona fide yellow supergiants within M31. We obtained radial velocities of ~2900 individual targets within the correct color-magnitude range corresponding to masses of 12M_{sun}_ and higher. A comparison of these velocities to those expected from M31's rotation curve reveals 54 rank-1 (near certain) and 66 rank-2 (probable) yellow supergiant members, indicating a foreground contamination >=96%. We expect some modest contamination from Milky Way halo giants among the remainder, particularly for the rank-2 candidates, and indeed follow-up spectroscopy of a small sample eliminates four rank 2's while confirming five others.
24646. Yellow supergiants in the SMC
ID:
ivo://CDS.VizieR/J/ApJ/719/1784
Title:
Yellow supergiants in the SMC
Short Name:
J/ApJ/719/1784
Date:
21 Oct 2021
Publisher:
CDS
Description:
The yellow supergiant content of nearby galaxies provides a critical test of massive star evolutionary theory. While these stars are the brightest in a galaxy, they are difficult to identify because a large number of foreground Milky Way stars have similar colors and magnitudes. We previously conducted a census of yellow supergiants within M31 and found that the evolutionary tracks predict a yellow supergiant duration an order of magnitude longer than we observed. Here we turn our attention to the Small Magellanic Cloud (SMC), where the metallicity is 10x lower than that of M31, which is important as metallicity strongly affects massive star evolution. The SMC's large radial velocity (~160km/s) allows us to separate members from foreground stars. Observations of ~500 candidates yielded 176 near-certain SMC supergiants, 16 possible SMC supergiants, along with 306 foreground stars, and provide good relative numbers of yellow supergiants down to 12M_{sun}_. Of the 176 near-certain SMC supergiants, the kinematics predicted by the Besancon model of the Milky Way suggest a foreground contamination of <=4%. After placing the SMC supergiants on the Hertzsprung-Russell diagram (HRD) and comparing our results to the Geneva evolutionary tracks, we find results similar to those of the M31 study: while the locations of the stars on the HRD match the locations of evolutionary tracks well, the models overpredict the yellow supergiant lifetime by a factor of 10. Uncertainties about the mass-loss rates on the main sequence thus cannot be the primary problem with the models.
24647. Yields for Z=1e-5 intermediate-mass stars
ID:
ivo://CDS.VizieR/J/A+A/645/A10
Title:
Yields for Z=1e-5 intermediate-mass stars
Short Name:
J/A+A/645/A10
Date:
21 Oct 2021
Publisher:
CDS
Description:
Observed abundances of extremely metal-poor (EMP) stars in the Halo hold clues for the understanding of the ancient universe. Interpreting these clues requires theoretical stellar models at the low-Z regime. We provide the nucleosynthetic yields of intermediate-mass Z=10^-5^ stars between 3 and 7.5M_{sun}_, and quantify the effects of the uncertain wind rates. We expect these yields can be eventually used to assess the contribution to the chemical inventory of the early universe, and to help interpret abundances of selected C-enhanced EMP stars. By comparing our models and other existing in the literature, we explore evolutionary and nucleosynthetic trends with wind prescriptions and with initial metallicity. We compare our results to observations of CEMP-s stars belonging to the Halo. The yields of intermediate-mass EMP stars reflect the effects of very deep second dredge-up (for the most massive models), superimposed with the combined signatures of hot-bottom burning and third dredge-up. We confirm the reported trend that models with initial metallicity Zini<=0.001 give positive yields of ^12^C, ^15^N, ^16^O, and ^26^Mg. The ^20^Ne, ^21^Ne, and ^24^Mg yields, which were reported to be negative at Zini=0.0001, become positive for Z=10^-5^. The results using two different prescriptions for mass-loss rates differ widely in terms of the duration of the thermally-pulsing (Super) AGB phase, overall efficiency of the third dredge-up episode, and nucleosynthetic yields. The most efficient of the standard wind rates frequently used in the literature seems to favour agreement between our yield results and observational data. Regardless of the wind prescription, all our models become N-enhanced EMP stars.
24648. Yields from extremely metal-poor stars
ID:
ivo://CDS.VizieR/J/A+A/490/769
Title:
Yields from extremely metal-poor stars
Short Name:
J/A+A/490/769
Date:
21 Oct 2021
Publisher:
CDS
Description:
The growing body of spectral observations of the extremely metal-poor (EMP) stars in the Galactic Halo provides constraints on theoretical studies of the chemical and stellar evolution of the early Universe. To calculate yields for EMP stars for use in chemical evolution calculations and to test whether such models can account for some of the recent abundance observations of EMP stars, in particular the highly C-rich EMP (CEMP) halo stars. We modify an existing 1D stellar structure code to include time-dependent mixing in a diffusion approximation. Using this code and a post-processing nucleosynthesis code we calculate the structural evolution and nucleosynthesis of a grid of models covering the metallicity range: -6.5<=[Fe/H]<=-3.0 (plus Z=0), and mass range: 0.85<=M<=3.0M_{sun}_, amounting to 20 stars in total.
24649. Yields of Fe and Zn for different types of SNe
ID:
ivo://CDS.VizieR/J/ApJ/855/63
Title:
Yields of Fe and Zn for different types of SNe
Short Name:
J/ApJ/855/63
Date:
21 Oct 2021
Publisher:
CDS
Description:
The heaviest iron-peak element Zinc (Zn) has been used as an important tracer of cosmic chemical evolution. Spectroscopic observations of the metal-poor stars in Local Group galaxies show an increasing trend of [Zn/Fe] ratios toward lower metallicity. However, the enrichment of Zn in galaxies is not well understood due to poor knowledge of astrophysical sites of Zn, as well as metal mixing in galaxies. Here we show possible explanations for the observed trend by taking into account electron-capture supernovae (ECSNe) as one of the sources of Zn in our chemodynamical simulations of dwarf galaxies. We find that the ejecta from ECSNe contribute to stars with [Zn/Fe]>~0.5. We also find that scatters of [Zn/Fe] in higher metallicities originate from the ejecta of type Ia supernovae. On the other hand, it appears difficult to explain the observed trends if we do not consider ECSNe as a source of Zn. These results come from an inhomogeneous spatial metallicity distribution due to the inefficiency of the metal mixing. We find that the optimal value of the scaling factor for the metal diffusion coefficient is ~0.01 in the shear- based metal mixing model in smoothed particle hydrodynamics simulations. These results suggest that ECSNe could be one of the contributors of the enrichment of Zn in galaxies.
24650. Yields of intermediate mass stars
ID:
ivo://CDS.VizieR/J/A+AS/123/305
Title:
Yields of intermediate mass stars
Short Name:
J/A+AS/123/305
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present theoretical yields of H, ^4^He, ^12^C, ^13^C, ^14^N, and ^16^O for stars with initial masses between 0.8 and 8M_{sun}_ and initial metallicities Z=0.001, 0.004, 0.008, 0.02, and 0.04. We use the evolutionary tracks of the Geneva group up to the early asymptotic giant branch (AGB) in combination with a synthetic thermal-pulsing AGB evolution model to follow in detail the chemical evolution and mass loss up to the end of the AGB including the first, second, and third dredge-up phases. Most of the relations used are metallicity dependent to make a realistic comparison with stars of different initial abundances. The effect of Hot Bottom Burning (HBB) is included in an approximate way. The metallicity dependent yields of intermediate mass stars listed in tables (1-38) below are well suited for use in galactic chemical evolution models.

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