Search

Start Over Subject ob stars Content Level Research
101. Walraven photometry of OB stars
ID:
ivo://CDS.VizieR/J/A+A/369/527
Title:
Walraven photometry of OB stars
Short Name:
J/A+A/369/527
Date:
21 Oct 2021
Publisher:
CDS
Description:
About 700 stars, mostly OB-stars, were observed by the author at the former Leiden Southern Station at Hartebees poortdam, South Africa, in the observing seasons 1965, 1968, 1969, 1974, 1977, 1978. Observations were made in the five channels of the Walraven photometric system. Due to weathering of the telescope mirror the W channel gave no reliable results for the faintest stars (m=11mag); in these cases the U-W colour index is not given. The change in sensitivity in the V channel, supposedly having occurred in 1968, was not recognised. For a description of the Walraven VBLUW photometric system, see e.g. <GCPD/11>
102. Walraven photometry of OB stars
ID:
ivo://CDS.VizieR/J/A+AS/137/113
Title:
Walraven photometry of OB stars
Short Name:
J/A+AS/137/113
Date:
21 Oct 2021
Publisher:
CDS
Description:
Observations of OB-stars, made in 1959 and 1960 at the Leiden Southern Station near Hartebeespoortdam, South Africa, with the VBLUW photometer attached to th e 90 cm light-collector, are given in this paper. They are compared with photome try obtained by Graham (1968BANS....2..397G), Walraven & Walraven (1977BAN....15...67W), Lub & Pel (1977A&A....54..137L) and van Genderen et al. (1984A&AS...58..537V). Formulae for the transformation of the present observations to those of Walraven & Walraven (1977BAN....15...67W) and Lub & Pel (1977A&A....54..137L) are given. For a description of the VBLUW photometric system, see e.g. <GCPD/11>
103. W51 OB stars NIR spectroscopy
ID:
ivo://CDS.VizieR/J/A+A/624/A63
Title:
W51 OB stars NIR spectroscopy
Short Name:
J/A+A/624/A63
Date:
21 Oct 2021
Publisher:
CDS
Description:
The interplay between the formation of stars, stellar feedback and cloud properties strongly influences the star formation history of giant molecular clouds. The formation of massive stars leads to a variety of stellar clusters, ranging from low stellar density OB associations to dense, gravitationally bound starburst clusters. We aimed at identifying the massive stellar content and reconstructing the star formation history of the W51 giant molecular cloud. We performed near-infrared imaging and K-band spectroscopy of the massive stars in W51. We analysed the stellar populations using colour-magnitude and colour-colour diagrams and compared the properties of the spectroscopically identified stars with stellar evolution models. We derive the ages of the different sub-clusters in W51 and, based on our spectroscopy derive an age for W51 of 3Myrs or less. The age of the P Cygni star LS1 and the presence of two still forming proto- clusters suggests that the star formation history of W51 is more complex than a single burst. We did not find evidence for triggered star formation and we concluded that the star formation in W51 is multi seeded. We finally concluded that W51 is a OB association where different sub-clusters form over a time span of at least 3-5Myrs.
104. XMM view of NGC 6231: OB stars
ID:
ivo://CDS.VizieR/J/MNRAS/372/661
Title:
XMM view of NGC 6231: OB stars
Short Name:
J/MNRAS/372/661
Date:
21 Oct 2021
Publisher:
CDS
Description:
In this second paper of the series, we focus on the X-ray properties of the OB star population of NGC 6231. As a tool for our analysis, we performed a literature-based census of the OB stars in the field of view. More than one hundred objects are found, among which 30% can be associated with an X-ray source. All the O-type stars are detected in the X-ray domain as soft and reasonably strong emitters. [...] Among B-type stars, the detection rate is only about 25% in the sub-type range B0-B4 and remains mostly uniform throughout the different sub-populations while it drops significantly at later sub-types. The associated X-ray spectra are harder than those of O-type stars. Our analysis points towards the emission being rather associated with a physical (in a multiple system) PMS companion. However, we still observe a correlation between the bolometric luminosity of the B stars and the measured X-ray luminosity. [...]
105. XMM view of NGC 6231 open cluster
ID:
ivo://CDS.VizieR/J/A+A/454/1047
Title:
XMM view of NGC 6231 open cluster
Short Name:
J/A+A/454/1047
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of an X-ray campaign towards the young open cluster NGC 6231. The XMM-Newton observations, of a total duration of about 180 ks, reveals that NGC 6231 is very rich in the X-ray domain too. Indeed, 610 X-ray sources are detected in the present field of view, centered on the cluster core. The limiting sensitivity of our survey is approximately 610^-15^erg/s/cm^2^ but clearly depends on the location in the field of view and on the source spectrum. Using different existing catalogues, over 85% of the X-ray sources could be associated with at least one optical and/or infrared counterpart within a limited cross-correlation radius of 2.5 or 3-arcsec according to the optical/IR catalogue used. The surface density distribution of the X-ray sources presents a slight N-S elongation. Once corrected for the spatial sensitivity variation of the EPIC instruments, the radial profile of the source surface density is well described by a King profile with a central density of about 8 sources per arcmin^2^ and a core radius close to 3.1-arcmin. The distribution of the X-ray sources seems closely related to the optical source distribution. The expected number of foreground and background sources should represent about 9% of the detected sources, thus strongly suggesting that most of the observed X-ray emitters are physically belonging to NGC 6231. Finally, beside a few bright but soft objects -- corresponding to the early-type stars of the cluster -- most of the sources are relatively faint (~5x10^-15^erg/s/cm^2^) with an energy distribution peaked around 1.0-2.0keV.
106. X-ray emission from Galactic stellar bow shocks
ID:
ivo://CDS.VizieR/J/AJ/157/176
Title:
X-ray emission from Galactic stellar bow shocks
Short Name:
J/AJ/157/176
Date:
03 Nov 2021 07:20:14
Publisher:
CDS
Description:
We present a stacking analysis of 2.61 Ms of archival Chandra observations of stellar wind bow shocks. We place an upper limit on the X-ray luminosity of infrared-detected bow shocks of <2x10^29^ erg/s, a more stringent constraint than has been found in previous archival studies and dedicated observing campaigns of nearby bow shocks. We compare the X-ray luminosities and L_X_/L_bol_ ratios of bow shock driving stars to those of other OB stars within the Chandra field of view. Driving stars are, on average, of later spectral type than the field-of-view OB stars, and we do not observe any unambiguously high L_X_/L_bol_ ratios indicative of magnetic stars in our sample. We additionally assess the feasibility of detecting X-rays from stellar wind bow shocks with the proposed Lynx X-ray Observatory. If the X-ray flux originating from the bow shocks is just below our Chandra detection limit, the nearest bow shock in our sample (at ~0.4 kpc with an absorbing column of ~10^21^/cm^2^) should be observable with Lynx in exposure times on the order of ~100 ks.
107. X-ray properties of O and B stars in Carina
ID:
ivo://CDS.VizieR/J/ApJS/194/7
Title:
X-ray properties of O and B stars in Carina
Short Name:
J/ApJS/194/7
Date:
21 Oct 2021
Publisher:
CDS
Description:
The key empirical property of the X-ray emission from O stars is a strong correlation between the bolometric and X-ray luminosities. In the framework of the Chandra Carina Complex Project, 129 O and B stars have been detected as X-ray sources; 78 of those, all with spectral type earlier than B3, have enough counts for at least a rough X-ray spectral characterization. This leads to an estimate of the L_X-L_BOL ratio for an exceptional number of 60 O stars belonging to the same region and triples the number of Carina massive stars studied spectroscopically in X-rays. The derived log(L_X/L_BOL) is 7.26 for single objects, with a dispersion of only 0.21dex. Using the properties of hot massive stars listed in the literature, we compare the X-ray luminosities of different types of objects. In the case of O stars, the L_X-L_BOL ratios are similar for bright and faint objects, as well as for stars of different luminosity classes or spectral types. Binaries appear only slightly harder and slightly more luminous in X-rays than single objects; the differences are not formally significant (at the 1% level), except for the L_X-L_BOL ratio in the medium (1.0-2.5keV) energy band. Weak-wind objects have similar X-ray luminosities but they display slightly softer spectra compared with "normal" O stars with the same bolometric luminosity. Discarding three overluminous objects, we find a very shallow trend of harder emission in brighter objects. The properties of the few B stars bright enough to yield some spectral information appear to be different overall (constant X-ray luminosities, harder spectra), hinting that another mechanism for producing X-rays, besides wind shocks, might be at work. However, it must be stressed that the earliest and X-ray brightest among these few detected objects are similar to the latest O stars, suggesting a possibly smooth transition between the two processes.

Limit your search