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- ID:
- ivo://CDS.VizieR/J/AJ/149/15
- Title:
- Spectroscopy of NGC 7789
- Short Name:
- J/AJ/149/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained high-resolution spectra of 32 giants in the open cluster NGC 7789 using the Wisconsin-Indiana-Yale-NOAO Hydra spectrograph. We explore differences in atmospheric parameters and elemental abundances caused by the use of the linelist developed for the Gaia-ESO Survey (GES) compared to one based on Arcturus used in our previous work. [Fe/H] values decrease when using the GES linelist instead of the Arcturus-based linelist; these differences are probably driven by systematically lower (~-0.1dex) GES surface gravities. Using the GES linelist we determine abundances for 10 elements--Fe, Mg, Si, Ca, Ti, Na, Ni, Zr, Ba, and La. We find the cluster's average metallicity [Fe/H]=0.03+/-0.07dex, in good agreement with literature values, and a lower [Mg/Fe] abundance than has been reported before for this cluster (0.11+/-0.05dex). We also find the neutron-capture element barium to be highly enhanced--[Ba/Fe]=+0.48+/-0.08--and disparate from cluster measurements of neutron-capture elements La and Zr (-0.08+/-0.05 and 0.08+/-0.08, respectively). This is in accordance with recent discoveries of supersolar Ba enhancement in young clusters along with more modest enhancement of other neutron-capture elements formed in similar environments.
- ID:
- ivo://CDS.VizieR/J/AJ/146/39
- Title:
- Spectroscopy of NGC 5822-2 and NGC 5822-201
- Short Name:
- J/AJ/146/39
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Open clusters are very useful examples to explain the constraint of the nucleosynthesis process with the luminosities of stars because the distances of the clusters are better known than those of field stars. We carried out a detailed spectroscopic analysis to derive the chemical composition of two red giants in the young open cluster NGC 5822, NGC 5822-2, and NGC 5822-201. We obtained abundances of C, N, O, Na, Mg, Al, Ca, Si, Ti, Ni, Cr, Y, Zr, La, Ce, and Nd. The atmospheric parameters of the studied stars and their chemical abundances were determined using high-resolution optical spectroscopy. We employed the local thermodynamic equilibrium model atmospheres of Kurucz and the spectral analysis code MOOG. The abundances of the light elements were derived using the spectral synthesis technique. We found that NGC 5822-2 and -201 have, respectively, a mean overabundance of the elements created by the s-process, "s," with the notation [s/Fe] of 0.77+/-0.12 and 0.83+/-0.05. These values are higher than those for field giants of similar metallicity. We also found that NGC 5822-2 and -201 have, respectively, luminosities of 140L_{sun}_ and 76L_{sun}_, which are much lower than the luminosity of an asymptotic giant branch star. We conclude that NGC 5822-2 and NGC 5822-201 are two new barium stars first identified in the open cluster NGC 5822. The mass transfer hypothesis is the best scenario to explain the observed overabundances.
- ID:
- ivo://CDS.VizieR/J/ApJ/782/8
- Title:
- Spectroscopy of 104 objects in the ONC
- Short Name:
- J/ApJ/782/8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We performed low-resolution (R~40) near-infrared (0.9-2.4{mu}m) multi-object spectroscopy of 240 isolated point sources having apparent H-band magnitudes between 9 and 18 in the central 5'x6' of the Orion Trapezium cluster. The observations were performed over four nights at the Canada-France-Hawaii Telescope using the visiting instrument SIMON, an infrared imager and multi-object spectrograph. We present the spectra of 104 objects with accurately derived spectral types including 7 new objects having masses below the hydrogen-burning limit, and 6 objects with masses below the deuterium-burning limit. The spectral classification is performed by fitting previously classified spectral templates of dwarf stars (K4-M3) and optically classified young stellar and substellar objects (M4-L0), to the entire 0.9-2.4{mu}m spectral energy distribution in order to assign a spectral type and visual extinction for each object. Of the 104 objects studied, 44 have been previously classified spectroscopically using various techniques. We perform a rigorous comparison between the previous classifications and our own and find them to be in good agreement. Using the dereddened H-band magnitudes, the classified objects are used to create an Hertzsprung-Russell diagram for the cluster. We find that the previous age estimates of ~1Myr to be consistent with our results. Consistent with previous studies, numerous objects are observed to have luminosities several magnitudes above the 1Myr isochrone. Numerous objects exhibiting emission features in the J band are also reported.
- ID:
- ivo://CDS.VizieR/J/MNRAS/393/272
- Title:
- Spectroscopy of red giants in 12 open clusters
- Short Name:
- J/MNRAS/393/272
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Near-infrared spectra of 133 red giant stars from 10 Galactic open clusters and two Galactic globular clusters spanning 2.2dex in metallicity and 11Gyr in age are presented. We combine this sample with 10 clusters from Cole and collaborators (2004MNRAS.347..367C) to investigate the CaII triplet line strengths and their relation to cluster metallicity and position along the red giant branch. We show that characterizing the stellar surface gravity using K_s_-band photometry (relative to the horizontal branch) taken from the Two Micron All-Sky Survey allows for metallicity measurements at least as precise as those derived using V- or I-band data. This has the great advantage that uniform photometry and reliable astrometry are available for a large number of clusters. Using K_s_-band photometry also reduces the effect of differential reddening within a given cluster. We find no significant evidence for age or metallicity effects to the linear CaII triplet-metallicity relationship over the small range in magnitudes studied when homogeneous reference metallicities are used. We derive the first spectroscopic metallicity and new radial velocity estimates for five open clusters: Berkeley 81, Berkeley 99, IC 1311, King 2 and NGC7044. King2 has an anomalous radial velocity compared with the local disc population. We discuss the possibility that it is part of the Monoceros tidal stream.
- ID:
- ivo://CDS.VizieR/J/AJ/150/204
- Title:
- Spectroscopy of standard stars
- Short Name:
- J/AJ/150/204
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We define an H{alpha} photometric system that is designed as a companion to the well established H{beta} index. The new system is built on spectrophotometric observations of field stars as well as stars in benchmark open clusters. We present data for 75 field stars, 12 stars from the Coma star cluster, 24 stars from the Hyades, 17 stars from the Pleiades, and 8 stars from NGC 752 to be used as primary standard stars in the new systems. We show that the system transformations are relatively insensitive to the shape of the filter functions. We make comparisons of the H{alpha} index to the H{beta} index and illustrate the relationship between the two systems. In addition, we present relations that relate both hydrogen indices to equivalent width and effective temperature. We derive equations to calibrate both systems for Main Sequence stars with spectral types in the range O9 to K2 for equivalent width and A2 to K2 for effective temperature.
- ID:
- ivo://CDS.VizieR/J/A+A/651/A104
- Title:
- Spiral arms Gaia EDR3
- Short Name:
- J/A+A/651/A104
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Using the astrometry and integrated photometry from the Gaia Early Data Release 3 (EDR3), we map the density variations in the distribution of young Upper Main Sequence (UMS) stars, open clusters and classical Cepheids in the Galactic disk within several kiloparsecs of the Sun. Maps of relative over/under-dense regions for UMS stars in the Galactic disk are derived, using both bivariate kernel density estimators and wavelet transformations. The resulting overdensity maps exhibit large-scale arches, that extend in a clumpy but coherent way over the entire sampled volume, indicating the location of the spiral arms segments in the vicinity of the Sun. Peaks in the UMS overdensity are well-matched by the distribution of young and intrinsically bright open clusters. By applying a wavelet transformation to a sample of classical Cepheids, we find that their overdensities possibly extend the spiral arm segments on a larger scale (~10kpc from the Sun). While the resulting map based on the UMS sample is generally consistent with previous models of the Sagittarius-Carina spiral arm, the geometry of the arms in the III quadrant (galactic longitudes 180{deg}<l<270{deg}) differs significantly from many previous models. In particular we find that our maps favour a larger pitch angle for the Perseus arm, and that the Local Arm extends into the III quadrant at least 4kpc past the Sun's position, giving it a total length of at least 8kpc.
- ID:
- ivo://CDS.VizieR/J/ApJ/796/127
- Title:
- Spitzer h and {chi} Persei candidate members
- Short Name:
- J/ApJ/796/127
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze very deep Infrared Array Camera and Multiband Imaging Photometer for Spitzer (MIPS) photometry of ~12500 members of the 14 Myr old Double Cluster, h and {chi} Persei, building upon our earlier, shallower Spitzer Cycle 1 studies. Numerous likely members show infrared (IR) excesses at 8 {mu}m and 24 {mu}m, indicative of circumstellar dust. The frequency of stars with 8 {mu}m excess is at least 2% for our entire sample, slightly lower (higher) for B/A stars (later type, lower mass stars). Optical spectroscopy also identifies gas in about 2% of systems, but with no clear trend between the presence of dust and gas. Spectral energy distribution modeling of 18 sources with detections at optical wavelengths through MIPS 24 {mu}m reveals a diverse set of disk evolutionary states, including a high fraction of transitional disks, though similar data for all disk-bearing members would provide constraints. Using Monte Carlo simulations, we combine our results with those for other young clusters to study the global evolution of dust/gas disks. For nominal cluster ages, the e-folding times ({tau}_0_) for the frequency of warm dust and gas are 2.75 Myr and 1.75 Myr, respectively. Assuming a revised set of ages for some clusters, these timescales increase to 5.75 and 3.75 Myr, respectively, implying a significantly longer typical protoplanetary disk lifetime than previously thought. In both cases, the transitional disk duration, averaged over multiple evolutionary pathways, is ~1 Myr. Finally, 24 {mu}m excess frequencies for 4-6 M_{sun}_ stars appear lower than for 1-2.5 M_{sun}_ stars in other 10-30 Myr old clusters.
- ID:
- ivo://CDS.VizieR/J/ApJ/660/1532
- Title:
- Spitzer/IRAC-MIPS survey of NGC 2244
- Short Name:
- J/ApJ/660/1532
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results from a survey of NGC 2244 from 3.6 to 24um with the Spitzer Space Telescope. The 24um-8um-3.6um color composite image of the region shows that the central cavity surrounding the multiple O and B stars of NGC 2244 contains a large amount of cool dust visible only at 24um. Our survey gives a detailed look at disk survivability within the hot-star-dominated environment in this cavity. Using mid-infrared two-color diagrams ([3.6]-[4.5] vs. [5.8]-[8.0]), we identified 337 class II and 25 class I objects out of 1084 objects detected in all four of these bands with photometric uncertainty better than 10%. Including the 24um data, we found 213 class II and 20 class I sources out of 279 stars also detected at this latter band. The center of the class II density contours is in very good agreement with the center of the cluster detected in the 2MASS images. We studied the distribution of the class II sources relative to the O stars and found that the effect of high-mass stars on the circumstellar disks is significant only in their immediate vicinity.
- ID:
- ivo://CDS.VizieR/J/AJ/145/66
- Title:
- Spitzer light curves of YSOs in IC 348
- Short Name:
- J/AJ/145/66
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on synoptic observations at 3.6 and 4.5{mu}m of young stellar objects in IC 348 with 38epochs covering 40days. We find that among the detected cluster members, 338 at [3.6] and 269 at both [3.6] and [4.5], many are variable on daily to weekly timescales with typical fluctuations of ~0.1mag. The fraction of variables ranges from 20% for the diskless pre-main sequence stars to 60% for the stars still surrounded by infalling envelopes. We also find that stars in the exposed cluster core are less variable than the stars in the dense, slightly younger, southwestern ridge. This trend persists even after accounting for the underlying correlation with infrared spectral energy distribution type, suggesting that the change in variable fraction is not simply a reflection of the change in relative fraction of class I versus class II sources across the cloud, but instead reflects a change in variability with age. We also see a strong correlation between infrared variability and X-ray luminosity among the class II sources. The observed variability most likely reflects large changes in the structure of the inner wall located at the dust sublimation radius. We explore the possibility that these structural perturbations could be caused by a hot spot on the star heating dust above the sublimation temperature, causing it to evaporate rapidly, and increasing the inner radius for a portion of the disk. Under a number of simplifying assumptions we show that this model can reproduce the size and timescale of the 3.6 and 4.5{mu}m fluctuations. Regardless of its source, the infrared variability indicates that the inner disk is not a slowly evolving entity, but instead is a bubbling, warped, dented mass of gas and dust whose global size and shape fluctuate in a matter of days.
