The goal of ANCHORS is to provide a uniform (not necessarily optimal) database for the comparison of data from different clusters.

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American Astronomical Society, San Diego, January 2005
ANCHORS Poster - pdf - postscript
Protostars and Planets V articles, October 2005
Spitzbart, "An Archive of Chandra Observations of Regions of Star Formation (ANCHORS)" - pdf - postscript
Bizunok, "A Study of Stellar Flares in ANCHORS Star Cluster Database" pdf
Winston, "Spitzer and Chandra Observations of the Serpens Young Stellar Cluster" pdf
Six Years of Chandra Symposium, Cambridge, November 2005
ANCHORS Poster - pdf - postscript

Science background

The archive is designed to aid both the X-ray astronomer with a desire to compare X-ray datasets and the star formation astronomer wishing to compare stars across the spectrum. It brings together Chandra data on open clusters and other young stars.

From the earliest Einstein observations, it has been clear that young stars are bright, time--variable X-ray sources (Feigelson & Decampli 1981, Montmerle et al.1983). The source of the X-ray emission has been assigned to various physical mechanisms depending on the mass of the stars. These include (from high to low mass) wind-wind/ISM interactions, emission of an unseen companion, an alpha - Omega dynamo driven by the interaction of the stellar core with the convective envelope and rotation or an alpha - alpha or turbulent dynamo capable of producing emission without core-envelope shearing.

Though only a small fraction of the total luminosity of these stars, the X-ray flux is the main observable difference between young stars without disks and field stars. The high energy emission of the high mass stars not only leads to local shocks, but may also excite diffuse emission (Wolk et al.2002, Townsley et al.2003, Yusef-Zadeh et al.2001). Finally, X-rays induced ionization and melting undoubtably have significant effects within protoplanetary disks (Feigelson et al.2002).

Chandra has proven to be the perfect vehicle for the study of regions of star formation. Its superb spatial resolution allows Chandra to resolve stars in crowded regions 2-3 kpc away. With good sensitivity between 2 and 8 keV, Chandra can penetrate star forming clouds to levels rivaling near-IR telescopes. These features allow Chandra to investigate star formation which is more massive, more embedded and more distant than previously possible.

While much can be learned about stellar evolution from the study of individual clusters, science return is enhanced when the clusters are viewed as a group. As a pilot study, we examined brown dwarfs observed by Chandra during AO1-2. We found almost 70 candidate brown dwarfs had been detected by Chandra (Wolk 2003b) (though only 8 bone-fide). Trends indicate that the younger brown dwarfs are hotter in X-rays than the field brown dwarfs, but the total X-ray luminosity of detected brown dwarfs are similar. Another study of a subset of objects was done by Feigelson et al. (2002). They examined only the 43 X-ray sources in the ONC between 0.7 and 1.4 solar masses in order to understand the mean properties of the young Sun at 0.5 Gyr. They conclude that the flares which occur during the protoplanetary phase can cause significant production of unusual nuclieds including Al-26. Using the point source database, one could follow the progression of luminosity and variability for sun-like stars from the birthline to the present day (with the inclusion of AO-4 target NGC~752) without having to weigh the impact of the different analysis assumptions made by each team. Similar studies can be performed on intermediate mass stars. These studies are particularly interesting since flares imply the presence of confined plasmas which should be absent in these stars.

Figure 1. Examples of color-coded maps easily created from the point source catalog. Clockwise from upper left, scaling based on 50% quantile, absorption column (nH), source density (N/min^2), and temperature (kT).


References
Feigelson, E.D. & Decampli, W.M. 1981, ApJ 243, 89.
Feigelson, E.D., et al. 2002, ApJ 572, 335.
Townsley, L., et al. 2003, ApJ, 593, 874.
Wolk, S.J., et al. 2002, ApJ 580, L161.
Wolk, S.J. 2003, Brown Dwarfs E. Martin ed. p447.
Yusef-Zadeh, F., et al. 2002, ApJ 570, 665.


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