New Red Jewels in Coma Berenices

Abstract

We have used Sloan Digital Sky Survey-III (SDSS-III) Apache Point Observatory Galactic Evolution Experiment (APOGEE) radial velocity observations in the near-infrared H-band to explore the membership of the nearby (86.7 ± 0.9 pc) open cluster Coma Berenices (Melotte 111), concentrating on the poorly-populated low-mass end of the main sequence. Using SDSS-III APOGEE radial velocity measurements, we confirm the membership of eight K/M dwarf members, providing the first confirmed low-mass members of the Coma Berenices cluster. Using R ∼ 2000 spectra from IRTF-SpeX, we confirm the independently luminosity classes of these targets, and find their metallicities to be consistent with the known solar mean metallicity of Coma Berenices and of M dwarfs in the Solar neighborhood. In addition, the APOGEE spectra have enabled measurement of v sin i for each target and detection for the first time of the low-mass secondary components of the known binary systems Melotte 111 102 and Melotte 111 120, as well as identification of the previously unknown binary system 2MASS J12214070+2707510. Finally, we use Kilodegree Extremely Little Telescope (KELT) photometry to measure photometric variability and rotation periods for a subset of the Coma Berenices members.

The evolution of surface magnetic fields in young solar-type stars II: the early main sequence (250–650 Myr)★

“…Collier Cameron et al (2009) found photometric rotation periods of 9.26 days in 2007 and 4.79 days in 2004, and concluded that the shorter period is an alias of the longer period, due to an unfortunate spot distribution. Terrien et al (2014) found a photometric period of 9.483±0.028 days, which is approximately consistent with the value of Collier Cameron et al (2009). Both values are roughly consistent with our period measurements from the longitudinal field and from ZDI, therefore we adopt the value of 9.483 ± 0.028 days, since it is based on more observations obtained over a longer time period.…”

“…Periodograms based on the longitudinal magnetic field measurements from the April run yield best periods around 9 days (first order χ 2 ν = 3.8, second order χ 2 ν = 1.3), as do the measurements from the June run (first order χ 2 ν = 4.2, second order χ 2 ν = 1.0), however both data sets require a second order fit to produce an acceptable χ 2 . Using the full dataset produces a best period of 9.4 days, favoring the period from Terrien et al (2014) (first order χ 2 ν = 4.5, second order χ 2 ν = 3.6). There appears to be moderate but significant differences between the April and June B l curves (Fig.…”

In-Sync I: Homogeneous Stellar Parameters From High-Resolution Apogee Spectra for Thousands of Pre-Main Sequence Stars

“…On the other hand in the Pleiades we measure radial velocities systematically higher by 400 ± 60 m s −1 than the radial velocities measured for the same stars with CORAVEL (Mermilliod et al 2009). The latter offset is consistent at the 2 sigma level with the radial velocity offset of 602 ± 116 m s −1 found between APOGEE and CORAVEL radial velocities for stars in Coma Ber (Terrien et al 2014). We decided not to calibrate our radial velocities to either one of these systems, because of the different directions of the systematic offsets with respect to the radial-velocity standards from Prato (2007) and Mermilliod et al (2009).…”

The Apache Point Observatory Galactic Evolution Experiment (APOGEE)

“…In fact, the APOGEE instrument and the existing radial velocity software routinely deliver radial velocities at a precision of ∼0.07 km s −1 for S/N>20, while the survey provides external calibration sufficient to ensure accuracies at the level of ∼0.35 km s −1 (Nidever et al 2015; Section 7.3)-a level of performance that allows more subtle dynamical effects to be measured. For example, the detection of pattern speeds of-or kinematical substructure in the disk due to perturbations and resonances from-spiral arms, the bar, or other (e.g., dark matter) substructure (e.g., Dehnen 1998;Famaey et al 2005;Junqueira et al 2015), the detection of stellar binary companions (e.g., Terrien et al 2014), the assessment of stellar membership in star clusters (e.g., Terrien et al 2014;Carlberg et al 2015) or extended stellar kinematic groups (i.e., "moving groups" or "superclusters") in the disk (e.g., Eggen 1958Eggen , 1998Montes et al 2001;Malo et al 2013), and the accurate measurement of stellar velocity dispersions in star clusters or satellite galaxies (Majewski et al 2013) are all made possible with radial velocity measurements of the rms precision and external accuracies routinely achieved by APOGEE for main survey program stars. Nevertheless, it has been shown that even greater precision and accuracy may be obtained from APOGEE spectra, which increases the sensitivity to even lower mass stellar companions (Deshpande et al 2013) and greatly benefits the exploration of the intricate dynamics of young star clusters (Cottaar et al 2014;Foster et al 2015).…”