اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدInitial Results from The Spitzer Young Stellar Cluster Survey
333
0
0.0
(
0
)
تأليف
S. T. Megeath
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We report initial results from IRAC observations of four young stellar clusters. These regions are part of a larger Spitzer survey of 31 young stellar groups and clusters within 1 kpc of the Sun. In each of the four clusters, there are between 39 and 85 objects with colors inconsistent with reddened stellar photospheres. We identify these objects as young stars with significant emission from circumstellar dust. Applying an analysis developed in a companion paper (Allen et al. 2004), we classify these objects as either pre-main sequence stars with disks (class II) or protostellar objects (class I). These show that the sites of recent star formation are distributed over multi-parsec size scales. In two clusters, Cepheus C and S140, we find protostars embedded in filamentary dark clouds seen against diffuse emission in the IRAC bands.
قيم البحث
اقرأ أيضاً
We present first results from the Palomar Adaptive Optics Survey of Young Stars conducted at the Hale 5 m telescope. Through direct imaging we have discovered a brown dwarf and two low-mass stellar companions to the young solar-type stars HD 49197, H
D 129333 (EK Dra), and V522 Per, and confirmed a previously suspected companion to RX J0329.1+0118 (Sterzik et al. 1997), at respective separations of 0.95 (43 AU), 0.74 (25 AU), 2.09 (400 AU), and 3.78 (380 AU). Physical association of each binary system is established through common proper motion and/or low-resolution infrared spectroscopy. Based on the companion spectral types, we estimate their masses at 0.06, 0.20, 0.13, and 0.20 Msun, respectively. From analysis of our imaging data combined with archival radial velocity data, we find that the spatially resolved companion to HD 129333 is potentially identical to the previously identified spectroscopic companion to this star (Duquennoy & Mayor 1991). However, a discrepancy with the absolute magnitude suggests that the two companions could also be distinct, with the resolved one being the outermost component of a triple system. The brown dwarf HD 49197B is a new member of a growing list of directly imaged sub-stellar companions at 10-1000 AU separations from main sequence stars, indicating that such brown dwarfs may be more common than initially speculated.
Near Earth Objects (NEOs) are small Solar System bodies whose orbits bring them close to the Earths orbit. We are carrying out a Warm Spitzer Cycle 11 Exploration Science program entitled NEOSurvey --- a fast and efficient flux-limited survey of 597
known NEOs in which we derive diameter and albedo for each target. The vast majority of our targets are too faint to be observed by NEOWISE, though a small sample has been or will be observed by both observatories, which allows for a cross-check of our mutual results. Our primary goal is to create a large and uniform catalog of NEO properties. We present here the first results from this new program: fluxes and derived diameters and albedos for 80 NEOs, together with a description of the overall program and approach, including several updates to our thermal model. The largest source of error in our diameter and albedo solutions, which derive from our single band thermal emission measurements, is uncertainty in eta, the beaming parameter used in our thermal modeling; for albedos, improvements in Solar System absolute magnitudes would also help significantly. All data and derived diameters and albedos from this entire program are being posted on a publicly accessible webpage at nearearthobjects.nau.edu .
Context. Bulge globular clusters (BGCs) are exceptional tracers of the formation and chemodynamical evolution of this oldest Galactic component. However, until now, observational difficulties have prevented us from taking full advantage of these powe
rful Galactic archeological tools. Aims. CAPOS, the bulge Cluster APOgee Survey, addresses this key topic by observing a large number of BGCs, most of which have only been poorly studied previously. Even their most basic parameters, such as metallicity, [{alpha}/Fe], and radial velocity, are generally very uncertain. We aim to obtain accurate mean values for these parameters, as well as abundances for a number of other elements, and explore multiple populations. In this first paper, we describe the CAPOS project and present initial results for seven BGCs. Methods. CAPOS uses the APOGEE-2S spectrograph observing in the H band to penetrate obscuring dust toward the bulge. For this initial paper, we use abundances derived from ASPCAP, the APOGEE pipeline. Results. We derive mean [Fe/H] values of $-$0.85$pm$0.04 (Terzan 2), $-$1.40$pm$0.05 (Terzan 4), $-$1.20$pm$0.10 (HP 1), $-$1.40$pm$0.07 (Terzan 9), $-$1.07$pm$0.09 (Djorg 2), $-$1.06$pm$0.06 (NGC 6540), and $-$1.11$pm$0.04 (NGC 6642) from three to ten stars per cluster. We determine mean abundances for eleven other elements plus the mean [$alpha$/Fe] and radial velocity. CAPOS clusters significantly increase the sample of well-studied Main Bulge globular clusters (GCs) and also extend them to lower metallicity. We reinforce the finding that Main Bulge and Main Disk GCs, formed in situ, have [Si/Fe] abundances slightly higher than their accreted counterparts at the same metallicity. We investigate multiple populations and find our clusters generally follow the light-element (anti)correlation trends of previous studies of GCs of similar metallicity. We finally explore the abundances ...
A new, unbiased Spitzer-MIPS imaging survey (~1.8 square degs) of the young stellar content of the Vela Molecular Cloud-D is presented. The survey is complete down to 5mJy and 250mJy at 24micron (mu) and 70mu, respectively. 849 sources are detected a
t 24mu and 52 of them also have a 70mu counterpart. The VMR-D region is one that we have already partially mapped in dust and gas millimeter emission, and we discuss the correlation between the Spitzer compact sources and the mm contours. About half of the 24mu sources are located inside the region delimited by the 12CO(1-0) contours (corresponding to only one third of the full area mapped with MIPS) with a consequent density increase of about 100% of the 24mu sources [four times for 70mu ones] moving from outside to inside the CO contours. About 400 sources have a 2MASS counterpart. So we have constructed a Ks vs. Ks-[24] diagram and identified the protostellar population. We find an excess of Class I sources in VMR-D in comparison with other star forming regions. This result is reasonably biased by the sensitivity limits, or, alternatively, may reflect a very short lifetime (<=10^6yr) of the protostellar content in this cloud. The MIPS images have identified embedded cool objects in most of the previously identified starless cores; in addition, there are 6 very young, possibly Class 0 objects identified. Finally we report finding of the driving sources for a set of five out of six very compact protostellar jets previously discovered in near-infrared images.
General results from a 3-5 micron spectroscopic survey of nearby low-mass young stellar objects are presented. L and M-band spectra have been obtained of ~50 low mass embedded young stars using the ISAAC spectrometer mounted on UT1-Antu at Paranal Ob
servatory. For the first time, a consistent census of the CO, H2O ices and the minor ice species CH3OH and OCN- and warm CO gas present around young stars is obtained, using large number statistics and resolving powers of up to R=10000. The molecular structure of circumstellar CO ices, the depletion of gaseous CO onto grains in protoplanetary disks, the presence of hot gas in the inner parts of circumstellar disks and in outflows and infalls are studied. Furthermore, the importance of scattering effects for the interpretation of the spectra have been addressed.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
