P. A. Cargile et al. 2009 The Astronomical Journal 137 3230 doi:10.1088/0004-6256/137/2/3230
P. A. Cargile1, D. J. James1,2 and I. Platais3
Show affiliationsWe perform a new analysis of the extant ROSAT and XMM-Newton X-ray surveys of the southern open cluster Blanco 1, utilizing new BVIc photometric and proper motion data sets. In our study, we match optical counterparts to 47 X-ray sources associated with Blanco 1 cluster members, six of which were listed in previous X-ray studies as cluster nonmembers. Our new catalog of optical counterparts to X-ray sources clearly traces out the Blanco 1 main sequence in a color-magnitude diagram, extending from early G to mid-M spectral types. Additionally, we derive new X-ray luminosities as well as ratios of X-ray to bolometric luminosities for confirmed cluster members. We compare these X-ray properties to other young open clusters, including the coeval Pleiades cluster, to investigate the relationship between age and X-ray activity. We find that stars in Blanco 1 generally exhibit X-ray properties similar to those of other open clusters, namely increasing Lx /L bol with reducing mass for earlier-type stars, and a saturation limit of Lx /L bol at a magnitude of 10–3 for stars with V – Ic
1.25. More generally, the X-ray detected stars in Blanco 1 have X-ray emission magnitudes that agree with the overall trends seen in the other young clusters. We observe that X-ray emission decays as a function of age and the rate of this decay is mass dependent. Specifically, for higher mass stars, the trend is Skumanich like (i.e., Lx /L bol
age–1/2); however, as one goes to lower masses the magnitude of X-ray emission becomes less of a function of age. In fact, for the lowest mass stars (M-type), there is no observable reduction in X-ray production during the first ~1 Gyr of their lives. However, due to a lack of sensitivity to low X-ray fluxes, there may exist M-type stars that have less than saturated levels of X-ray flux which are not included in our study. In a direct comparison of Blanco 1 to the Pleiades open cluster, members of both clusters have similar X-ray characteristics; however, there does appear to be some discrepancies in the distribution of Lx /L bol as a function of color that may be related to scatter seen in the Pleiades CMD. Moreover, previous comparisons of this nature for Blanco 1 were not possible due to the reliance on photographic photometry. This is where the power of precise, homogeneous, and standardized CCD photometry allows for a high fidelity, detailed study of the X-ray properties of stars in Blanco 1, as well as a thorough comparison of Blanco 1 to other well-studied open clusters.
open clusters and associations: general; open clusters and associations: individual (Blanco 1); stars: activity; stars: evolution; X-rays: stars
Issue 2 (2009 February)
Received 2008 July 9, accepted for publication 2008 November 13
Published 2009 January 28
P. A. Cargile et al. 2009 The Astronomical Journal 137 3230
A B Balantekin and S Kuyucak 1997 J. Phys. G: Nucl. Part. Phys. 23 1159
Michael Flohr and Annekathrin Müller-Lohmann J. Stat. Mech. (2005) P12004
S Poggi et al 2006 J. Phys.: Conf. Ser. 32 198
Owen Madden and Simon F Ross 2005 Class. Quantum Grav. 22 515
M A Black 1972 Phys. Educ. 7 515