PROPERTIES OF THE OPEN CLUSTER TOMBAUGH 1 FROM HIGH-RESOLUTION SPECTROSCOPY AND uvbyCaHβ PHOTOMETRY*

Abstract

Open clusters can be the key to deepening our knowledge on various issues involving the structure and evolution of the Galactic disk and details of stellar evolution because a cluster's properties are applicable to all its members. However, the number of open clusters with detailed analysis from high-resolution spectroscopy or precision photometry imposes severe limitations on studies of these objects. To expand the number of open clusters with well-defined chemical abundances and fundamental parameters, we investigate the poorly studied, anticenter open cluster Tombaugh 1. Using precision uvbyCaHβ photometry and high-resolution spectroscopy, we derive the cluster's reddening, obtain photometric metallicity estimates, and, for the first time, present a detailed abundance analysis of 10 potential cluster stars (nine clump stars and one Cepheid). Using the radial position from the cluster center and multiple color indices, we have isolated a sample of unevolved, probable single-star members of Tombaugh 1. From 51 stars, the cluster reddening is found to be -.008, where the errors refer to the internal standard errors of the mean. The weighted photometric metallicity from m 1 and hk is [Fe/H]=−0.10±0.02, while a match to the Victoria-Regina Strömgren isochrones leads to an age of 0.95±0.10 Gyr and an apparent modulus of -m M ( )=13.10±0.10. Radial velocities identify six giants as probable cluster members, and the elemental abundances of Fe, Na, Mg, Al, Si, Ca, Ti, Cr, Ni, Y, Ba, Ce, and Nd have been derived for both the cluster and the field stars. Tombaugh 1 appears to be a typical inner thin disk, intermediate-age open cluster of slightly subsolar metallicity, located just beyond the solar circle, with solar elemental abundance ratios except for the heavy s-process elements, which are a factor of two above solar. Its metallicity is consistent with a steep metallicity gradient in the galactocentric region between 9.5 and 12 kpc. Our study also shows that Cepheid XZ CMa is not a member of Tombaugh 1 and reveals that this Cepheid presents signs of barium enrichment, making it a probable binary star.

Galactic Structure in the Outer Disk: The Field in the Line of Sight to the Intermediate-Age open Cluster Tombaugh 1*

“…During the nights of 2010 January 5, 6, 9, and 10, we observed 40stars of the field toward the open cluster Tombaugh1 (10 stars from boxes A and B, 11 stars from box C, and 9 stars from box D; see Figure 1) on Cerro Manqui at the Las Campanas Observatory using the Inamori-Magellan Areal Camera & Spectrograph (IMACS; Dressler et al 2006), attached to the 6.5 m Magellan Telescope. The 10 potential cluster stars of boxA were studied in Sales Silva et al (2016). For the stars of boxes A, B, and C, we used the multi-object echelle (MOE) spectroscopic mode, while the spectra of the box D stars were obtained using the multi-object mode with a grating of 600 lines/mm (G600-8.6).…”

The Origins of Young Stars in the Direction of the Leading Arm of the Magellanic Stream: Abundances, Kinematics, and Orbits*

“…Although CD14-A18 lies slightly below the metal-rich ZAMS, its v sin i of 65 ± 10 km•s −1 and super-solar abundance patterns suggest it is not an HB star. Moreover, if it is actually in the MS phase, from § 3.3, it is a metal-rich star located at R GC = 6.26 kpc, which agrees well with the Galactic radial metallicity gradient (e.g., Magrini et al 2009;Sales Silva et al 2016). Therefore, we mark this target as a MS star.…”

Triangulum–Andromeda Overdensity: a Region with a Complex Stellar Population

“…In Figure 2 we show for the target star 7 an example of the spectral syntheses and best fit abundances for the Ba II line (left panel) and the Eu II line (right panel). The atomic parameters of the iron-peak elements, as well as Na, Al and Ba were obtained from Heiter et al (2015), Sales Silva et al (2016 and McWilliam (1998), whereas for Eu we used the atomic parameters from M. Roriz et al (2019, in preparation). For Cr and Na we adopted the NLTE corrections from and Lind et al (2011), respectively.…”