1,404 research outputs found
A search for symbiotic behaviour amongst OH/IR colour mimics
Recent maser surveys have shown that many potential OH/IR stars have no OH
masers in their circumstellar envelopes, despite the modest requirements which
should be implicitly met by IRAS colour-selected candidates. It has been
suggested that these OH/IR colour mimics must have a degenerate companion which
dissociates OH molecules and disrupts the masing action, ie. that they are
related to symbiotic Miras. Coincidentally, there is a paucity of long-period
symbiotic Miras and symbiotic OH/IR stars. Phenomonologically, those that are
known seem to cluster in the zone where field Miras transform into OH/IR stars.
If it could be proven that OH/IR colour mimics contain a degenerate star, that
observable evidence of this star is hidden from view by CS dust whilst it
slowly accretes from the wind of its Mira companion, then we have an excellent
explanation for not only the existence of OH/IR colour mimics, but also for the
low observed frequency of symbiotic OH/IR stars and the common occurrence of
very slow novae in long-period symbiotic Miras. Here, we employ radio continuum
radiation (which should escape unhindered from within the dust shells) as a
simple probe of the postulated hot degenerate companions which would inevitably
ionize a region of their surrounding gas. We compare the radio and infrared
properties of the colour mimics with those of normal symbiotic Miras, using the
strong correlation between radio and mid-IR emission in symbiotic stars. We
show that if a hot companion exists then, unlike their symbiotic counterparts,
they must produce radiation-bounded nebulae. Our observations provide no
support for the above scenario for the lack of observed masers, but neither do
they permit a rejection of this scenario.Comment: 6 pages; no figures attached; LaTeX (MN style); postscript figures
via anonymous ftp in users/ers/mimic-figs on astro.caltech.edu; University of
Toronto pre-print; ERSRJI
Herschel and SCUBA-2 imaging and spectroscopy of a bright, lensed submillimetre galaxy at z = 2.3
We present a detailed analysis of the far-infrared (-IR) properties of the bright, lensed, z = 2.3, submillimetre-selected galaxy (SMG), SMMâJ2135-0102 (hereafter SMMâJ2135), using new observations with Herschel, SCUBA-2 and the Very Large Array (VLA). These data allow us to constrain the galaxy's spectral energy distribution (SED) and show that it has an intrinsic rest-frame 8-1000-ÎŒm luminosity, L_(bol), of (2.3±0.2) Ă 10^(12) L_â and a likely star-formation rate (SFR) of ~400 yr-1. The galaxy sits on the far-IR/radio correlation for far-IR-selected galaxies. At âł70 ÎŒm, the SED can be described adequately by dust components with dust temperatures, T_d ~ 30 and 60 k. Using SPIRE's Fourier- transform spectrometer (FTS) we report a detection of the [C ii]â158 ÎŒm cooling line. If the [C ii], CO and far-IR continuum arise in photo-dissociation regions (PDRs), we derive a characteristic gas density, n ~ 10^3 cm^(-3), and a far-ultraviolet (-UV) radiation field, G_0, 10^(3)Ă stronger than the Milky Way. L_[CII]/L_(bol) is significantly higher than in local ultra-luminous IR galaxies (ULIRGs) but similar to the values found in local star-forming galaxies and starburst nuclei. This is consistent with SMMâJ2135 being powered by starburst clumps distributed across ~2 kpc, evidence that SMGs are not simply scaled-up ULIRGs. Our results show that SPIRE's FTS has the ability to measure the redshifts of distant, obscured galaxies via the blind detection of atomic cooling lines, but it will not be competitive with ground-based CO-line searches. It will, however, allow detailed study of the integrated properties of high-redshift galaxies, as well as the chemistry of their interstellar medium (ISM), once more suitably bright candidates have been found
Discovery of hydroxyl and water masers in R Aquarii and H1-36 Arae
We present the first results from an all-sky maser-line survey of symbiotic
Miras. Interferometric spectral-line observations of R Aqr and H1-36 Arae have
revealed a 22-GHz water maser in the former and 1612-MHz hydroxyl and weak
22-GHz water maser emission from the latter. H1-36 has thus become the first
known symbiotic OH/IR star. We have also detected weak OH line emission from
the vicinity of R Aqr, but we note that there are small discrepencies between
the OH- and H2O-line velocities and positions. These detections demonstrate
unequivocally that dust can shield some circumstellar hydroxyl and water
molecules from dissociation, even in systems which possess intense local
sources of UV. Finally, we discuss some of the implications of these
observations. The narrow profile of the water maser in R Aqr means that there
may finally be an opportunity to determine the system's orbital parameters. We
also point out that high resolution synthesis observations may trace the
distribution of dust in H1-36 and R Aqr, possibly throwing light on the
mass-loss process in symbiotic Miras and placing constraints on the amount of
collimation experienced by UV radiation from their hot, compact companions.Comment: 7 pages; no figures attached; LaTex (MN style); postscript figures
via anonymous ftp in /users/ers on astro.caltech.edu; University of Toronto
pre-print; ERSRJI
Mm/submm observations of symbiotic binary stars: implications for the mass loss and mass exchange
We discuss mm/submm spectra of a sample of symbiotic binary systems, and
compare them with popular models proposed to account for their radio emission.
We find that radio emission from quiescent S-type systems originates from a
conical region of the red giant wind ionized by the hot companion (the STB
model), whereas more complicated models involving winds from both components
and their interaction are required to account for radio emission of active
systems. We also find that the giant mass-loss rates derived from our
observations are systematically higher than those for single cool giants. This
result is in agreement with conclusions derived from IRAS observations and with
requirements of models for the hot component.Comment: 7 pages, 8 figures. Paper presented at COSPAR 2000 "New results in
FIR and Submm Astronomy", to be published in Advances in Space Researc
The evolutionary sequence of active galactic nuclei and galaxy formation revealed
Today, almost every galaxy spheroid contains a massive black hole: a remnant of, and testament to, a period in its evolution when it contained an active galactic nucleus (AGN). However, the sequence and timescales of the formation of the black hole and surrounding spheroid of stars are completely unknown, leaving a large gap in our knowledge of how the universe attained its present appearance. Here we present submillimeter observations of matched samples of X-ray absorbed and unabsorbed AGNs that have luminosities and redshifts characteristic of the sources responsible for most of the mass in present-day black holes. Strong submillimeter emission, an isotropic signature of copious star formation, is found only in the X-rayâabsorbed sample, ruling out orientation effects as the cause of the absorption. The space density and luminosity range of the X-rayâabsorbed AGNs indicate that they are undergoing the transition between a hidden growth phase and an unabsorbed AGN phase and imply that the X-rayâabsorbed period in the AGN's evolution coincides with the formation of the galaxy spheroid
X-ray absorbed QSOs and the QSO evolutionary sequence
Unexpected in the AGN unified scheme, there exists a population of broad-line
z~2 QSOs which have heavily absorbed X-ray spectra. These objects constitute
10% of the population at luminosities and redshifts characteristic of the main
producers of QSO luminosity in the Universe. Our follow up observations in the
submm show that these QSOs are often embedded in ultraluminous starburst
galaxies, unlike most QSOs at the same redshifts and luminosities. The
radically different star formation properties between the absorbed and
unabsorbed QSOs implies that the X-ray absorption is unrelated to the torus
invoked in AGN unification schemes. Instead, these results suggest that the
objects represent a transitional phase in an evolutionary sequence relating the
growth of massive black holes to the formation of galaxies. The most puzzling
question about these objects has always been the nature of the X-ray absorber.
We present our study of the X-ray absorbers based on deep (50-100ks) XMM-Newton
spectroscopy. We show that the absorption is most likely due to a dense ionised
wind driven by the QSO. This wind could be the mechanism by which the QSO
terminates the star formation in the host galaxy, and ends the supply of
accretion material, to produce the present day black hole/spheroid mass ratio.Comment: 4 pages, to appear in conference proceedings "Studying Galaxy
Evolution with Spitzer and Herschel
- âŠ