- 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.
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1582. 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.
- 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.
- 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.
- 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.
- 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.
- ID:
- ivo://CDS.VizieR/J/AJ/142/127
- Title:
- NGC 5822 UBVI and uvbyCaH{beta} photometry
- Short Name:
- J/AJ/142/127
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC 5822 is a richly populated, moderately nearby, intermediate-age open cluster covering an area larger than the full moon on the sky. A CCD survey of the cluster on the UBVI and uvbyCaH{beta} systems shows that the cluster is superposed upon a heavily reddened field of background stars with E(B-V)>0.35mag, while the cluster has small and uniform reddening at E(b-y)=0.075+/-0.008mag or E(B-V)=0.103+/-0.011mag, based upon 48 and 61 probable A and F dwarf single-star members, respectively. The errors quoted include both internal photometric precision and external photometric uncertainties.
- ID:
- ivo://CDS.VizieR/J/MNRAS/309/739
- Title:
- NGC 2660 UBVIc photometry
- Short Name:
- J/MNRAS/309/739
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present CCD UBVI photometry of the intermediate old open cluster NGC 2660, covering from the red giant region to about seven magnitudes below the main sequence turn-off. Using the synthetic colour-magnitude diagram method, we estimate in a self-consistent way values for distance modulus [(m-M)_0_~12.2], reddening [E(B-V)~0.40], metallicity ([Fe/H] about solar) and age (t<=1Gyr). A 30 per cent population of binary stars turns out to be probably present.
- ID:
- ivo://CDS.VizieR/J/AcA/59/349
- Title:
- NGC 1502 UBVIc photometry
- Short Name:
- J/AcA/59/349
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of variability search in the field of the young open cluster NGC 1502. Eight variable stars were discovered. Of six other stars in the observed field that were suspected for variability, we confirm variability of two, including one beta Cep star, NGC 1502-26. The remaining four suspects were found to be constant in our photometry. In addition, UBVIc photometry of the well-known massive eclipsing binary SZ Cam was obtained.
- ID:
- ivo://CDS.VizieR/J/AJ/115/734
- Title:
- NGC 6231 UBVRI and H{alpha} photometry
- Short Name:
- J/AJ/115/734
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- UBVRI and H{alpha} CCD photometry has been obtained for the young open cluster NGC 6231. From the R-H{alpha} color, a measure of the H{alpha} emission, we find 12 pre-main-sequence (PMS) members and seven possible PMS members in the cluster. Applying recent stellar evolutionary tracks and PMS evolutionary tracks, we derive the age, age spread, and initial mass function of the cluster. The initial mass function of NGC 6231 is a Gaussian with a turnover at logm~0.4 (m~2.5M_{Sun}_) and shows an abrupt decrease in the number of low-mass stars. Possible reasons for the suppression of low-mass star formation and star formation processes are discussed.
