874 research outputs found
X-ray view of IC348 in the light of an updated cluster census
We study the properties of the coronae of the low-mass stars in the young
(~2-3Myr), nearby (~310pc) open cluster IC348 combining X-ray and
optical/infrared data. The four existing Chandra observations of IC348 are
merged, thus providing a deeper and spatially more complete X-ray view than
previous X-ray studies of the cluster. We have compiled a comprehensive catalog
of IC348 members taking into account recent updates to the cluster census. Our
data collection comprises fundamental stellar parameters, infrared excess
indicating the presence of disks, Halpha emission as a tracer of chromospheric
emission or accretion and mass accretion rates. We have detected 290 X-ray
sources in four merged Chandra exposures, of which 187 are associated with
known cluster members. Only four of the X-ray sources are brown dwarfs
(spectral type M6 and later). The detection rate is highest for diskless Class
III stars and increases with stellar mass. This may be explained with higher
X-ray luminosities for higher mass and later evolutionary stage that is evident
in the X-ray luminosity functions. In particular, we find that for the lowest
examined masses (0.1-0.25 Msun) there is a difference between the X-ray
luminosity functions of accreting and non-accreting stars (classified on the
basis of their Halpha emission strength) as well as those of disk-bearing and
diskless stars (classified on the basis of the slope of the spectral energy
distribution). These differences disappear for higher masses. This is related
to our finding that the L_x/L_bol ratio is non-constant across the
mass/luminosity sequence of IC348 with a decrease towards lower luminosity
stars. Our analysis of an analogous stellar sample in the Orion Nebula Cluster
suggests that the decline of L_x/L_ bol for young stars at the low-mass end of
the stellar sequence is likely universal.Comment: Accepted for publication in Astronomy & Astrophysic
Chandra X-ray observation of the young stellar cluster NGC 3293 in the Carina Nebula Complex
We characterize the stellar population of the poorly explored young stellar
cluster NGC 3293 at the northwestern periphery of the Carina Nebula Complex, in
order to evaluate the cluster age and the mass function, and to test claims of
an abnormal IMF and a deficit of M <= 2.5 M_sun stars. We performed a deep (70
ksec) X-ray observation of NGC 3293 with Chandra and detected 1026 individual
X-ray point sources. We identify counterparts for 74% of the X-ray sources in
deep near-infrared images. Our data clearly show that NGC 3293 hosts a large
population of solar-mass stars, refuting claims of a lack of M <= 2.5 M_sun
stars. The analysis of the color magnitude diagram suggests an age of ~8-10 Myr
for the low-mass population of the cluster. There are at least 511 X-ray
detected stars with color magnitude positions that are consistent with young
stellar members within 7 arcmin of the cluster center. The number ratio of
X-ray detected stars in the 1-2 M_sun range versus the M >= 5 M_sun stars
(known from optical spectroscopy) is consistent with the expectation from a
normal field initial mass function. Most of the early B-type stars and 20% of
the later B-type stars are detected as X-ray sources. Our data shows that NGC
3293 is one of the most populous stellar clusters in the entire Carina Nebula
Complex. The cluster probably harbored several O-type stars, whose supernova
explosions may have had an important impact on the early evolution of the
Carina Nebula Complex.Comment: accepted for Astronomy & Astrophysic
Using Narrow Band Photometry to Detect Young Brown Dwarfs in IC348
We report the discovery of a population of young brown dwarf candidates in
the open star cluster IC348 and the development of a new spectroscopic
classification technique using narrow band photometry. Observations were made
using FLITECAM, the First Light Camera for SOFIA, at the 3-m Shane Telescope at
Lick Observatory. FLITECAM is a new 1-5 micron camera with an 8 arcmin field of
view. Custom narrow band filters were developed to detect absorption features
of water vapor (at 1.495 microns) and methane (at 1.66 microns) characteristic
of brown dwarfs. These filters enable spectral classification of stars and
brown dwarfs without spectroscopy. FLITECAM's narrow and broadband photometry
was verified by examining the color-color and color-magnitude characteristics
of stars whose spectral type and reddening was known from previous surveys.
Using our narrow band filter photometry method, it was possible to identify an
object measured with a signal-to-noise ratio of 20 or better to within +/-3
spectral class subtypes for late-type stars. With this technique, very deep
images of the central region of IC348 (H ~ 20.0) have identified 18 sources as
possible L or T dwarf candidates. Out of these 18, we expect that between 3 - 6
of these objects are statistically likely to be background stars, with the
remainder being true low-mass members of the cluster. If confirmed as cluster
members then these are very low-mass objects (~5 Mjupiter). We also describe
how two additional narrow band filters can improve the contrast between M, L,
and T dwarfs as well as provide a means to determine the reddening of an
individual object.Comment: 43 pages, 17 figures. Accepted for publication in the Astrophysical
Journal 27 June 200
The onset of X-ray emission in young stellar objects: a Chandra observation of the Serpens star-forming region
AIMS: To study the properties of X-ray emissions from young stellar objects
(YSOs), through their evolution from Class I to Class III and determine whether
Class 0 protostars emit in X-rays. METHODS: A deep Chandra X-ray observation of
the Serpens star-forming region was obtained. The Serpens Cloud Core is ideally
suited for this type of investigation, being populated by a dense and extremely
young cluster whose members are found in all different evolutionary stages,
including six well studied Class 0 sources. RESULTS: None of the six Class 0
protostars is detected in our observations, excluding the presence of sources
with X-ray luminosities > 0.4 10^30 erg/s (for column densities of the order of
4 10^{23} cm^-2, or A_V ~ 200). A total of 85 X-ray sources are detected and
the light curves and spectra of 35 YSOs are derived. There is a clear trend of
decreasing absorbing column densities as one moves from Class I to Class III
sources, and, possibly, evidence of decreasing plasma temperatures, too. We
observe a strong, long-duration, flare from a Class II low-mass star, for which
we derive a flaring loop length of the order of 20 stellar radii. We interpret
the flaring event as originating from a magnetic flux tube connecting the star
to its circumstellar disk. The presence of such a disk is supported by the
detection, in the spectrum of this star, of 6.4 keV Fe fluorescent emission.Comment: Accepted for publication in A&
Evidence for Evolution Among Primordial Disks in the 5 Myr Old Upper Scorpius OB Association
Moderate-resolution, near-infrared spectra between 0.8 and 5.2 microns were
obtained for 12 late-type (K0-M3) disk-bearing members of the ~5 Myr old Upper
Scorpius OB association using SpeX on the NASA Infrared Telescope Facility. For
most sources, continuum excess emission first becomes apparent between ~2.2 and
4.5 microns and is consistent with that produced by single-temperature
blackbodies having characteristic temperatures ranging from ~500 to 1300 K. The
near-infrared spectra for 5 of 12 Upper Scorpius sources exhibit Pa-gamma,
Pa-beta and Br-gamma emission, indicators of disk accretion. Using a
correlation between Pa-beta and Br-gamma emission line luminosity and accretion
luminosity, mass accretion rates (Mdot) are derived for these sources that
range from Mdot = 3.5 X 10^{-10} to 1.5 X 10^{-8} MSun per yr. Merging the SpeX
observations with Spitzer Space Telescope mid-infrared (5.4-37.0 micron)
spectroscopy and 24 and 70 micron broadband photometry, the observed spectral
energy distributions are compared with those predicted by two-dimensional,
radiative transfer accretion disk models. Of the 9 Upper Scorpius sources
examined in this analysis, 3 exhibit spectral energy distributions that are
most consistent with models having inner disk radii that substantially exceed
their respective dust sublimation radii. The remaining Upper Scorpius members
possess spectral energy distributions that either show significant dispersion
among predicted inner disk radii or are best described by models having inner
disk rims coincident with the dust sublimation radius.Comment: 35 pages, 5 figures, accepted for publication in the Astronomical
Journa
Detection of an Inner Gaseous Component in a Herbig Be Star Accretion Disk: Near- and Mid-Infrared Spectrointerferometry and Radiative Transfer modeling of MWC 147
This is the author accepted manuscript. The final version is available from American Astronomical Society via the DOI in this record.We study the geometry and the physical conditions in the inner (AU-scale) circumstellar region around the young Herbig Be star MWC 147 using long-baseline spectrointerferometry in the near-infrared (NIR) K-band, VLTI/AMBER observations, and PTI archive data, as well as the mid-infrared (MIR) N-band, VLTI/MIDI observations. The emission from MWC 147 is clearly resolved and has a characteristic physical size of ~1.3 and ~9 AU at 2.2 and 11 μm, respectively (Gaussian diameter). The MIR emission reveals asymmetry consistent with a disk structure seen under intermediate inclination. The spectrally dispersed AMBER and MIDI interferograms both show a strong increase in the characteristic size toward longer wavelengths, much steeper than predicted by analytic disk models assuming power-law radial temperature distributions. We model the interferometric data and the spectral energy distribution of MWC 147 with two-dimensional, frequency-dependent radiation transfer simulations. This analysis shows that models of spherical envelopes or passive irradiated Keplerian disks (with vertical or curved puffed-up inner rim) can easily fit the SED, but predict much lower visibilities than observed; the angular size predicted by such models is 2-4 times larger than the size derived from the interferometric data, so these models can clearly be ruled out. Models of a Keplerian disk with optically thick gas emission from an active gaseous disk (inside the dust sublimation zone), however, yield a good fit of the SED and simultaneously reproduce the absolute level and the spectral dependence of the NIR and MIR visibilities. We conclude that the NIR continuum emission from MWC 147 is dominated by accretion luminosity emerging from an optically thick inner gaseous disk, while the MIR emission also contains contributions from the outer, irradiated dust disk.S. K. was
supported for this research through a fellowship from the International
Max Planck Research School ( IMPRS) for Radio and
Infrared Astronomy at the University of Bonn
Light-microscopy methods in C. elegans research
Ever since Caenorhabditis elegans was introduced as a model system it has been tightly linked to microscopy, which has led to significant advances in understanding biology over the last decades. Developing new technologies therefore is an essential part in the endeavor to gain further mechanistic insights into developmental biology. This review will discuss state-of-the-art developments in quantitative light microscopy in the context of C. elegans research as well as the impact these technologies have on the field. We will highlight future developments that currently promise to revolutionize biological research by combining sequencing-based single-cell technologies with high-resolution quantitative imaging
OpenSPIM - an open access platform for light sheet microscopy
Light sheet microscopy promises to revolutionize developmental biology by
enabling live in toto imaging of entire embryos with minimal phototoxicity. We
present detailed instructions for building a compact and customizable Selective
Plane Illumination Microscopy (SPIM) system. The integrated OpenSPIM hardware
and software platform is shared with the scientific community through a public
website, thereby making light sheet microscopy accessible for widespread use
and optimization to various applications.Comment: 7 pages, 3 figures, 6 supplementary videos, submitted to Nature
Methods, associated public website http://openspim.or
ImgLib2-generic image processing in Java
Summary: ImgLib2 is an open-source Java library for n-dimensional data representation and manipulation with focus on image processing. It aims at minimizing code duplication by cleanly separating pixel-algebra, data access and data representation in memory. Algorithms can be implemented for classes of pixel types and generic access patterns by which they become independent of the specific dimensionality, pixel type and data representation. ImgLib2 illustrates that an elegant high-level programming interface can be achieved without sacrificing performance. It provides efficient implementations of common data types, storage layouts and algorithms. It is the data model underlying ImageJ2, the KNIME Image Processing toolbox and an increasing number of Fiji-Plugins
Relative Evolutionary Time Scale of Hot Molecular Cores with Respect to Ultra Compact HII Regions
Using the Owens Valley and Nobeyama Radio Observatory interferometers, we
carried out an unbiased search for hot molecular cores and ultracompact UC HII
regions toward the high-mass star forming region G19.61--0.23. In addition, we
performed 1.2 mm imaging with SIMBA, and retrieved 3.5 and 2 cm images from the
VLA archive data base. The newly obtained 3 mm image brings information on a
cluster of high-mass (proto)stars located in the innermost and densest part of
the parsec scale clump detected in the 1.2 mm continuum. We identify a total of
10 high-mass young stellar objects: one hot core (HC) and 9 UC HII regions,
whose physical parameters are obtained from model fits to their continuum
spectra. The ratio between the current and expected final radii of the UC \HII
regions ranges from 0.3 to 0.9, which leaves the possibility that all O-B stars
formed simultaneously. Under the opposite assumption -- namely that star
formation occurred randomly -- we estimate that HC lifetime is less than
1/3 of that of UCHII regions on the basis of the source number ratio
between them.Comment: 13 pages, 2 figs, including a color fi
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