458 research outputs found
A Catalog of Point Sources Towards NGC 1333
I present a catalog of point source objects towards NGC 1333, resolving a
wide variety of confusion about source names (and occasionally positions) in
the literature. I incorporate data from optical to radio wavelengths, but focus
most of the effort on being complete and accurate from J (1.25 um) to 24 um.
The catalog encompasses 52 deg<RA<52.5 deg and 31 deg<Dec<31.6 deg.
Cross-identifications include those from more than 25 papers and catalogs from
1994-2014, primarily those in wide use as origins of nomenclature. Gaps in our
knowledge are identified, with the most important being a lack of spectroscopy
for spectral types or even confirmation of youth and/or cluster membership. I
fit a slope to the spectral energy distribution (SED) between 2 and 24 um for
the members (and candidate members) to obtain an SED classification, and
compare the resulting classes to those for the same sources in the literature,
and for an SED fit between 2 and 8 um. While there are certainly differences,
for the majority of the sources, there is good agreement.Comment: 34 pages, 7 figures. Accepted to AJ. Table 2 and 3 will be published
in the journal, and are currently available upon request to the autho
Circumstellar Disks in the Outer Galaxy: the Star-Forming Region NGC 1893
It is still debated whether star formation process depends on environment. In
particular it is yet unclear whether star formation in the outer Galaxy, where
the environmental conditions are, theoretically, less conducive, occurs in the
same way as in the inner Galaxy. We investigate the population of NGC1893, a
young cluster ~3-4 Myr in the outer part of the Galaxy (galactic radius >11
Kpc), to explore the effects of environmental conditions on star forming
regions. We present infrared observations acquired using the IRAC camera
onboard the Spitzer Space Telescope and analyze the color-color diagrams to
establish the membership of stars with excesses. We also merge this information
with that obtained from Chandra ACIS-I observations, to identify the Class III
population. We find that the cluster is very rich, with 242 PMS Classical
T-Tauri stars and 7 Class 0/I stars. We identify 110 Class III candidate
cluster members in the ACIS-I field of view. We estimate a disk fraction for
NGC1893 of about 67%, similar to fractions calculated for nearby star forming
regions of the same age. Although environmental conditions are unfavorable,
star formation can clearly be very successful in the outer Galaxy, allowing
creation of a very rich cluster like NGC1893.Comment: 10 pages,7 figures,4 table
New Young Star Candidates in CG4 and Sa101
The CG4 and Sa101 regions together cover a region of ~0.5 square degree in
the vicinity of a "cometary globule" that is part of the Gum Nebula. There are
seven previously identified young stars in this region; we have searched for
new young stars using mid- and far-infrared data (3.6 to 70 microns) from the
Spitzer Space Telescope, combined with ground-based optical data and
near-infrared data from the Two-Micron All-Sky Survey (2MASS). We find infrared
excesses in all 6 of the previously identified young stars in our maps, and we
identify 16 more candidate young stars based on apparent infrared excesses.
Most (73%) of the new young stars are Class II objects. There is a tighter
grouping of young stars and young star candidates in the Sa101 region, in
contrast to the CG4 region, where there are fewer young stars and young star
candidates, and they are more dispersed. Few likely young objects are found in
the "fingers" of the dust being disturbed by the ionization front from the
heart of the Gum Nebula.Comment: Accepted for publication in A
B- and A-Type Stars in the Taurus-Auriga Star Forming Region
We describe the results of a search for early-type stars associated with the
Taurus-Auriga molecular cloud complex, a diffuse nearby star-forming region
noted as lacking young stars of intermediate and high mass. We investigate
several sets of possible O, B and early A spectral class members. The first is
a group of stars for which mid-infrared images show bright nebulae, all of
which can be associated with stars of spectral type B. The second group
consists of early-type stars compiled from (i) literature listings in SIMBAD;
(ii) B stars with infrared excesses selected from the Spitzer Space Telescope
survey of the Taurus cloud; (iii) magnitude- and color-selected point sources
from the 2MASS; and (iv) spectroscopically identified early-type stars from the
SDSS coverage of the Taurus region. We evaluated stars for membership in the
Taurus-Auriga star formation region based on criteria involving: spectroscopic
and parallactic distances, proper motions and radial velocities, and infrared
excesses or line emission indicative of stellar youth. For selected objects, we
also model the scattered and emitted radiation from reflection nebulosity and
compare the results with the observed spectral energy distributions to further
test the plausibility of physical association of the B stars with the Taurus
cloud. This investigation newly identifies as probable Taurus members three
B-type stars: HR 1445 (HD 28929), tau Tau (HD 29763), 72 Tau (HD 28149), and
two A-type stars: HD 31305 and HD 26212, thus doubling the number of stars A5
or earlier associated with the Taurus clouds. Several additional early-type
sources including HD 29659 and HD 283815 meet some, but not all, of the
membership criteria and therefore are plausible, though not secure, members.Comment: 31 pages, 18 figures, 6 tables. Accepted for publication in The
Astrophysical Journa
Rotation of Late-Type Stars in Praesepe with K2
We have Fourier analyzed 941 K2 light curves of likely members of Praesepe,
measuring periods for 86% and increasing the number of rotation periods (P) by
nearly a factor of four. The distribution of P vs. (V-K), a mass proxy, has
three different regimes: (V-K)<1.3, where the rotation rate rapidly slows as
mass decreases; 1.3<(V-K)<4.5, where the rotation rate slows more gradually as
mass decreases; and (V-K)>4.5, where the rotation rate rapidly increases as
mass decreases. In this last regime, there is a bimodal distribution of
periods, with few between 2 and 10 days. We interpret this to mean
that once M stars start to slow down, they do so rapidly. The K2 period-color
distribution in Praesepe (790 Myr) is much different than in the Pleiades
(125 Myr) for late F, G, K, and early-M stars; the overall distribution
moves to longer periods, and is better described by 2 line segments. For mid-M
stars, the relationship has similarly broad scatter, and is steeper in
Praesepe. The diversity of lightcurves and of periodogram types is similar in
the two clusters; about a quarter of the periodic stars in both clusters have
multiple significant periods. Multi-periodic stars dominate among the higher
masses, starting at a bluer color in Praesepe ((V-K)1.5) than in the
Pleiades ((V-K)2.6). In Praesepe, there are relatively more light curves
that have two widely separated periods, 6 days. Some of these could
be examples of M star binaries where one star has spun down but the other has
not.Comment: Accepted by Ap
CSI 2264: Simultaneous optical and X-ray variability in pre-Main Sequence stars. I: Time resolved X-ray spectral analysis during optical dips and accretion bursts in stars with disks
Pre-main sequence stars are variable sources. In stars with disks, this
variability is related to the morphology of the inner circumstellar region
(<0.1 AU) and that of the photosphere and corona, all impossible to be
spatially resolved with present day techniques. This has been the main
motivation for the Coordinated Synoptic Investigation of NGC 2264. In this
paper, we focus on the stars with disks. We analyze the X-ray spectral
properties extracted during optical bursts and dips in order to unveil the
nature of these phenomena. We analyze simultaneous CoRoT and Chandra/ACIS-I
observations to search for coherent optical and X-ray flux variability in stars
with disks. Then, stars are analyzed in two different samples. In stars with
variable extinction, we look for a simultaneous increase of optical extinction
and X-ray absorption during the optical dips; in stars with accretion bursts,
we search for soft X-ray emission and increasing X-ray absorption during the
bursts. Results. We find evidence for coherent optical and X-ray flux
variability among the stars with variable extinction. In 9/24 stars with
optical dips, we observe a simultaneous increase of X-ray absorption and
optical extinction. In seven dips, it is possible to calculate the NH/AV ratio
in order to infer the composition of the obscuring material. In 5/20 stars with
optical accretion bursts, we observe increasing soft X-ray emission during the
bursts that we associate to the emission of accreting gas. It is not surprising
that these properties are not observed in all the stars with dips and bursts,
since favorable geometric configurations are required. The observed variable
absorption during the dips is mainly due to dust-free material in accretion
streams. In stars with accretion bursts, we observe on average a larger soft
X-ray spectral component not observed in non accreting stars.Comment: Accepted for publication by Astronomy & Astrophysic
Wide-field Infrared Survey Explorer Observations of the Evolution of Massive Star-forming Regions
We present the results of a mid-infrared survey of 11 outer Galaxy massive star-forming regions and 3 open clusters with data from the Wide-field Infrared Survey Explorer (WISE). Using a newly developed photometric scheme to identify young stellar objects and exclude extragalactic contamination, we have studied the distribution of young stars within each region. These data tend to support the hypothesis that latter generations may be triggered by the interaction of winds and radiation from the first burst of massive star formation with the molecular cloud material leftover from that earlier generation of stars. We dub this process the "fireworks hypothesis" since star formation by this mechanism would proceed rapidly and resemble a burst of fireworks. We have also analyzed small cutout WISE images of the structures around the edges of these massive star-forming regions. We observe large (1-3 pc size) pillar and trunk-like structures of diffuse emission nebulosity tracing excited polycyclic aromatic hydrocarbon molecules and small dust grains at the perimeter of the massive star-forming regions. These structures contain small clusters of emerging Class I and Class II sources, but some are forming only a single to a few new stars
Rotation of Low-mass Stars in Taurus with K2
We present an analysis of K2 light curves (LCs) from Campaigns 4 and 13 for members of the young (~3 Myr) Taurus association, in addition to an older (~30 Myr) population of stars that is largely in the foreground of the Taurus molecular clouds. Out of 156 of the highest-confidence Taurus members, we find that 81% are periodic. Our sample of young foreground stars is biased and incomplete, but nearly all stars (37/38) are periodic. The overall distribution of rotation rates as a function of color (a proxy for mass) is similar to that found in other clusters: the slowest rotators are among the early M spectral types, with faster rotation toward both earlier FGK and later M types. The relationship between period and color/mass exhibited by older clusters such as the Pleiades is already in place by Taurus age. The foreground population has very few stars but is consistent with the USco and Pleiades period distributions. As found in other young clusters, stars with disks rotate on average slower, and few with disks are found rotating faster than ~2 days. The overall amplitude of the LCs decreases with age, and higher-mass stars have generally lower amplitudes than lower-mass stars. Stars with disks have on average larger amplitudes than stars without disks, though the physical mechanisms driving the variability and the resulting LC morphologies are also different between these two classes
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