ancillary science program



NEW! IN-SYNC paper III on IC348 dynamics

IN-SYNC III: The Dynamical State of IC348 - A Super-virial Velocity Dispersion and a Puzzling Sign of Convergence

      M. Cottaar, K. R. Covey, J. B. Foster, M. R. Meyer, J. C. Tan, D. L. Nidever, S. D. Chojnowski, N. Da Rio, K. M. Flaherty, P. M. Frinchaboy, S. Majewski, M. F. Skrutskie, J. C. Wilson, and G. Zasowski - ApJ, accepted.

Most field stars will have encountered the highest stellar density and hence the largest number of interactions in their birth environment. Yet the stellar dynamics during this crucial phase are poorly understood. Here we analyze the radial velocities measured for 152 out of 380 observed stars in the 2-6 Myr old star cluster IC 348 as part of the SDSS-III APOGEE. The radial velocity distribution of these stars is fitted with one or two Gaussians, convolved with the measurement uncertainties including binary orbital motions. Including a second Gaussian improves the fit; the high-velocity outliers that are best fit by this second component may either (1) be contaminants from the nearby Perseus OB2 association, (2) be a halo of ejected or dispersing stars from IC 348, or (3) reflect that IC 348 has not relaxed to a Gaussian velocity distribution. We measure a velocity dispersion for IC 348 of 0:72\pm0:07 km/s (or 0:64\pm0:08 km/s if two Gaussians are fitted), which implies a supervirial state, unless the gas contributes more to the gravitational potential than expected. No evidence is found for a dependence of this velocity dispersion on distance from the cluster center or stellar mass. We also find that stars with lower extinction (in the front of the cloud) tend to be redshifted compared with stars with somewhat higher extinction (towards the back of the cloud). This data suggests that the stars in IC 348 are converging along the line of sight. We show that this correlation between radial velocity and extinction is unlikely to be spuriously caused by the small cluster rotation of 0:024\pm0:013 km/s/arcmin or by correlations between the radial velocities of neighboring stars. This signature, if confirmed, will be the first detection of line-of-sight convergence in a star cluster. Possible scenarios for reconciling this convergence with IC 348's observed supervirial state include: a) the cluster is fluctuating around a new virial equilibrium after a recent disruption due to gas expulsion or a merger event, or b) the population we identify as IC 348 results from the chance alignment of two sub-clusters converging along the line of sight. Additional measurements of tangential and radial velocities in IC 348 will be important for clarifying the dynamics of this region, and informing models of the formation and evolution of star clusters. The radial velocities analyzed in this paper have been made available online.

README On-line data

  • Radial velocities


IN-SYNC paper II on NGC1333

IN-SYNC II: Virial Stars from Sub-Virial Cores -- The Velocity Dispersion of Embedded Pre-Main-Sequence Stars in NGC 1333

      J. B. Foster, M. Cottaar, K. R. Covey, H. G. Arce, M. R. Meyer, D. L. Nidever, K. G. Stassun, J. C. Tan, S. D. Chojnowski, N. Da Rio, K. M. Flaherty, L. Rebull, P. M. Frinchaboy, S. R. Majewski, M. Skrutskie, J. C. Wilson, G. Zasowski - ApJ accepted.

The initial velocity dispersion of newborn stars is a major unconstrained aspect of star formation theory. Using near-infrared spectra obtained with the APOGEE spectrograph, we show that the velocity dispersion of young (1-2 Myr) stars in NGC 1333 is 0.92+/-0.12 km/s after correcting for measurement uncertainties and the effect of binaries. This velocity dispersion is consistent with the virial velocity of the region and the diffuse gas velocity dispersion, but significantly larger than the velocity dispersion of the dense, star-forming cores, which have a sub-virial velocity dispersion of 0.5 km/s. Since the NGC 1333 cluster is dynamically young and deeply embedded, this measurement provides a strong constraint on the initial velocity dispersion of newly-formed stars. We propose that the difference in velocity dispersion between stars and dense cores may be due to the influence of a 70 micro-Gauss magnetic field acting on the dense cores, or be the signature of a cluster with initial sub-structure undergoing global collapse.

IN-SYNC paper I on data analysis in IC348

IN-SYNC I: Homogeneous stellar parameters from high resolution APOGEE spectra for thousands of PMS stars

      M. Cottaar, K. R. Covey, M. R. Meyer, D. L. Nidever, K. G. Stassun, J. B. Foster, J. C. Tan, S. D. Chojnowski, N. Da Rio, K. M. Flaherty, S. Majewski, M. F. Skrutskie and G. Zasowski - ApJ, 794, 125

Over two years 8,859 high-resolution H-band spectra of 3,493 young (1 - 10 Myr) stars were gathered by the multi-object spectrograph APOGEE as part of the IN-SYNC ancillary program of the SDSS-III survey. Here we present the forward modelling approach used to derive effective temperatures, surface gravities, radial velocities, rotational velocities, and H-band veiling from these near-infrared spectra. We discuss in detail the statistical /and/ systematic uncertainties in these stellar parameters. In addition we present accurate extinctions by measuring the E(J-H) of these young stars with respect to a single-star photometric locus in the Pleiades. Finally we show a stellar radius spread of about 25% for late-type stars in IC 348 using three (nearly) independent measures of stellar radius, namely the extinction corrected luminosity, the surface gravity, and the Rsin i from the rotational velocities and literature rotation periods. Tables providing the spectral and photometric parameters for the Pleiades and IC 348 have been provided online.

README On-line data

  • Readme file

  • For individual epochs

  • For individual stars


The Perseus Cloud: target selection in IC348 and NGC1333

IC348 NGC1333

A total of XXXX stars have been targeted for high resolution spectroscopy in Perseus. Below we show the spatial distribution of the targets in the central regions of IC348 and NGC1333, overplotted to color-composite 2MASS JHKs image.

Radial velocity distribution

RV distribution

Histogram of eliocentric measured radial velocities in the Perseus molecular cloud. The blue line represents blah blah.

Double-lined spectroscopic binaries in IC348

Spectroscopic binaries

2 pre-main sequence double-lined spectroscopic binaries have been discovered in IC348. The image shows their spectra changing with epoch (in days).