72 research outputs found
On the Chromaticity of the (NEO)WISE Astrometry
The Wide-field Infrared Survey Explorer (WISE, Wright et al. 2010) and its
follow-up Near-Earth Object (NEO) mission (NEOWISE, Mainzer et al. 2011) scan
the mid-infrared sky twice a year. The spatial and temporal coverage of the
resulting database is of utmost importance for variability studies, in
particular of young stellar objects (YSOs) which have red colors.
During such an effort, I noticed subarcsecond position offsets between
subsequent visits. The offsets do not appear for targets with small
colors, which points to a chromatic origin in the optics, caused by the
spacecraft pointing alternating ``forward'' and ``backward'' from one visit to
another. It amounts to 0\farcs1 for targets with .
Consideration of this chromatic offset will improve astrometry. This is of
particular importance for NEOs that are generally red.Comment: 3 pages, 1 figure, submitted to RNAA
A survey for variable young stars with small telescopes: III. Warm spots on the active star V1598Cyg
Magnetic spots on low-mass stars can be traced and characterised using multi-band photometric light curves. Here we analyse an extensive data set for one active star, V1598Cyg, a known variable K dwarf which is either pre-main sequence and/or in a close binary system. Our light curve contains 2854 photometric data points, mostly in V, Rc, Ic, but also in U, B and Hα, with a total baseline of about 4yr, obtained with small telescopes as part of the HOYS project. We find that V1598Cyg is a very fast rotator with a period of 0.8246 days and varying amplitudes in all filters, best explained as a signature of strong magnetic activity and spots. We fit the photometric amplitudes in V, Rc, Ic and use them to estimate spot properties, using a grid-based method that is also propagating uncertainties. We verify the method on a partial data set with high cadence and all five broad-band filters. The method yields spot temperatures and fractional spot coverage with typical uncertainties of 100K and 3-4%, respectively. V1598Cyg consistently exhibits spots that are a few hundred degrees warmer than the photosphere, most likely indicating that the light curve is dominated by chromospheric plage. The spot activity varies over our observing baseline, with a typical time scale of 0.5-1yr, which we interpret as the typical spot lifetime. Combining our light curve with archival data, we find a six year cycle in the average brightness, that is probably a sign of a magnetic activity cycle
Synergy of multifrequency studies from observations of NGC6334I
We combine multifrequency observations from the millimeter to near infrared
wavelengths that demonstrate the spatial distributions of H2, CO, and NH3
emission, which are all manifestations of various shocks driven by outflows of
deeply embedded sources in NGC6334I. In addition to the well-known
northeast-southwest outflow we detect at least one more outflow in the region
by combining observations from APEX, ATCA, SMA, Spitzer and VLT/ISAAC.
Potential driving sources will be discussed. NGC6334I exhibits several signs of
active star formation and will be a major target for future observatories such
as Herschel and ALMA.Comment: 6 pages, 6 figures, appeared in the proceedings of the workshop 'The
Universe Under The Microscope - Astrophysics At High Angular Resolution', see
http://www.iop.org/EJ/toc/1742-6596/131/
Infrared Observation of Hot Cores
We report on mid-infrared imaging of hot cores performed with SpectroCam-10
and TIMMI2. The observations aimed at the detection of thermal emission
presumably associated with the hot cores. Mid-infrared flux measurements are
required to improve the luminosity and optical depth estimates for these
sources. Results are presented for W3(HO), G9.62+0.19, G10.47+0.03, and the
possible hot core candidate G232.620+0.996. They illustrate that the morphology
of these sources cannot be described by simple geometries. Therefore,
line-of-sight effects and considerable extinction even at mid-infrared
wavelengths must not be neglected.Comment: 6 pages, 4 figures, Conference proceeding "Origins of stars and
planets: The VLT view", ESO, Garching, April 24-27 200
A survey for variable young stars with small telescopes: V - Analysis of TXOri, V505Ori, and V510Ori, the HST ULLYSES targets in the σOri cluster
Investigations of the formation of young stellar objects (YSOs) and planets require the detailed analysis of individual sources as well as statistical analysis of a larger number of objects. The Hubble UV Legacy Library of Young Stars as Essential Standards (ULLYSES) project provides such a unique opportunity by establishing a UV spectroscopic library of young high- and low-mass stars in the local universe. Here we analyse optical photometry of the three ULLYSES targets (TX Ori, V505 Ori, V510 Ori) and other YSOs in the σ Ori cluster taken at the time of the HST observations to provide a reference for those spectra. We identify three populations of YSOs along the line of sight to σ Ori, separated in parallax and proper motion space. The ULLYSES targets show typical YSO behaviour with pronounced variability and mass accretion rates of the order of 10−8 M⊙/yr. Optical colours do not agree with standard interstellar reddening and suggest a significant contribution of scattered light. They are also amongst the most variable and strongest accretors in the cluster. V505 Ori shows variability with a seven day period, indicating an inner disk warp at the co-rotation radius. Uncovering the exact nature of the ULLYSES targets will require improved detailed modelling of the HST spectra in the context of the available photometry, including scattered light contributions as well as non-standard reddening
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