10 research outputs found
The Brightening of Re50N: Accretion Event or Dust Clearing?
The luminous Class I protostar HBC 494, embedded in the Orion A cloud, is
associated with a pair of reflection nebulae, Re50 and Re50N, which appeared
sometime between 1955 and 1979. We have found that a dramatic brightening of
Re50N has taken place sometime between 2006 and 2014. This could result if the
embedded source is undergoing a FUor eruption. However, the near-infrared
spectrum shows a featureless very red continuum, in contrast to the strong CO
bandhead absorption displayed by FUors. Such heavy veiling, and the high
luminosity of the protostar, is indicative of strong accretion but seemingly
not in the manner of typical FUors. We favor the alternative explanation that
the major brightening of Re50N and the simultaneous fading of Re50 is caused by
curtains of obscuring material that cast patterns of illumination and shadows
across the surface of the molecular cloud. This is likely occurring as an
outflow cavity surrounding the embedded protostar breaks through to the surface
of the molecular cloud. Several Herbig-Haro objects are found in the region.Comment: 8 pages, accepted by Ap
A Database of 2MASS Near-Infrared Colors of Magellanic Cloud Star Clusters
The (rest-frame) near-IR domain contains important stellar population
diagnostics and is often used to estimate masses of galaxies at low as well as
high redshifts. However, many stellar population models are still relatively
poorly calibrated in this part of the spectrum. To allow an improvement of this
calibration we present a new database of integrated near-infrared JHKs
magnitudes for 75 star clusters in the Magellanic Clouds, using the 2-Micron
All-Sky Survey (2MASS). The majority of the clusters in our sample have robust
age and metallicity estimates from color-magnitude diagrams available in the
literature, and populate a range of ages from 10 Myr to 15 Gyr and a range in
[Fe/H] from -2.17 to +0.01 dex. A comparison with matched star clusters in the
2MASS Extended Source Catalog (XSC) reveals that the XSC only provides a good
fit to the unresolved component of the cluster stellar population. We also
compare our results with the often-cited single-channel JHK photometry of
Persson and collaborators, and find significant differences, especially for
their 30"-diameter apertures up to ~2.5 mag in the K-band, more than 1 mag in
J-K, and up to 0.5 mag in H-K. Using simulations to center apertures based on
maximum light throughput (as performed by Persson et al, we show that these
differences can be attributed to near-IR-bright cluster stars (e.g., Carbon
stars) located away from the true center of the star clusters. The wide age and
metallicity coverage of our integrated JHKs photometry sample constitutes a
fundamental dataset for testing population synthesis model predictions, and for
direct comparison with near-IR observations of distant stellar populations.Comment: AJ August 2006 issue, 67 pages, 8 tables, 17 figure