Intrinsic colour indices of OB supergiants, giants and dwarfs in the UBVRIJHKLM System

Wegner, W.

doi:10.1093/mnras/270.2.229

Cited by 231 publications

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“…To determine the distances of the compact Galactic X-ray sources of our sample, for CVs we assumed an absolute magnitude M V ∼ 9 and an intrinsic color index (V − R) 0 ∼ 0 mag (Warner 1995), whereas for high-mass X-ray binaries (HMXBs), when applicable, we used the intrinsic stellar color indices and absolute magnitudes reported in Lang (1992) and Wegner (1994). For the single low-mass X-ray binary (LMXB) in our sample, we considered (V − R) 0 ∼ 0 ∼ M R (e.g., van Paradijs & McClintock 1995).…”

Section: Resultsmentioning

confidence: 99%

Unveiling the nature ofINTEGRALobjects through optical spectroscopy

Masetti¹,

Parisi

Palazzi³

et al. 2010

A&A

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Hard X-ray surveys performed by the INTEGRAL satellite have discovered a conspicuous fraction (up to 30%) of unidentified objects among the detected sources. Here we continue our program of identification of these objects by (i) selecting probable optical candidates by means of positional cross-correlation of the INTEGRAL detections with soft X-ray, radio, and/or optical archives and (ii) performing optical spectroscopy on them. As a result, we pinpointed and identified, or more accurately characterized, 44 definite or likely counterparts of INTEGRAL sources. Among them, 32 are active galactic nuclei (AGNs; 18 with broad emission lines, 13 with narrow emission lines only, and one X-ray bright, optically normal galaxy) with redshift 0.019 < z < 0.6058, 6 cataclysmic variables (CVs), 5 high-mass X-ray binaries (2 of which in the Small Magellanic Cloud), and 1 low-mass X-ray binary. This was achieved by using 7 telescopes of various sizes and archival data from two online spectroscopic surveys. The main physical parameters of these hard X-ray sources were also determined using the multiwavelength information available in the literature. In general, AGNs are the most abundant population among hard X-ray objects, and our results confirm the tendency of finding AGNs more frequently than any other type of hard X-ray emitting object among unidentified INTEGRAL sources when optical spectroscopy is used as an identification tool. Moreover, the deeper sensitivity of the more recent INTEGRAL surveys enables one to begin detecting hard X-ray emission above 20 keV from sources such as LINER-type AGNs and non-magnetic CVs.

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Section: Resultsmentioning

confidence: 99%

Unveiling the nature ofINTEGRALobjects through optical spectroscopy

Masetti¹,

Parisi

Palazzi³

et al. 2010

A&A

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“…Many investigations (e.g. Wegner 1994;Whittet & vanBreda 1980;Rieke & Lebofsky 1985) There are four main methods for determining the extinction and the extinction law in a given direction:…”

Section: Extinction Lawmentioning

confidence: 99%

“…5.2) are also overplotted (filled triangles). The small thick segment on the bottom left of the plots is the locus of the unreddened O-B3 stars (from Martins et al 2006;Koornneef et al 1983;and Wegner 1994). a color variation smaller than 0.1 mag (De Grijs et al 2001) and an age variation can be represented as isochrones parallel to the reddening vector in color−color diagrams (Leitherer 1999). The most likely explanation is the mis-association with near-infrared data.…”

Section: Extinction Lawmentioning

confidence: 99%

Statistical study of OB stars in NGC 6334 and NGC 6357

Russeil

Zavagno

Adami

et al. 2012

A&A

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Context. Star-forming complexes are large structures exhibiting massive star-formation at different stages of evolution, from dense cores to well-developed H ii regions. They are very interesting for the study of the formation and evolution of stars. NGC 6334 and NGC 6357 are two active and relatively nearby star-forming complexes. From the extinction map and the sub-mm cold dust emission, and because they have similar velocities, these regions are most likely connected. However, located in the direction of the Galactic center their radial velocity is not representative of their distance. An alternative is then to determine the distance of NGC 6334 and NGC 6357 from their stellar content. Aims. Our aim is to perform a census of O-B3 ionising stars in NGC 6334 and NGC 6357, to determine the extinction coefficient, and the distance of both regions. A census of O-B3 stars is an essential basis for estimating the statistical lifetime of the earliest massive star-forming phases. Methods. We performed a U, B, V, and R photometric survey of a large area covering NGC 6334 and NGC 6357 with the VIMOS (ESO-VLT) and the MOSAIC (CTIO) instruments. This allows us to have a complete census of O to B3 stars up to V = 22.6 mag. The OB stars are selected based on their U − B and B − V colors. The most robust extinction coefficient is determined from color−color plots before computing the distance of the OB stars. Results. We find a higher value than typical of the diffuse interstellar medium for R V of 3.53 ± 0.08 and 3.56 ± 0.15 for NGC 6357 and NGC 6334, respectively. Adopting these R V values, the distances of NGC 6357 and NGC 6334 are 1.9 ± 0.4 kpc and 1.7 ± 0.3 kpc. We conclude that, within the error bars, both regions are thus at the same distance of 1.75 kpc (weighted mean). We confirm that the value of R V is linked to the large dust grain content. In particular, we found that there are more very small grains in NGC 6357 than in NGC 6334, suggesting that NGC 6357 could be more evolved than NGC 6334. Placed in the Galactic context, the NGC 6334-NGC 6357 complex appears to be located at the inner edge of the Sagittarius-Carina arm. Our census of O to B3 stars leads to a count of ∼230, which allows us to determine the statistical lifetime of the earliest phases of the massive stars. The starless and the protostellar phases have a mean statistical lifetime of ∼1.5 × 10 4 yr and ∼2.2 × 10 5 yr, respectively.

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“…accounting for: i) a conservative maximum color excess error, σE(B − V), of 0.04 mag; ii) a root-mean-square deviation of the observation at .55 μm, σ V , of 0.01 mag (Savage et al 1985); iii) a root-mean-square deviation of the photometric observation at wavelength λ r , σ m λr , ranging from 0.001−0.218 mag (Wesselius et al 1982) in the UV range and given by the 2MASS catalog in the IR one; and iv) classification errors and errors in the intrinsic colors, i.e, σ r,m , as given in Table 1B of Meyer & Savage (1981) in the UV range and derived from Wegner (1994) in the IR one. For each line of sight, the residual differences at the five UV wavelengths between the observed data and the best-fit standard CCM curve, as in Eq.…”

Section: The Samplementioning

confidence: 99%

Dust properties along anomalous extinction sightlines

Mazzei

Barbaro

2011

A&A

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Context. Studies of the dust extinction in the Galaxy have found that the large majority of sight lines analyzed obey a simple relation depending on one parameter, the total-to-selective extinction coefficient, R V . Different values of R V are able to match the whole extinction curve in different environments, thus characterize normal extinction curves. However anomalous curves i.e, curves which deviate strongly from this simple behavior have been observed in the Galaxy as well as external galaxies. Aims. More than sixty curves with large ultraviolet deviations from their best-fit one-parameter curve are analyzed. The extinction curves are fitted with dust models to shed light on the properties of the grains along selected lines of sight, the processes affecting them, and their relations with the environmental characteristics. Methods. The extinction curve models are developed using the latest prescriptions for grain-size distributions capable of describing one-parameter curves for R V values from 3.1 to 5.5. These models, extended here down to R V = 2.0, allow us to compare the resulting properties of our deviating curves with those of normal curves in a self-consistent framework, and thus to recover the relative trends overcoming the modeling uncertainties.Results. In addition to 20 anomalous curves extracted from the same sample for study in a previous paper and revised here to account for the latest updates, these curves represent the largest, homogeneous sample of anomalous curves studied so far with dust models. Our results show that the ultraviolet deviations are driven by a larger amount of small grains than predicted for lines of sight where extinction depends on only one parameter. Moreover, the dust-to-gas ratios of anomalous curves are lower than the same values for no deviating lines of sight. Conclusions. Both shocks and grain-grain collisions should destroy dust grains, hence reduce the amount of the dust trapped in the grains, modify the size distribution of the dust, and increase the small-to-large grain size ratio. Therefore, the extinction properties derived should correspond to sight lines where shocks and high velocity flows perturb the physical state of the interstellar medium and leave their signature on the dust properties.

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Intrinsic colour indices of OB supergiants, giants and dwarfs in the UBVRIJHKLM System

Cited by 231 publications

References 0 publications

Unveiling the nature ofINTEGRALobjects through optical spectroscopy

Unveiling the nature ofINTEGRALobjects through optical spectroscopy

Statistical study of OB stars in NGC 6334 and NGC 6357

Dust properties along anomalous extinction sightlines

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