1,406 research outputs found
Interferometry of chemically peculiar stars: theoretical predictions vs. modern observing facilities
By means of numerical experiments we explore the application of
interferometry to the detection and characterization of abundance spots in
chemically peculiar (CP) stars using the brightest star eps~Uma as a case
study. We find that the best spectral regions to search for spots and stellar
rotation signatures are in the visual domain. The spots can clearly be detected
already at a first visibility lobe and their signatures can be uniquely
disentangled from that of rotation. The spots and rotation signatures can also
be detected in NIR at low spectral resolution but baselines longer than 180~m
are needed for all potential CP candidates. According to our simulations, an
instrument like VEGA (or its successor e.g., FRIEND) should be able to detect,
in the visual, the effect of spots and spots+rotation, provided that the
instrument is able to measure , and/or closure phase. In
infrared, an instrument like AMBER but with longer baselines than the ones
available so far would be able to measure rotation and spots. Our study
provides necessary details about strategies of spot detection and the
requirements for modern and planned interferometric facilities essential for CP
star research.Comment: Accepted by NMRAS, 18 pages, 11 figures, 2 table
Surveying the Agents of Galaxy Evolution in the Tidally Stripped, Low Metallicity Small Magellanic Cloud (SAGE-SMC). I. Overview
The Small Magellanic Cloud (SMC) provides a unique laboratory for the study of the lifecycle of dust given its low metallicity (~1/5 solar) and relative proximity (~60 kpc). This motivated the SAGE-SMC (Surveying the Agents of Galaxy Evolution in the Tidally Stripped, Low Metallicity Small Magellanic Cloud) Spitzer Legacy program with the specific goals of studying the amount and type of dust in the present interstellar medium, the sources of dust in the winds of evolved stars, and how much dust is consumed in star formation. This program mapped the full SMC (30 deg^2) including the body, wing, and tail in seven bands from 3.6 to 160 μm using IRAC and MIPS on the Spitzer Space Telescope. The data were reduced and mosaicked, and the point sources were measured using customized routines specific for large surveys. We have made the resulting mosaics and point-source catalogs available to the community. The infrared colors of the SMC are compared to those of other nearby galaxies and the 8 μm/24 μm ratio is somewhat lower than the average and the 70 μm/160 μm ratio is somewhat higher than the average. The global infrared spectral energy distribution (SED) shows that the SMC has approximately 1/3 the aromatic emission/polycyclic aromatic hydrocarbon abundance of most nearby galaxies. Infrared color-magnitude diagrams are given illustrating the distribution of different asymptotic giant branch stars and the locations of young stellar objects. Finally, the average SED of H II/star formation regions is compared to the equivalent Large Magellanic Cloud average H II/star formation region SED. These preliminary results will be expanded in detail in subsequent papers
The complex environment of the bright carbon star TX Psc as probed by spectro-astrometry
Context: Stars on the asymptotic giant branch (AGB) show broad evidence of
inhomogeneous atmospheres and circumstellar envelopes. These have been studied
by a variety of methods on various angular scales. In this paper we explore the
envelope of the well-studied carbon star TX Psc by the technique of
spectro-astrometry. Aims: We explore the potential of this method for detecting
asymmetries around AGB stars. Methods:We obtained CRIRES observations of
several CO v=1 lines near 4.6 m and HCN lines near 3 m in
2010 and 2013. These were then searched for spectro-astrometric signatures. For
the interpretation of the results, we used simple simulated observations.
Results: Several lines show significant photocentre shifts with a clear
dependence on position angle. In all cases, tilde-shaped signatures are found
where the positive and negative shifts (at PA 0deg) are associated with blue
and weaker red components of the lines. The shifts can be modelled with a
bright blob 70 mas to 210 mas south of the star with a flux of several percent
of the photospheric flux. We estimate a lower limit of the blob temperature of
1000 K. The blob may be related to a mass ejection as found for AGB stars or
red supergiants. We also consider the scenario of a companion object.
Conclusions: Although there is clear spectro-astrometric evidence of a rather
prominent structure near TX Psc, it does not seem to relate to the other
evidence of asymmetries, so no definite explanation can be given. Our data thus
underline the very complex structure of the environment of this star, but
further observations that sample the angular scales out to a few hundred
milli-arcseconds are needed to get a clearer picture
The MIPSGAL View of Supernova Remnants in the Galactic Plane
We report the detection of Galactic supernova remnants (SNRs) in the mid-infrared (at 24 and 70 μm), in the coordinate ranges 10° < l < 65° and 285° < l < 350°, |b| < 1°, using MIPS aboard the Spitzer Space Telescope. We search for infrared counterparts to SNRs in Green's catalog and identify 39 out of 121, i.e., a detection rate of about 32%. Such a relatively low detection fraction is mainly due to confusion with nearby foreground/background sources and diffuse emission. The SNRs in our sample show a linear trend in [F_8/F_(24)] versus [F_(70)/F_(24)]. We compare their infrared fluxes with their corresponding radio flux at 1.4 GHz and find that most remnants have a ratio of 70 μm to 1.4 GHz which is similar to those found in previous studies of SNRs (with the exception of a few that have ratios closer to those of H II regions). Furthermore, we retrieve a slope close to unity when correlating infrared (24 and 70 μm) with 1.4 GHz emission. Our survey is more successful in detecting remnants with bright X-ray emission, which we find is well correlated with the 24 μm morphology. Moreover, by comparing the power emitted in the X-ray, infrared, and radio, we conclude that the energy released in the infrared is comparable to the cooling in the X-ray range
Catching the fish - Constraining stellar parameters for TX Psc using spectro-interferometric observations
Stellar parameter determination is a challenging task when dealing with
galactic giant stars. The combination of different investigation techniques has
proven to be a promising approach. We analyse archive spectra obtained with the
Short-Wavelength-Spectrometer (SWS) onboard of ISO, and new interferometric
observations from the Very Large Telescope MID-infrared Interferometric
instrument (VLTI/MIDI) of a very well studied carbon-rich giant: TX Psc. The
aim of this work is to determine stellar parameters using spectroscopy and
interferometry. The observations are used to constrain the model atmosphere,
and eventually the stellar evolutionary model in the region where the tracks
map the beginning of the carbon star sequence. Two different approaches are
used to determine stellar parameters: (i) the 'classic' interferometric
approach where the effective temperature is fixed by using the angular diameter
in the N-band (from interferometry) and the apparent bolometric magnitude; (ii)
parameters are obtained by fitting a grid of state-of-the-art hydrostatic
models to spectroscopic and interferometric observations. We find a good
agreement between the parameters of the two methods. The effective temperature
and luminosity clearly place TX Psc in the carbon-rich AGB star domain in the
H-R-diagram. Current evolutionary tracks suggest that TX Psc became a C-star
just recently, which means that the star is still in a 'quiet' phase compared
to the subsequent strong-wind regime. This is in agreement with the C/O ratio
being only slightly larger than 1.Comment: 11 pages, 9 figures, 5 table
Analysis of the thin layer of Galactic warm ionized gas in the range 20 < l < 30 deg, -1.5 < b < +1.5 deg
We present an analysis of the thin layer of Galactic warm ionized gas at an
angular resolution ~ 10'. This is carried out using radio continuum data at 1.4
GHz, 2.7 GHz and 5 GHz in the coordinate region 20 < l < 30 deg, -1.5 < b <
+1.5 deg. For this purpose, we evaluate the zero level of the 2.7 and 5 GHz
surveys using auxiliary data at 2.3 GHz and 408 MHz. The derived zero level
corrections are T_{zero}(2.7 GHz)=0.15 +/- 0.06 K and T_{zero}(5 GHz)=0.1 +/-
0.05 K. We separate the thermal (free-free) and non-thermal (synchrotron)
component by means of a spectral analysis performed adopting an antenna
temperature spectral index -2.1 for the free-free emission, a realistic spatial
distribution of indices for the synchrotron radiation and by fitting,
pixel-by-pixel, the Galactic spectral index. We find that at 5 GHz, for |b| = 0
deg, the fraction of thermal emission reaches a maximum value of 82%, while at
1.4 GHz, the corresponding value is 68%. In addition, for the thermal emission,
the analysis indicates a dominant contribution of the diffuse component
relative to the source component associated with discrete HII regions.Comment: 9 pages, 9 figures, accepted to MNRA
OC030: Three‐dimensional ultrasound enhances the identification of vermian fissures in the normal and abnormal cerebellum
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