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4441. NGC 6866 proper motions and CCD photometry
ID:
ivo://CDS.VizieR/J/PAZh/36/354
Title:
NGC 6866 proper motions and CCD photometry
Short Name:
J/PAZh/36/354
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of our comprehensive study of the Galactic open star cluster NGC 6866. The positions of stars in the investigated region have been obtained with the "Fantasy "automatic measuring machine from 10 plates of the normal astrograph at the Pulkovo Astronomical Observatory. The size of the investigated field is 40x40arcmin^2^, the limiting magnitude is B<=16.6mag, and the maximum epoch difference is 79yr. For 1202 field stars we have determined the relative proper motions with a rms error of 0.5mas/yr. Out of them 413 stars may be considered cluster members with a probability P>70% according to the astrometric criterion. Photometric diagrams have been used as an additional criterion. We have performed two-color BV CCD photometry of stars with the Pulkovo ZA-320M mirror astrograph. The U magnitudes from the literature have also been used to construct the two-color diagrams. A total of 267 stars have turned out to be members of NGC 6866 according to the two criteria. We present refined physical parameters of the cluster and its age estimate (5.6x10^8^yr). The cluster membership of red and blue giants, variable, double, and multiple stars is considered. We have found an almost complete coincidence of the positions of one of the stars in the region (a cluster nonmember) and a soft X-ray source in the ROSAT catalog. The "Fantasy " automatic measuring machine is described in the Appendix. DOI:10.1134/S106377371005004X
4442. NGC 2068/2071 protoclusters
ID:
ivo://CDS.VizieR/J/A+A/372/L41
Title:
NGC 2068/2071 protoclusters
Short Name:
J/A+A/372/L41
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report on a wide-field submillimeter continuum survey of the NGC 2068/2071 protoclusters in the Orion B cloud complex. We used the SCUBA bolometer array on JCMT to map a 32'x18' region in size (~4pcx2pc) at 850 and 450 microns. Our survey shows that the dense cores mapped in CS(2-1) by Lada et al. (1991ApJ...368..432L) and labelled with LBS numbers break up into 82 small-scale (~5000AU) fragments. The latter include 70 starless condensations, believed to be the immediate progenitors of accreting protostars, and 5 circumstellar envelopes/disks around protostars. The nature of the 7 remaining cloud fragments is unclear because their dust continuum emission is largely contaminated by line emission.
4443. NGC 352 R-band image
ID:
ivo://CDS.VizieR/J/A+A/647/A20
Title:
NGC 352 R-band image
Short Name:
J/A+A/647/A20
Date:
21 Oct 2021
Publisher:
CDS
Description:
This paper is a contribution to the discussion about whether the X/peanut component is part of the bar, or the bar itself. Our goal is to present a clear-cut case of a barred-spiral galaxy in which all structural components (i.e. the thick and thin part of the bar and the spiral arms) can be observed in its image and their dimensions directly measured there. We obtained deep images of the nearby galaxy NGC 352, which has an ideal inclination allowing us to observe all of the parts that compose its morphology, estimate their relative sizes, and determine the topology of the luminous matter of this galaxy. We successfully compare our findings with the existence and the relative dimensions of the corresponding components encountered in the disc of a GADGET N-body model. NGC 352 is a barred spiral galaxy with a bar of about 13 kpc radius. Its bar has a central thick part that extends up to a distance about 5kpc from the centre of the galaxy along its major axis, while its thickness reaches a height of 3.8kpc. Thus, the thick part of the bar occupies the central part of the bar component, and its length is about 40% of that of the thin bar. The branches of the X-feature are characterised by the presence of 'hooks' at their extremities. The profile along the major axis of the bar is characterised by the presence of 'shoulders', the end of which is associated with local surface brightness enhancements on the equatorial plane. A central disc with a spiral-like feature embedded in it dominates in the innermost 1.7kpc. NGC 352 offers a case in which we directly observe that the X/peanut component is unambiguously part of the bar. This boxy structure is neither a separate bulge component nor the bar itself. The relative extent of the peanut with respect to the bar is well inside the range predicted in the majority of the simulated N-body bars. The hooks of the X-feature and the local surface brightness enhancements on the equatorial plane have their counterparts in surface density features of models based on the orbital theory, as well as of models based on response calculations and of fully selfconsistent N-body calculations.
4444. NGC 7538 region YSOs
ID:
ivo://CDS.VizieR/J/MNRAS/467/2943
Title:
NGC 7538 region YSOs
Short Name:
J/MNRAS/467/2943
Date:
21 Oct 2021
Publisher:
CDS
Description:
Deep optical photometric data on the NGC 7538 region were collected and combined with archival data sets from the Chandra, 2MASS and Spitzer surveys to generate a new catalogue of young stellar objects (YSOs) including those not showing infrared excess emission. This new catalogue is complete down to 0.8M_{sun}_. The nature of the YSOs associated with the NGC 7538 region and their spatial distribution are used to study the star-formation process and the resultant mass function (MF) in the region. Out of the 419 YSOs, ~91 per cent have ages between 0.1 and 2.5Myr and ~86 per cent have masses between 0.5 and 3.5M_{sun}_, as derived by the spectral energy distribution fitting analysis. Around 24, 62 and 2 per cent of these YSOs are classified to be class I, class II and class III sources, respectively. The X-ray activities for the class I, class II and class III objects are not significantly different from each other. This result implies that the enhanced X-ray surface flux due to the increase in the rotation rate may be compensated for by the decrease in the stellar surface area during the pre-main-sequence evolution. Our analysis shows that the O3V type high-mass star IRS 6 may have triggered the formation of young low-mass stars up to a radial distance of 3pc. The MF shows a turn-off at around 1.5M_{sun}_ and the value of its slope {Gamma} in the mass range 1.5<M/M_{sun}_<6 is -1.76+/-0.24, which is steeper than the Salpeter value.
4445. NGC 1960 (RI)c photometric catalogue
ID:
ivo://CDS.VizieR/J/MNRAS/434/2438
Title:
NGC 1960 (RI)c photometric catalogue
Short Name:
J/MNRAS/434/2438
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a deep Cousins RI photometric survey of the open cluster NGC 1960, complete to R_C_=~22, I_C_=~21, that is used to select a sample of very low mass cluster candidates. Gemini spectroscopy of a subset of these is used to confirm membership and locate the age-dependent 'lithium depletion boundary' (LDB) - the luminosity at which lithium remains unburned in its low-mass stars. The LDB implies a cluster age of 22+/-4Myr and is quite insensitive to choice of evolutionary model. NGC 1960 is the youngest cluster for which a LDB age has been estimated and possesses a well-populated upper main sequence and a rich low-mass pre-main sequence. The LDB age determined here agrees well with precise age estimates made for the same cluster based on isochrone fits to its high- and low-mass populations. The concordance between these three age estimation techniques, that rely on different facets of stellar astrophysics at very different masses, is an important step towards calibrating the absolute ages of young open clusters and lends confidence to ages determined using any one of them.
4446. NGC 6819 stellar radial-velocity and photometry
ID:
ivo://CDS.VizieR/J/AJ/138/159
Title:
NGC 6819 stellar radial-velocity and photometry
Short Name:
J/AJ/138/159
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the current results from our ongoing radial-velocity (RV) survey of the intermediate-age (2.4Gyr) open cluster NGC 6819. Using both newly observed and other available photometry and astrometry, we define a primary target sample of 1454 stars that includes main-sequence, subgiant, giant, and blue straggler stars, spanning a magnitude range of 11<=V<=16.5 and an approximate mass range of 1.1-1.6M_{sun}_. Our sample covers a 23 arcminute (13pc) square field of view centered on the cluster. We have measured 6571 radial velocities for an unbiased sample of 1207 stars in the direction of the open cluster NGC 6819, with a single-measurement precision of 0.4km/s for most narrow-lined stars. We use our RV data to calculate membership probabilities for stars with >=3 measurements, providing the first comprehensive membership study of the cluster core that includes stars from the giant branch through the upper main sequence. We identify 480 cluster members. Additionally, we identify velocity-variable systems, all of which are likely hard binaries that dynamically power the cluster.
4447. NGC 2345 Stroemgren photometry
ID:
ivo://CDS.VizieR/J/A+A/631/A124
Title:
NGC 2345 Stroemgren photometry
Short Name:
J/A+A/631/A124
Date:
21 Oct 2021
Publisher:
CDS
Description:
NGC 2345 is a young open cluster hosting seven blue and red supergiants, low metallicity and a high fraction of Be stars which makes it a privileged laboratory to study stellar evolution. We aim to improve the determination of the cluster parameters and study the Be phenomenon. Our objective is also to characterise its seven evolved stars by deriving their atmospheric parameters and chemical abundances. We performed a complete analysis combining for the first time ubvy photometry with spectroscopy as well as Gaia Data Release 2. We obtained spectra with classification purposes for 76 stars and high-resolution spectroscopy for an in-depth analysis of the blue and red evolved stars. We identify a new red supergiant and 145 B-type likely members within a radius of 18.7+/-1.2arcmin, which implies an initial mass, M_cl_~5,200M_{sun}_. We find a distance of 2.5+/-0.2kpc for NGC 2345, placing it at R_GC_=10.2+/-0.2kpc. Isochrone fitting supports an age of 56+/-13Ma, implying masses around 6.5M_{sun}_ for the supergiants. A high fraction of Be stars (~10%) is found. From the spectral analysis we estimate for the cluster an average v_rad}_=+58.6+/-0.5km/1 and a low metallicity, [Fe/H]=-0.28+/-0.07. We also have determined chemical abundances for Li, O, Na, Mg, Si, Ca, Ti, Ni, Rb, Y, and Ba for the evolved stars. The chemical composition of the cluster is consistent with that of the Galactic thin disc. One of the K supergiants, S50, is a Li-rich star, presenting an A(Li)~2.1. An overabundance of Ba is found, supporting the enhanced s-process. NGC 2345 has a low metallicity for its Galactocentric distance, comparable to typical LMC stars. It is massive enough to serve as a testbed for theoretical evolutionary models for massive intermediate-mass stars.
4448. NGC2264 structure and star formation history
ID:
ivo://CDS.VizieR/J/A+A/609/A10
Title:
NGC2264 structure and star formation history
Short Name:
J/A+A/609/A10
Date:
21 Oct 2021
Publisher:
CDS
Description:
Reconstructing the structure and history of young clusters is pivotal to understanding the mechanisms and timescales of early stellar evolution and planet formation. Recent studies suggest that star clusters often exhibit a hierarchical structure, possibly resulting from several star formation episodes occurring sequentially rather than a monolithic cloud collapse. We aim to explore the structure of the open cluster and star-forming region NGC 2264 (~3Myr), which is one of the youngest, richest and most accessible star clusters in the local spiral arm of our Galaxy; we link the spatial distribution of cluster members to other stellar properties such as age and evolutionary stage to probe the star formation history within the region. We combined spectroscopic data obtained as part of the Gaia-ESO Survey (GES) with multi-wavelength photometric data from the Coordinated Synoptic Investigation of NGC 2264 (CSI 2264) campaign. We examined a sample of 655 cluster members, with masses between 0.2 and 1.8M_{sun}_ and including both disk-bearing and disk-free young stars. We used Teff estimates from GES and g,r,i photometry from CSI 2264 to derive individual extinction and stellar parameters.
4449. NGC 6383 T Tauri accretion rates
ID:
ivo://CDS.VizieR/J/MNRAS/484/5102
Title:
NGC 6383 T Tauri accretion rates
Short Name:
J/MNRAS/484/5102
Date:
03 Nov 2021 13:02:39
Publisher:
CDS
Description:
This paper presents optical (ugriH{alpha})-infrared (JHKs, 3.6-8.0um) photometry and Gaia astrometry of 55 Classical T-Tauri stars (CTTS) in the star-forming region Sh 2-012 and its central cluster NGC 6383. The sample was identified based on photometric H{alpha} emission linewidths, and has a median age of 2.8+/-1.6Myr, with a mass range between 0.3 and 1M_{sun}_. 94 per cent of CTTS with near-infrared cross-matches fall on the near-infrared T-Tauri locus, with all stars having mid-infrared photometry exhibiting evidence for accreting circumstellar discs. CTTS are found concentrated around the central cluster NGC 6383, and towards the bright rims located at the edges of Sh 2-012. Stars across the region have similar ages, suggestive of a single burst of star formation. Mass accretion rates dMacc/dt) estimated via H{alpha} and u-band line intensities show a scatter (0.3dex) similar to spectroscopic studies, indicating the suitability of H{alpha} photometry to estimate dMacc/dt. Examining the variation of dMacc/dt with stellar mass (M*), we find a smaller intercept in the (dMacc/dt)-M* relation than oft-quoted in the literature, providing evidence to discriminate between competing theories of protoplanetary disc evolution.
4450. NGC 2264 T Tauri star properties
ID:
ivo://CDS.VizieR/J/MNRAS/429/1981
Title:
NGC 2264 T Tauri star properties
Short Name:
J/MNRAS/429/1981
Date:
21 Oct 2021
Publisher:
CDS
Description:
There are many pertinent open issues in the area of star and planet formation. Large statistical samples of young stars across star-forming regions are needed to trigger a breakthrough in our understanding, but most optical studies are based on a wide variety of spectrographs and analysis methods, which introduces large biases. Here we show how graphical Bayesian networks can be employed to construct a hierarchical probabilistic model which allows pre-main-sequence ages, masses, accretion rates and extinctions to be estimated using two widely available photometric survey data bases (Isaac Newton Telescope Photometric H{alpha} Survey r'/H{alpha}/i' and Two Micron All Sky Survey J-band magnitudes). Because our approach does not rely on spectroscopy, it can easily be applied to homogeneously study the large number of clusters for which Gaia will yield membership lists. We explain how the analysis is carried out using the Markov chain Monte Carlo method and provide python source code. We then demonstrate its use on 587 known low-mass members of the star-forming region NGC 2264 (Cone Nebula), arriving at a median age of 3.0Myr, an accretion fraction of 20+/-2 per cent and a median accretion rate of 10-8.4M{sun}/yr. The Bayesian analysis formulated in this work delivers results which are in agreement with spectroscopic studies already in the literature, but achieves this with great efficiency by depending only on photometry. It is a significant step forward from previous photometric studies because the probabilistic approach ensures that nuisance parameters, such as extinction and distance, are fully included in the analysis with a clear picture on any degeneracies.