The T Tauri star RY Tau has increased its brightness from V=10.6mag to V=9.6mag in October-November 1996. By February-March 1997, the star has faded again to V=10.8mag. High-resolution echelle spectra of RY Tau were obtained wit h the SOFIN spectrograph at the Nordic Optical Telescope (La Palma, Spain) at lo w and high brightness levels of the star. No significant changes in the photosph eric lines, which are sensitive to temperature and gravity, were noticed. The spectral type of RY Tau is defined as G1-2IV, which in combination with photomet ric data implies A_V_=1.0-1.3mag. Polarimetric patrol of RY Tau during the fadin g of the star showed an increase of its intrinsic polarization from 0.5-1.0% at high brightness to about 2% at low brightness in the V, R and I bands. The flux radiated in H{alpha} and the IR Ca II emission lines remained about the same, in spite of the one magnitude difference in the continuum flux. These results indicate that variable obscuration of the star by circumstellar dust clo uds was responsible for the brightness change of RY Tau, and that the emission l ine source is mostly outside of the obscured region.
Transitional disks represent a short stage of the evolution of circumstellar material. Studies of dust grains in these objects can provide pivotal information on the mechanisms of planet formation. Dissimilarities in the spatial distribution of small ({mu}m-size) and large (mm-size) dust grains have recently been pointed out. Constraints on the small dust grains can be obtained by imaging the distribution of scattered light at near-infrared wavelengths. We aim at resolving structures in the surface layer of transitional disks (with particular emphasis on the inner 10-50AU), thus increasing the scarce sample of high-resolution images of these objects. We obtained VLT/NACO near-IR high-resolution polarimetric differential imaging observations of SAO 206462 (HD135344B). This technique allows one to image the polarized scattered light from the disk without any occulting mask and to reach an inner working angle of ~0.1". A face-on disk is detected in H and K_s_ bands between 0.1" and 0.9". No significant differences are seen between the H and K_s_ images. In addition to the spiral arms, these new data allow us to resolve for the first time an inner disk cavity for small dust grains. The cavity size (=~28AU) is much smaller than what is inferred for large dust grains from (sub-)mm observations (39 to 50AU). This discrepancy cannot be ascribed to any resolution effect. The interaction between the disk and potential orbiting companion(s) can explain both the spiral arm structure and the discrepant cavity sizes for small and large dust grains. One planet may be carving out the gas (and, thus, the small grains) at 28AU, and generating a pressure bump at larger radii (39AU), which holds back the large grains. We analytically estimate that, in this scenario, a single giant planet (with a mass between 5 and 15M_J_) at 17 to 20AU from the star is consistent with the observed cavity sizes.
SCUPOL, the polarimeter for SCUBA on the James Clerk Maxwell Telescope, was the most prolific thermal imaging polarimeter built to date. Between 1997 and 2005, observations of 104 regions were made at 850um in the mapping mode. The instrument has produced ~50 refereed journal publications, and that number is still growing. We have systematically re-reduced all imaging polarimetry made in the standard "jiggle-map" mode from the SCUBA archive (2800+ individual observations) to produce a catalog of SCUPOL images and tables. We present the results of our analysis with figures and data tables produced for all 83 regions where significant polarization was detected. In addition, the reduced data cubes and data tables can be accessed online. In many cases, the data included in this paper have been previously published elsewhere. However, this publication includes unpublished data sets, in whole or in part, toward 39 regions, including cores in Rho Ophiuchus, Orion's OMC-2 region, several young stellar objects, and the galaxy M87.
Gravitational microlensing is a powerful tool for probing the inner structure of distant quasars. In this context, we have obtained spectropolarimetric observations of the two images of the broad absorption line (BAL) quasar SDSS J081830.46+060138.0 (J0818+0601) at redshift z~~2.35. We first show that J0818+0601 is actually gravitationally lensed, and not a binary quasar. A strong absorption system detected at z=1.0065+/-0.0002 is possibly due to the lensing galaxy. Microlensing is observed in one image and it magnifies the emission lines, the continuum, and the BALs differently. By disentangling the part of the spectrum that is microlensed from the part that is not microlensed, we unveil two sources of continuum that must be spatially separated: a compact one, which is microlensed, and an extended one, which is not microlensed and contributes to two thirds of the total continuum emission. J0818+0601 is the second BAL quasar in which an extended source of rest-frame ultraviolet continuum is found. We also find that the images are differently polarized, suggesting that the two continua might be differently polarized. Our analysis provides constraints on the BAL flow. In particular, we find that the outflow is seen with a nonzero onset velocity, and stratified according to ionization.
Deep optical surveys open the avenue for finding large numbers of BL Lac objects that are hard to identify because they lack the unique properties classifying them as such. While radio or X-ray surveys typically reveal dozens of sources, recent compilations based on optical criteria alone have increased the number of BL Lac candidates considerably. However, these compilations are subject to biases and may contain a substantial number of contaminating sources. In this paper we extend our analysis of 182 optically selected BL Lac object candidates from the SDSS with respect to an earlier study. The main goal is to determine the number of bona fide BL Lac objects in this sample. We examine their variability characteristics, determine their broad-band radio-UV spectral energy distributions (SEDs), and search for the presence of a host galaxy. In addition we present new optical spectra for 27 targets with improved signal-to-noise ratio with respect to the SDSS spectra. At least 59% of our targets have shown variability between SDSS DR2 and our observations by more than 0.1-0.27mag depending on the telescope used. A host galaxy was detected in 36% of our targets. The host galaxy type and luminosities are consistent with earlier studies of BL Lac host galaxies. Simple fits to broad-band SEDs for 104 targets of our sample derived synchrotron peak frequencies between 13.5<=log_10_({nu}_peak_)<=16 with a peak at log_10_~14.5. Our new optical spectra do not reveal any new redshift for any of our objects. Thus the sample contains a large number of bona fide BL Lac objects and seems to contain a substantial fraction of intermediate-frequency peaked BL Lacs.
We have carried out the Sino-German 6cm polarisation survey of the Galactic plane at 6cm in total and polarised intensity using the Urumqi 25-m telescope of Xinjiang (formerly Urumqi) Astronomical Observatory, Chinese Academy of Sciences. The angular resolution is 9.5-arcmin. The surveyed area covers 10{deg} to 230{deg} in Galactic longitude and absolute Galactic latitudes of up to 5{deg}. The measured rms-noise is about 6.1 mJy/beam area for total intensities and 3.05mJy/beam area for polarised intensities. The survey maps are accessible from http://zmtt.bao.ac.cn/6cm/ .
We present the results of optical (R-band) photometric and polarimetric monitoring and Very Long Baseline Array imaging of the blazar S4 0954+658, along with Fermi {gamma}-ray data during a multi-waveband outburst in 2011 March-April. After a faint state with a brightness level R~17.6mag registered in the first half of 2011 January, the optical brightness of the source started to rise and reached ~14.8mag during the middle of March, showing flare-like behavior. The most spectacular case of intranight variability was observed during the night of 2011 March 9, when the blazar brightened by ~0.7mag within 7hr. During the rise of the flux, the position angle of the optical polarization rotated smoothly over more than 300{deg}. At the same time, within 1{sigma} uncertainty, a new superluminal knot appeared with an apparent speed of 19.0+/-0.3c. We have very strong evidence that this knot is associated with the multi-waveband outburst in 2011 March-April. We also analyze the multi-frequency behavior of S4 0954+658 during a number of minor outbursts from 2008 August to 2012 April. We find some evidence of connections between at least two additional superluminal ejecta and near-simultaneous optical flares.
Polarimetric studies of light transmitted through interstellar clouds may give constraints on the properties of the interstellar dust grains. Traditionally, broadband linear polarisation (BBLP) measurements have been considered an important diagnostic tool for the study of the interstellar dust, while comparatively less attention has been paid to spectropolarimetric measurements. However, spectropolarimetry may offer stronger constraints than BBLP, for example by revealing narrowband features, and by allowing us to distinguish the contribution of dust from the contribution of interstellar gas. Therefore, we have decided to carry out a Large Interstellar Polarisation Survey (LIPS) using spectropolarimetric facilities in both hemispheres. Here we present the results obtained in the Southern Hemisphere with the FORS2 instrument of the ESO Very Large Telescope.
We present and discuss optical polarimetry of a large group (60 objects) of peculiar early-type stars (Herbig Ae/Be stars and candidate members, B[e] stars, extreme emission line objects etc.). Most were taken from ``A new catalogue of members and candidate members of Herbig Ae/Be stellar group'' The et al. (1994, Cat. <J/A+AS/104/315>). For 40 out of the 60 objects polarization was measured for the first time. On the basis of the data we draw conclusions about the circumstellar shell configuration and orientation for several objects. Polarimetric variability on different time-scales (minutes...hours...days) was investigated, as well as comparison with earlier measurements to investigate variability over longer time-scales. No circular polarization was detected to a 5{sigma} level in most of the investigated stars. Polarimetric data obtained here as well as data available from the literature were analyzed from the point of investigating the evolutionary status of the objects. The relationship between the polarimetric and photometric data was also investigated.
The S-band Polarisation All-Sky Survey (S-PASS) has observed the entire southern sky using the 64-metre Parkes radio telescope at 2.3GHz with an effective bandwidth of 184MHz. The surveyed sky area covers all declinations DE<0{deg}. To analyse compact sources the survey data have been re-processed to produce a set of 107 Stokes I maps with 10.75-arcmin resolution and the large scale emission contribution filtered out. In this paper we use these Stokes I images to create a total intensity southern-sky extragalactic source catalogue at 2.3GHz. The source catalogue contains 23389 sources and covers a sky area of 16600deg^2^, excluding the Galactic plane for latitudes |b|<10{deg}. Approximately 8% of catalogued sources are resolved. S-PASS source positions are typically accurate to within 35-arcsec. At a flux density of 225mJy the S-PASS source catalogue is more than 95% complete, and ~94% of S-PASS sources brighter than 500mJy/beam have a counterpart at lower frequencies.
