The Cluster Palomar 1

An object whose APOGEE_TARGET1 value includes one or more of the bitmasks in the following table was targeted for spectroscopy as part of this ancillary target program. See SDSS-III bitmasks to learn how to use these values to identify objects in this ancillary target program.

Pal 1 is a faint, potentially young globular cluster that may be associated with the Monoceros Ring or Galactic Anti-center Stellar Stream (Rosenberg et al. 1998b; Crane et al. 2003), and whose spatial position, young age, and extended tidal tails (Niederste-Ostholt et al. 2010) make it a good candidate for a recently accreted object currently undergoing disruption by the Milky Way. This ancillary program is collecting the first large and homogeneous set of spectra in this red, faint, sparse cluster, with the goal of tightly constraining the cluster’s metallicity and exploring its potentially-unusual chemistry in many dimensions.

Matthew Shetrone, Jennifer Simmerer

The cluster targets were selected with a combination of 2MASS and SDSS photometry. The initial selection comprised 2MASS stars less than 90 arcmin from the cluster center that satisfied the following criteria:

• no neighboring object within 6 arcsec,
• 2MASS JHK_s photometric quality flags of “A” and all other contamination flags null, and
• 11 < H < 14.5 mag.

Then the sample was trimmed to those stars bracketed in (J-K_s) by isochrones at the most probable boundaries of the cluster age (5 to 12 Gyr) and metallicity ([Fe/H]=-1 to -0.5), assuming E(J-K_s)=0.112 and a distance modulus of 15.76 (Rosenberg et al. 1998a,b; Sarajedini et al. 2007; Harris 2010).
After all the 2MASS-selected candidates were matched with the SDSS DR7 photometric database (Abazajian et al. 2009), an additional cut in (u, g-r) space was performed. As the few existing ugr red giant branch isochrones are rather inconsistent in the possible age range of the cluster, stars along the probable giant branch locus were randomly selected, with even sampling between 0.5 < (g-r) < 1.6 mag. Also included are the three stars identified as cluster members by Rosenberg et al. (1998a).

Abazajian, K. N., Adelman-McCarthy, J. K., Agüeros, M. A., et al. 2009, ApJS, 182, 543
Crane, J., Majewski, S. R., Rocha-Pinto, H. J., et al. 2003, ApJ, 594, L119
Harris, W.E. 2010, arXiv:1012.3224
Niederste-Ostholt, et al. 2010, MNRAS:L, 408, L66
Rosenberg, A., Piotto, G., Saviane, I., Aparicio, A., & Gratton, R. 1998a, AJ, 115, 658
Rosenberg, A., Saviane, I., Piotto, G., Aparicio, A., & Zaggia, S. R. 1998b, AJ, 115, 648
Sarajedini, A., et al. 2007, AJ, 133, 1658