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- ID:
- ivo://CDS.VizieR/J/A+A/612/A50
- Title:
- New massive members of Cygnus OB2
- Short Name:
- J/A+A/612/A50
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Cygnus complex is one of the most powerful star forming regions at a close distance from the Sun (~1.4kpc). Its richest OB association Cygnus OB2 is known to harbor many tens of O-type stars and hundreds of B-type stars, providing a large homogeneous population of OB stars that can be analyzed. Many studies of its massive population have been developed in the last decades, although the total number of OB stars is still incomplete. Our aim is to increase the sample of O and B members of Cygnus OB2 and its surroundings by spectroscopically classifying 61 candidates as possible OB-type members of Cygnus OB2, using new intermediate resolution spectroscopy. We have obtained intermediate resolution (R~5000) spectra for all of the OB-type candidates between 2013 and 2017. We thus performed a spectral classification of the sample using HeI-II and metal lines rates, as well as the Marxist Ghost Buster (MGB) software for O-type stars and the IACOB standards catalog for B-type stars. From the whole sample of 61 candidates, we have classified 42 stars as new massive OB-type stars, earlier than B3, in Cygnus OB2 and surroundings, including 11 O-type stars. The other candidates are discarded as they display later spectral types inconsistent with membership in the association. We have also obtained visual extinctions for all the new confirmed massive OB members, placing them in a Hertzsprung-Russell Diagram using calibrations for Teff and luminosity. Finally, we have studied the age and extinction distribution of our sample within the region. We have obtained new blue intermediate-resolution spectra suitable for spectral classification of 61 OB candidates in Cygnus OB2 and surroundings. The confirmation of 42 new OB massive stars (earlier than B3) in the region allows us to increase the young massive population known in the field. We have also confirmed the correlation between age and Galactic longitude previously found in the region. We conclude that many O and early B stars at B>16mag are still undiscovered in Cygnus.
- ID:
- ivo://CDS.VizieR/J/MNRAS/450/3855
- Title:
- New OB star candidates in Carina Arm
- Short Name:
- J/MNRAS/450/3855
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- O and early B stars are at the apex of galactic ecology, but in the Milky Way, only a minority of them may yet have been identified. We present the results of a pilot study to select and parametrize OB star candidates in the Southern Galactic plane, down to a limiting magnitude of g=20. A 2 deg^2^ field capturing the Carina Arm around the young massive star cluster, Westerlund 2, is examined. The confirmed OB stars in this cluster are used to validate our identification method, based on selection from the (u-g, g-r) diagram for the region. Our Markov Chain Monte Carlo fitting method combines VPHAS+ u, g, r, i with published J, H, K photometry in order to derive posterior probability distributions of the stellar parameters log(Teff) and distance modulus, together with the reddening parameters A_0_ and R_V_. The stellar parameters are sufficient to confirm OB status while the reddening parameters are determined to a precision of {sigma}(A_0_)~0.09 and {sigma}(R_V_)~0.08. There are 489 objects that fit well as new OB candidates, earlier than ~ B2. This total includes 74 probable massive O stars, 5 likely blue supergiants and 32 reddened subdwarfs. This increases the number of previously known and candidate OB stars in the region by nearly a factor of 10. Most of the new objects are likely to be at distances between 3 and 6 kpc. We have confirmed the results of previous studies that, at these longer distances, these sight lines require non-standard reddening laws with 3.5<R_V_<4.
- 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.
- ID:
- ivo://CDS.VizieR/J/A+AS/35/347
- Title:
- OB and Supergiants stars in LMC
- Short Name:
- J/A+AS/35/347
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Two regions in the Large Magellanic Cloud, centered at 05:11-66:08 (34B) and 05:27-72:15 (47B) have been searched for OB and supergiant stars. A catalogue of 312 stars is presented in which objective prism spectral types, positions (1975), approximate B magnitudes and cross-identifications are given.
- ID:
- ivo://CDS.VizieR/J/MNRAS/313/43
- Title:
- OB association members in ACT+TRC Catalogs
- Short Name:
- J/MNRAS/313/43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Hipparcos Catalogue (Cat. I/239) contains members of nearby OB associations brighter than 12th magnitude in V. However, membership lists are complete only to magnitude V=7.3. In this paper we discuss whether proper motions listed in the `Astrographic Catalogue+Tycho' reference catalogue (ACT, Cat. I/246) and the Tycho Reference Catalogue (TRC, Cat. I/250), which are complete to V~10.5mag, can be used to find additional association members. Proper motions in the ACT/TRC have an average accuracy of ~3mas/yr. We search for ACT/TRC stars which have proper motions consistent with the spatial velocity of the Hipparcos members of the nearby OB associations already identified by de Zeeuw et al. (1999, Cat. J/AJ/117/354). These stars are first selected using a convergent-point method, and then subjected to further constraints on the proper-motion distribution, magnitude and colour to narrow down the final number of candidate members. Monte Carlo simulations show that the proper-motion distribution, magnitude, and colour constraints remove ~97% of the field stars, while at the same time retain more than 90% of the cluster stars. The procedure has been applied to five nearby associations: the three subgroups of Sco OB2, plus Per OB3 and Cep OB6. In all cases except Cep OB6, we find evidence for new association members fainter than the completeness limit of the Hipparcos Catalogue. However, narrow-band photometry and/or radial velocities are needed to pinpoint the cluster members, and to study their physical characteristics.
- ID:
- ivo://CDS.VizieR/J/AJ/117/354
- Title:
- OB associations from Hipparcos
- Short Name:
- J/AJ/117/354
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A comprehensive census of the stellar content of the OB associations within 1 kpc from the Sun is presented, based on Hipparcos positions, proper motions, and parallaxes. It is a key part of a long-term project to study the formation, structure, and evolution of nearby young stellar groups and related star-forming regions. OB associations are unbound "moving groups", which can be detected kinematically because of their small internal velocity dispersion. The nearby associations have a large extent on the sky, which traditionally has limited astrometric membership determination to bright stars (V~<6mag), with spectral types earlier than ~B5. The Hipparcos measurements allow a major improvement in this situation. Moving groups are identified in the Hipparcos Catalog by combining de Bruijne's (1999MNRAS.306..394H) refurbished convergent point method with the "Spaghetti method" of Hoogerwerf & Aguilar (1999, MNRAS, in press). Astrometric members are listed for 12 young stellar groups, out to a distance of ~650pc. These are the three subgroups Upper Scorpius, Upper Centaurus Lupus, and Lower Centaurus Crux of Sco OB2, as well as Vel OB2, Tr 10, Col 121, Per OB2, {alpha} Persei (Per OB3), Cas-Tau, Lac OB1, Cep OB2, and a new group in Cepheus, designated as Cep OB6.
- ID:
- ivo://CDS.VizieR/J/A+A/371/497
- Title:
- OB associations in the spiral galaxy NGC 300
- Short Name:
- J/A+A/371/497
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of a search for OB associations in NGC 300. Using an automatic and objective method (PLC technique) 117 objects were found. Statistical tests indicate that our sample is contaminated by less than 10 detections due to random concentrations of blue stars. Spatial distributions of detected associations and H II regions are strongly correlated. The size distribution reveals a significant peak at about 60{mu}rad which corresponds to 125 parsecs if a distance modulus of 26.66mag is assumed. Besides the objects with sizes corresponding to typical associations we also found several much larger objects. A second level application of our detection method revealed that most of these are composed of smaller subgroups, with sizes of about 100pc.
- ID:
- ivo://CDS.VizieR/J/ApJS/2/389
- Title:
- Observations of O and B stars
- Short Name:
- J/ApJS/2/389
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This catalog of O and B stars contains magnitudes, colors, spectral types and polarization for 1259 stars. In addition to observations, the catalogue contains the derived absorption and distance modulus. A photoelectric photometer attached to the 82-inch (2m) reflector of the McDonald Observatory was used for the polarization observations. The photometric UBV observations were made over a period of 4 years with the 13-inch (33cm) and the 82-inch telescopes at McDonald. The spectroscopic classification was made with a new camera installed on the Cassegrain spectrograph, with a dispersion of 86{AA}/mm at H{delta}.
- ID:
- ivo://CDS.VizieR/J/ApJS/241/32
- Title:
- OB stars from the LAMOST DR5 spectra
- Short Name:
- J/ApJS/241/32
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 22901 OB spectra of 16032 stars identified from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope data release 5 (LAMOST DR5) data set. A larger sample of OB candidates are first selected from the distributions in the spectral line indices' space. Then, all 22901 OB spectra are identified by manual inspection. Based on a subsample validation, we find that the completeness of the OB spectra reaches about 89+/-22% for the stars with spectral types earlier than B7, while around 57+/-16% B8-B9 stars are identified. The smaller completeness for late B stars will lead to the difficulty in discriminating them from A0-A1-type stars. The subclasses of the OB samples are determined using the software package MKCLASS. With a careful validation using 646 subsamples, we find that MKCLASS can give fairly reliable subtypes and luminosity classes for most of the OB stars. The uncertainty of the spectral subtype is around 1 subtype, and the uncertainty of the luminosity class is around 1 level. However, about 40% of the OB stars fail to be assigned to any class by MKCLASS, and a few spectra are significantly misclassified by MKCLASS. This is likely because the template spectra of MKCLASS are selected from nearby stars in the solar neighborhood, while the OB stars in this work are mostly located in the outer disk and may have lower metallicities. The rotation of the OB stars may also be responsible for the misclassifications. Moreover, we find that the spectral and luminosity classes of the OB stars located in the Galactic latitude larger than 20{deg} are substantially different with those located in the latitude smaller than 20{deg}, which may either be due to the observational selection effect or may hint a different origin of the high Galactic latitude OB stars.
