L-band data of 30 Doradus at 3.5 micron taken with SPIREX (South Pole Infrared Explorer) is presented. The photometry was combined with 2MASS (<II/246>) JHK data at 1.25 -2.2 micron. Colour-colour and colour-magnitude diagrams are constructed and used to determine the sources with infrared excess. These are interpreted as circumstellar disks, and enable the fraction of sources with disks (the cluster disk fraction or CDF) to be determined. We find that ~42% of the sources detected at L-band in 30 Doradus have an IR-excess.
Near infrared imaging observations in JHK broad bands and H_2_ v=1-0 S(1) narrow band of the star formation region GGD12-15 are presented in this article. The images reveal young compact infrared clusters and infrared nebulae in association with infrared sources, as well as outflow activities characterized by H_2_ emission knots. Most of the infrared point sources are invisible in the optical wave band. The JHK' photometric results of 76 infrared point sources contain 32 with infrared excess, and 5 with the characteristics of protostars, indicating very active star formation activities in the molecular clouds.
We report the results of a deep near-infrared (JHK) survey of the outer parts of the Trapezium Cluster with Gemini South/Flamingos. 396 sources were detected in a 26-arcmin^2^ area, including 138 brown dwarf candidates, defined as M<0.075M_{sun}_ for an assumed age of 1Myr. Only 33 of the brown dwarf candidates are planetary mass candidates with estimated masses in the range 0.003<M<0.012M_{sun}_. In an extinction-limited sample (AV<5) complete to approximately 0.005M_{sun}_ (5M_Jup_) the mass function appears to drop by a factor of 2 at the deuterium burning threshold, i.e. at planetary masses. After allowing for background contamination it is likely that planetary mass objects at 3-13M_Jup_ number <10% of the cluster population, with an upper limit of 13%. Analysis of the spatial distribution of stars and brown dwarf candidates suggests that brown dwarfs and very low-mass stars (M<0.1M_{sun}_) are less likely than more massive stars to have wide (>150AU) binary companions.
To study how the structure of the envelopes of young stellar objects (YSOs) evolve, we carried out a deep JHK'-band imaging survey of the M17 star-forming region using a near-infrared camera and the Infrared Camera and Spectrograph with adaptive optics mounted on the Subaru Telescope. In this survey, we found 51 dark silhouettes against bright near-infrared nebula emissions as background lights. They are regarded as envelopes associated with YSOs due to their size and association with the YSOs. We derived size, morphology, extinction, and mass for each silhouette envelope.
Using UKIRT on Mauna Kea, we have carried out a new near-infrared J, H, K monitoring survey of almost a square degree of the star-forming Orion Nebula Cluster with observations on 120 nights over three observing seasons, spanning a total of 894 days. We monitored ~15000 stars down to J~20 using the WFCAM instrument, and have extracted 1203 significantly variable stars from our data. By studying variability in young stellar objects (YSOs) in the H-K, K color-magnitude diagram, we are able to distinguish between physical mechanisms of variability. Many variables show color behavior indicating either dust-extinction or disk/accretion activity, but we find that when monitored for longer periods of time, a number of stars shift between these two variability mechanisms. Further, we show that the intrinsic timescale of disk/accretion variability in young stars is longer than that of dust-extinction variability. We confirm that variability amplitude is statistically correlated with evolutionary class in all bands and colors. Our investigations of these 1203 variables have revealed 73 periodic AA Tau type variables, many large-amplitude and long-period (P>15 days) YSOs, including three stars showing widely spaced periodic brightening events consistent with circumbinary disk activity, and four new eclipsing binaries. These phenomena and others indicate the activity of long-term disk/accretion variability processes taking place in young stars. We have made the light curves and associated data for these 1203 variables available online.
We investigate three embedded massive star-forming regions using the Near-Infrared Imager (NIRIM) camera on the 3.5m WIYN telescope. We report J-, H-, and K'-band photometry in the clusters AFGL437, AFGL5180, and AFGL5142, and use these results to probe the stellar populations, extinction, and ages of the clusters.
We present near-IR (NIR) J, H, and Ks images and K-band spectroscopy of two newly discovered stellar clusters at different stages of evolution. Our spectra suggest the presence of massive young stellar objects in the heavily embedded cluster in the star-forming region near radio source G353.4-0.4 and an O5-O6V star in the cluster near radio source G305+00.2.
We present J, H, and Ks photometry of the Orion Nebula Cluster (ONC) obtained at the CTIO/Blanco 4m telescope at Cerro Tololo with the Infrared Side Port Imager camera. From the observations we have assembled a catalog of about ~7800 sources distributed over an area of approximately 30'x40', the largest of any survey deeper than the Two Micron All Sky Survey (2MASS) in this region. The catalog provides absolute coordinates accurate to about 0.15-arcsec and 3{sigma} photometry in the 2MASS system down to J~=19.5mag, H~=18.0mag, Ks~=18.5mag, enough to detect planetary size objects 1Myr old under A_V_~=10mag of extinction at the distance of the Orion Nebula.
We have used the Two Micron All Sky Survey and Palomar Observatory Sky Survey photographic plates, digitized by the US Naval Observatory's Precision Measuring Machine program, to derive proper motions over a 100 square degree, spatially complete region centered on the Praesepe open cluster. Proper-motion measurements spanned the magnitude range R~12-19, which covers most of the lower main sequence in Praesepe. The incidence of H{alpha} emission from moderate-resolution (~2600), red spectroscopy of 434 faint candidate members and 126 field control stars demonstrates that ~60%-80% of candidates within 2{deg} of the cluster center are genuine Praesepe members.
