Stromgren and H  photometry of associations and open clusters - III. Cen OB1 and Cru OB1

Kaltcheva, N.; Георгиев, Л.

doi:10.1093/mnras/269.2.289

Cited by 20 publications

(26 citation statements)

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“…Balona (1992) claims that HD 101191 is an eclipsing binary with an orbital period of 2.084 days with a Strömgren b value of ∼6.56 out of eclipse. However, a later study by Kaltcheva & Georgiev (1994) gives b = 8.618. The photometric compilation of Hauck & Mermilliod (1998) reports b = 6.586 for the nearby variable star HD 101205 (V871 Cen) at 1.…”

Section: Cpd-59mentioning

confidence: 94%

Radial Velocities of Galactic O-Type Stars. I. Short-Term Constant Velocity Stars

Gies

Hillwig

McSwain

et al. 2011

The Astronomical Journal

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Section: Cpd-59mentioning

confidence: 94%

Radial Velocities of Galactic O-Type Stars. I. Short-Term Constant Velocity Stars

Gies

Hillwig

McSwain

et al. 2011

The Astronomical Journal

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“…The distance to the Cru OB1 association in Humphreys (1978) is 2400 pc; Kaltcheva & Georgiev (1994) estimate it to be 2730 pc. The interstellar Ca ii lines seen in the spectra of 10 stars in this association that are in our sample are shown in Fig.…”

Section: Comparison With Association Distancesmentioning

confidence: 95%

The interstellar Ca II distance scale

Megier

Strobel

Галазутдинов

et al. 2009

A&A

100

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Aims. We attempt to extend the relation between the strengths of the interstellar Ca ii lines and the distances to early-type stars to objects beyond 1 kiloparsec, with the line saturation taken into account.Methods. We measure the Ca ii K and Ca ii H equivalent widths, and compute Ca ii column densities for 262 lines of sight towards early-type stars with available Hipparcos parallaxes (π). The targets are located within a few hundred parsecs of the Galactic plane, and span all the range of Galactic longitudes. We fit the N Ca ii -parallax relation with a function of the form π = 1/(a · N Ca ii + b), using a maximum-likelihood approach to take account of errors in both variables. We use the resultant formula to estimate distances to stars in OB associations and clusters, and compare them to those found in the literature, usually estimated by spectrophotometric methods. 1.3, we obtain the following approximate formula for the distance: D Ca ii = 77 + (2.78 + Results. For lines of sight with EW(K)/EW(H) > EW(K) EW(H) −0.932 )EW(H), where the equivalent widths EW(K) and EW(H) are in mÅ, and the distance D Ca ii in parsecs.The errors in D Ca ii , resulting from the uncertainty in the fit parameters and errors in the equivalent widths, are typically about 15% of the distance. We can also expect the equation not to hold for objects situated farther than a few hundred parsecs from the Galactic plane. We find several cases of significant column density differences between association or cluster members, especially notable in the Trumpler 16 cluster, indicating either a local contribution to the Ca ii column density, or background/foreground stars being confused with members. The ratio D Ca ii /D assoc appears to depend on the Galactic longitude, being highest in the range 70 • < l < 120 • and lowest for 200 • < l < 300 • . This effect may be due to large-scale structure being present in the Ca ii layer, or to the nonmember confusion being enhanced in these directions.

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“…(A color version of this figure is available in the online journal.) association has been studied by different authors, with most recent values converging toward d = 2.3 kpc, though values up to d = 2.5 kpc are reported (Kaltcheva & Georgiev 1994;Humphreys 1978, and references therein). We will assume that LS 2883 is located at the distance to the association, even though values as high as 2.8 kpc seem compatible with the data available.…”

Section: Distance and Color Excess Estimatesmentioning

confidence: 99%

Astrophysical Parameters of Ls 2883 and Implications for the PSR B1259-63 Gamma-Ray Binary

Negueruela

Ribó

Herrero

et al. 2011

ApJ

127

174

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Only a few binary systems with compact objects display TeV emission. The physical properties of the companion stars represent basic input for understanding the physical mechanisms behind the particle acceleration, emission, and absorption processes in these so-called gamma-ray binaries. Here we present high-resolution and high signalto-noise optical spectra of LS 2883, the Be star forming a gamma-ray binary with the young non-accreting pulsar PSR B1259-63, showing it to rotate faster and be significantly earlier and more luminous than previously thought. Analysis of the interstellar lines suggests that the system is located at the same distance as (and thus is likely a member of) Cen OB1. Taking the distance to the association, d = 2.3 kpc, and a color excess of E(B − V ) = 0.85 for LS 2883 results in M V ≈ −4.4. Because of fast rotation, LS 2883 is oblate (R eq 9.7 R and R pole 8.1 R ) and presents a temperature gradient (T eq ≈ 27,500 K, log g eq = 3.7; T pole ≈ 34,000 K, log g pole = 4.1). If the star did not rotate, it would have parameters corresponding to a late O-type star. We estimate its luminosity at log(L * /L ) 4.79 and its mass at M * ≈ 30 M . The mass function then implies an inclination of the binary system i orb ≈ 23• , slightly smaller than previous estimates. We discuss the implications of these new astrophysical parameters of LS 2883 for the production of high-energy and very high-energy gamma rays in the PSR B1259-63/ LS 2883 gamma-ray binary system. In particular, the stellar properties are very important for prediction of the line-like bulk Comptonization component from the unshocked ultrarelativistic pulsar wind.

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Stromgren and H photometry of associations and open clusters - III. Cen OB1 and Cru OB1

Cited by 20 publications

References 0 publications

Radial Velocities of Galactic O-Type Stars. I. Short-Term Constant Velocity Stars

Radial Velocities of Galactic O-Type Stars. I. Short-Term Constant Velocity Stars

The interstellar Ca II distance scale

Astrophysical Parameters of Ls 2883 and Implications for the PSR B1259-63 Gamma-Ray Binary

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