- ID:
- ivo://CDS.VizieR/J/A+A/607/A86
- Title:
- NGC 6334 and NGC 6357 OB stars spectra
- Short Name:
- J/A+A/607/A86
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The formation of high mass stars is still debated. For this reason, several projects, as the Herschel-HOBYS are focussed on the study of the earliest phases of massive star formation. As a result, massive star-forming complexes such as NGC 6334 and NGC 6357 have been observed in the far-infrared to study their massive dense cores where massive stars are expected to form. However, to better characterise the environment of these cores we need to understand the previous massive star formation history. To better characterize the environment of these massive dense cores we propose to study the previous high mass star formation and how these stars act on their environment. This study is based on spectral classification of the OB stars identified towards NGC 6334 and NGC 6357 with spectra taken with the AAOmega spectrograph on the Anglo-Australian Telescope (AAT). From the subsequent spectral classification of 109 stars across these regions we have been able to evaluate the following: distance, age, mass, global star-forming efficiency (SFE) and star-formation rate (SFR) of the regions. The physical conditions of the ionised gas for both complexes was also derived. We confirm that NGC 6334 and NGC 6357 belong to the Saggitarius-Carina arm which, in this direction, extends from 1kpc to 2.2kpc. From the location of the stars in Hertzprung-Russell diagram we show that stars older than ~10Myr are broadly spread across these complexes while younger stars are mainly located in the H ii regions and stellar clusters. Our data also suggests that some of the young stars can be considered as runaway stars. We evaluate a SFE of 0.019 and 0.021 and a SFR of 1.1x10^3^M_{sun}/Myr^ and 1.7x10^3^M_{sun}_/Myr for NGC 6334 and NGC 6357 respectively. We note that 25 OB stars have X-ray counterparts, most of them belonging to NGC 6357. This suggests that molecular clouds in NGC 6357 is more impacted by X-ray flux and stellar winds than for NGC 6334. Finally, from analysis of nebular lines (H{alpha}, [NII] and [SII]) from spectra from several regions of ionised gas, we confirm that the filaments in NGC 6357 are shock heated.
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Search Results
262. 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/BaltA/12/323
- Title:
- NGC 1750 + 1758 Vilnius photometry
- Short Name:
- J/BaltA/12/323
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Seven-color photometry in the Vilnius system has been obtained for 420 stars down to V=16mag in the area containing the overlapping open clusters NGC 1750 and NGC 1758 in Taurus. Spectral and luminosity classes, color excesses, interstellar extinctions and distances are given for 287 stars. The classification of stars is based on their reddening-free Q-parameters. 18 stars observed photoelectrically were used as standards.
- ID:
- ivo://CDS.VizieR/J/ApJ/875/L9
- Title:
- ODISEA: Disk dust mass distributions
- Short Name:
- J/ApJ/875/L9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- As protostars evolve from optically faint/infrared-bright (Class I) sources to optically bright/infrared-faint (Class II) the solid material in their surrounding disks accumulates into planetesimals and protoplanets. The nearby, young Ophiuchus star-forming region contains hundreds of protostars in a range of evolutionary states. Using the Atacama Large Millimeter Array to observe their millimeter continuum emission, we have measured masses of, or placed strong upper limits on, the dust content of 279 disks. The masses follow a log-normal distribution with a clear trend of decreasing mass from less to more evolved protostellar infrared class. The (logarithmic) mean Class I disk mass, M=3.8M_{Earth}_, is about 5 times greater than the mean Class II disk mass, but the dispersion in each class is so high, {sigma}_logM_~0.8-1, that there is a large overlap between the two distributions. The disk mass distribution of flat-spectrum protostars lies in between Classes I and II. In addition, three Class III sources with little to no infrared excess are detected with low disk masses, M~0.3M_{Earth}_. Despite the clear trend of decreasing disk mass with protostellar evolutionary state in this region, a comparison with surveys of Class II disks in other regions shows that masses do not decrease monotonically with age. This suggests that the cloud-scale environment may determine the initial disk mass scale or that there is substantial dust regeneration after 1Myr.
- ID:
- ivo://CDS.VizieR/J/MNRAS/385/905
- Title:
- OGLEII high pm stars towards Galactic Centre
- Short Name:
- J/MNRAS/385/905
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The photometry data base of the second phase of the OGLE microlensing experiment, OGLE-II, is a rich source of information about the kinematics and structure of the Galaxy. In this work, we use the OGLE-II proper motion catalogue to identify candidate stars which have high proper motions. 521 stars with proper motion {mu}>50mas/yr in the OGLE-II proper motion catalogue were cross-identified with stars in the MACHO high proper motion catalogue, and the DEep Near-Infrared Survey and Two-Micron All-Sky Survey infrared photometry catalogues. Photometric distances were computed for stars with colours consistent with G/K- and M-type stars. Six stars were newly identified as possible nearby (<50pc) M dwarfs.
- ID:
- ivo://CDS.VizieR/J/MNRAS/458/3012
- Title:
- OGLE-III Parallax microlensing events
- Short Name:
- J/MNRAS/458/3012
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Most stellar remnants so far have been found in binary systems, where they interact with matter from their companions. Isolated neutron stars and black holes are difficult to find as they are dark, yet they are predicted to exist in our Galaxy in vast numbers. We explored the OGLE-III data base of 150 million objects observed in years 2001-2009 and found 59 microlensing events exhibiting a parallax effect due to the Earth's motion around the Sun. Combining parallax and brightness measurements from microlensing light curves with expected proper motions in the Milky Way, we identified 13 microlensing events which are consistent with having a white dwarf, neutron star or a black hole lens and we estimated their masses and distances. The most massive of our black hole candidates has 9.3M_{sun}_ and is at a distance of 2.4kpc. The distribution of masses of our candidates indicates a continuum in mass distribution with no mass gap between neutron stars and black holes. We also present predictions on how such events will be observed by the astrometric Gaia mission.
- ID:
- ivo://CDS.VizieR/J/A+A/644/A95
- Title:
- omega Cen RR Lyrae and Type II Cepheids
- Short Name:
- J/A+A/644/A95
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The separation between RR Lyrae (RRLs) and type II Cepheid (T2Cs) variables based on their period is debated. Both types of variable stars are distance indicators, and we aim to promote the use of T2Cs as distance indicators in synergy with RRLs. We adopted new and existing optical and Near-Infrared (NIR) photometry of omega Cen to investigate several diagnostics (colour-magnitude diagram, Bailey diagram, Fourier decomposition of the light curve, amplitude ratios) for the empirical separation between Type II Cepheids (T2Cs) and RR Lyrae (RRLs). We also derived NIR period-luminosity relations and found a distance modulus of 13.65+/-0.07 (err.)+/-0.01 (sigma) mag, in agreement with the recent literature. We also found that RRLs and T2Cs obey the same PL relations in the NIR.
- ID:
- ivo://CDS.VizieR/J/ApJ/912/162
- Title:
- Open clusters in solar neighborhood
- Short Name:
- J/ApJ/912/162
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze the 3D morphology and kinematics of 13 open clusters (OCs) located within 500pc of the Sun, using Gaia} EDR3 and kinematic data from literature. Members of OCs are identified using the unsupervised machine learning method StarGO, using 5D parameters (X, Y, Z, {mu}_{alpha}cos{delta}, {mu}_{delta}). The OC sample covers an age range of 25Myr-2.65Gyr. We correct the asymmetric distance distribution due to the parallax error using Bayesian inversion. The uncertainty in the corrected distance for a cluster at 500pc is 3.0-6.3pc, depending on the intrinsic spatial distribution of its members. We determine the 3D morphology of the OCs in our sample and fit the spatial distribution of stars within the tidal radius in each cluster with an ellipsoid model. The shapes of the OCs are well-described with oblate spheroids (NGC 2547, NGC 2516, NGC 2451A, NGC 2451B, NGC 2232), prolate spheroids (IC 2602, IC 4665, NGC 2422, Blanco 1, Coma Berenices), or triaxial ellipsoids (IC 2391, NGC 6633, NGC 6774). The semi-major axis of the fitted ellipsoid is parallel to the Galactic plane for most clusters. Elongated filament-like substructures are detected in three young clusters (NGC 2232, NGC 2547, NGC 2451B), while tidal-tail-like substructures (tidal tails) are found in older clusters (NGC 2516, NGC 6633, NGC 6774, Blanco 1, Coma Berenices). Most clusters may be super-virial and expanding. N-body models of rapid gas expulsion with an SFE of ~1/3 are consistent with clusters more massive than 250M_{sun}_, while clusters less massive than 250M_{sun}_ tend to agree with adiabatic gas expulsion models. Only six OCs (NGC 2422, NGC 6633, and NGC 6774, NGC 2232, Blanco 1, Coma Berenices) show clear signs of mass segregation.
- ID:
- ivo://CDS.VizieR/J/AJ/159/153
- Title:
- Optical and IR photometry in the HII region Sh2-242
- Short Name:
- J/AJ/159/153
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present here identification and characterization of the young stellar population associated with an active star-forming site Sh2-242. We used our own new optical imaging and spectroscopic observational data, as well as several archival catalogs, e.g., Pan-STARRS-1, Gaia-DR2, Isaac Newton Telescope Photometric H-Alpha Survey (IPHAS), Wide-field InfraRed Camera, 2MASS, and Spitzer. Slit spectroscopic results confirm the classification of the main ionizing source BD+26980 as an early-type star of spectral type B0.5V. The spectrophotometric distance of the star is estimated as 2.08{+/-}0.24kpc, which confirms the source as a member of the cluster. An extinction map covering a large area (diameter ~50') is generated with H and K photometry toward the region. From the map, three distinct locations of peak extinction complexes (A_V_~7-17mag) are identified for the very first time. Using the infrared color excess, a total of 33 Class I and 137 Class II young objects are classified within the region. The IPHAS photometry reveals classification of 36 H{alpha} emitting sources, which might be class II objects. Among 36 H{alpha} emitting sources, 5 are already identified using infrared excess emission. In total, 201 young objects are classified toward S242 from this study. The membership status of the young sources is further windowed with the inclusion of parallax from the Gaia DR2 catalog. Using the optical and infrared color-magnitude diagrams, the young stellar objects are characterized with an average age of ~1Myr and masses in the range 0.1-3.0M_{sun}_.
- ID:
- ivo://CDS.VizieR/J/ApJ/612/481
- Title:
- Optical brightness of {epsilon} Eri dust ring
- Short Name:
- J/ApJ/612/481
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The STIS CCD camera on the Hubble Space Telescope (HST) was used to take deep optical images near the K2 V main-sequence star {epsilon} Eridani in an attempt to find an optical counterpart of the dust ring previously imaged by submillimeter observations. Upper limits for the optical brightness of the dust ring are determined and discussed in the context of the scattered starlight expected from plausible dust models.
