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Register a new userRadio and Infrared observations of Transition Objects
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L. Cerrigone
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Observing objects in transition from pre- to young Planetary Nebula (PN), when the central star radiation starts to excite the envelope, can help us to understand the evolution of the circumstellar ejecta and their shaping mechanism/s. In our project we have selected a sample of hot post-AGB stars as Transition Phase candidates. Radio observations have led to detect free-free radiation from an ionized shell in about half of our targets, providing us with two sub-samples of ionized and non ionized Transition Objects. We are now using IRAC and IRS on the Spitzer Space Telescope to determine if extended emission is present (IRAC) and to study our targets chemistry (IRS). In particular, by comparing spectra from the two sub-samples, the IRS observations will enable us to check how the presence of an ionization front effects the circumstellar envelope. The IRAC measurements, combined with previous ones in the literature, will give us information on the extent and physical conditions of the dust components.
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We present infrared observations of four young stellar objects using the Palomar Testbed Interferometer (PTI). For three of the sources, T Tau, MWC 147 and SU Aur, the 2.2 micron emission is resolved at PTIs nominal fringe spacing of 4 milliarcsec (mas), while the emission region of AB Aur is over-resolved on this scale. We fit the observations with simple circumstellar material distributions and compare our data to the predictions of accretion disk models inferred from spectral energy distributions. We find that the infrared emission region is tenths of AU in size for T Tau and SU Aur and ~1 AU for MWC 147.
We report on the first near-infrared observations obtained for Rotating RAdio Transients (RRATs). Using adaptive optics devices mounted on the ESO Very Large Telescope (VLT), we observed two objects of this class: RRAT J1819-1458, and RRAT J1317-5759. These observations have been performed in 2006 and 2008, in the J, H and Ks bands. We found no candidate infrared counterpart to RRAT J1317-5759, down to a limiting magnitude of Ks ~ 21. On the other hand, we found a possible candidate counterpart for RRAT J1819-1458, having a magnitude of Ks=20.96+/-0.10 . In particular, this is the only source within a 1 sigma error circle around the sources accurate X-ray position, although given the crowded field we cannot exclude that this is due to a chance coincidence. The infrared flux of the putative counterpart to the highly magnetic RRAT J1819-1458, is higher than expected from a normal radio pulsar, but consistent with that seen from magnetars. We also searched for the near-infrared counterpart to the X-ray diffuse emission recently discovered around RRAT J1819-1458, but we did not detect this component in the near-infrared band. We discuss the luminosity of the putative counterpart to RRAT J1819-1458, in comparison with the near-infrared emission of all isolated neutron stars detected to date in this band (5 pulsars and 7 magnetars).
We present observations of the Cygnus OB2 region obtained with the Giant Metrewave Radio Telescope (GMRT) at the frequencies of 325 MHz and 610 MHz. In this contribution we focus on the study of proplyd-like objects (also known as free-floating Evaporating Gas Globules or frEGGs) that typically show an extended cometary morphology. We identify eight objects previously studied at other wavelengths and derive their physical properties by obtaining their optical depth at radio-wavelengths. Using their geometry and the photoionization rate needed to produce their radio-continuum emission, we find that these sources are possibly ionized by a contribution of the stars Cyg OB2 #9 and Cyg OB2 #22. Spectral index maps of the eight frEGGs were constructed, showing a flat spectrum in radio frequencies in general. We interpret these as produced by optically-thin ionized gas, although it is possible that a combination of thermal emission, not necessarily optically thin, produced by a diffuse gas component and the instrument response (which detects more diffuse emission at low frequencies) can artificially generate negative spectral indices. In particular, for the case of the Tadpole we suggest that the observed emission is not of non-thermal origin despite the presence of regions with negative spectral indices in our maps.
We have measured mid-infrared radiation from an orientation-unbiased sample of 3CRR galaxies and quasars at redshifts 0.4 < z < 1.2 with the IRS and MIPS instruments on the Spitzer Space Telescope. Powerful emission (L_24micron > 10^22.4 W/Hz/sr) was detected from all but one of the sources. We fit the Spitzer data as well as other measurements from the literature with synchrotron and dust components. The IRS data provide powerful constraints on the fits. At 15 microns, quasars are typically four times brighter than radio galaxies with the same isotropic radio power. Based on our fits, half of this difference can be attributed to the presence of non-thermal emission in the quasars but not the radio galaxies. The other half is consistent with dust absorption in the radio galaxies but not the quasars. Fitted optical depths are anti-correlated with core dominance, from which we infer an equatorial distribution of dust around the central engine. The median optical depth at 9.7 microns for objects with core-dominance factor R > 10^-2 is approximately 0.4; for objects with R < 10^-2, it is 1.1. We have thus addressed a long-standing question in the unification of FR II quasars and galaxies: quasars are more luminous in the mid-infrared than galaxies because of a combination of Doppler-boosted synchrotron emission in quasars and extinction in galaxies, both orientation-dependent effects.
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