195 research outputs found
Cleaning up Eta Carinae: Detection of Ammonia in the Homunculus
We report the first detection of ammonia in the Homunculus nebula around eta
Carinae, which is also the first detection of emission from a polyatomic
molecule in this or any other luminous blue variable (LBV) nebula. Observations
of the NH3 (J,K)=(3,3) inversion transition made with the Australia Telescope
Compact Array reveal emission at locations where infrared H2 emission had been
detected previously, near the strongest dust emission in the core of the
Homunculus. We also detect ammonia emission from the so-called ``strontium
filament'' in the equatorial disk. The presence of NH3 around eta Car hints
that molecular shells around some Wolf-Rayet stars could have originated in
prior LBV eruptions, rather than in cool red supergiant winds or the ambient
interstellar medium. Combined with the lack of any CO detection, NH3 seems to
suggest that the Homunculus is nitrogen rich like the ionized ejecta around eta
Car. It also indicates that the Homunculus is a unique laboratory in which to
study unusual molecule and dust chemistry, as well as their rapid formation in
a nitrogen-rich environment around a hot star. We encourage future observations
of other transitions like NH3 (1,1) and (2,2), related molecules like N2H+, and
renewed attempts to detect CO.Comment: 4 pages, accepted to ApJ letter
High Mass Starless Cores
We report the identification of a sample of potential High-Mass Starless
Cores (HMSCs). The cores were discovered by comparing images of the fields
containing candidate High-Mass Protostellar Objects (HMPOs) at 1.2mm and
mid-infrared (8.3um; MIR) wavelengths. While the HMPOs are detected at both
wavelengths, several cores emitting at 1.2mm in the same fields show absorption
or no emission at the MIR wavelength. We argue that the absorption is caused by
cold dust. The estimated masses of a few 10^2Msun - 10^3 Msun and the lack of
IR emission suggests that they may be massive cold cores in a pre-stellar
phase, which could presumably form massive stars eventually. Ammonia (1,1) and
(2,2) observations of the cores indicate smaller velocity dispersions and lower
rotation temperatures compared to HMPOs and UCHII regions suggesting a
quiescent pre-stellar stage. We propose that these newly discovered cores are
good candidates for the HMSC stage in high-mass star-formation. This sample of
cores will allow us to study the high-mass star and cluster formation processes
at the earliest evolutionary stages.Comment: 7 pages, 3 figures, 1 table, to be published in ApJL, author names
replaced with comma separatio
F-GAMMA: Variability Doppler factors of blazars from multiwavelength monitoring
Recent population studies have shown that the variability Doppler factors can
adequately describe blazars as a population. We use the flux density variations
found within the extensive radio multi-wavelength datasets of the F-GAMMA
program, a total of 10 frequencies from 2.64 up to 142.33 GHz, in order to
estimate the variability Doppler factors for 58 -ray bright sources,
for 20 of which no variability Doppler factor has been estimated before. We
employ specifically designed algorithms in order to obtain a model for each
flare at each frequency. We then identify each event and track its evolution
through all the available frequencies for each source. This approach allows us
to distinguish significant events producing flares from stochastic variability
in blazar jets. It also allows us to effectively constrain the variability
brightness temperature and hence the variability Doppler factor as well as
provide error estimates. Our method can produce the most accurate (16\% error
on average) estimates in the literature to date.Comment: 9 pages, 7 figures, accepted for publication in MNRA
Radio jet emission from GeV-emitting narrow-line Seyfert 1 galaxies
We studied the radio emission from four radio-loud and gamma-ray-loud
narrow-line Seyfert 1 galaxies. The goal was to investigate whether a
relativistic jet is operating at the source, and quantify its characteristics.
We relied on the most systematic monitoring of such system in the cm and mm
radio bands which is conducted with the Effelsberg 100 m and IRAM 30 m
telescopes and covers the longest time-baselines and the most radio frequencies
to date. We extract variability parameters and compute variability brightness
temperatures and Doppler factors. The jet powers were computed from the light
curves to estimate the energy output. The dynamics of radio spectral energy
distributions were examined to understand the mechanism causing the
variability. All the sources display intensive variability that occurs at a
pace faster than what is commonly seen in blazars. The flaring events show
intensive spectral evolution indicative of shock evolution. The brightness
temperatures and Doppler factors are moderate, implying a mildly relativistic
jet. The computed jet powers show very energetic flows. The radio polarisation
in one case clearly implies a quiescent jet underlying the recursive flaring
activity. Despite the generally lower flux densities, the sources appear to
show all typical characteristics seen in blazars that are powered by
relativistic jets.Comment: Accepted for publication in 4 - Extragalactic astronomy of Astronomy
and Astrophysic
Turbulent Flow-Driven Molecular Cloud Formation: A Solution to the Post-T Tauri Problem?
We suggest that molecular clouds can be formed on short time scales by
compressions from large scale streams in the interstellar medium (ISM). In
particular, we argue that the Taurus-Auriga complex, with filaments of 10-20 pc
2-5 pc, most have been formed by H I flows in Myr,
explaining the absence of post-T Tauri stars in the region with ages Myr. Observations in the 21 cm line of the H I `halos' around the Taurus
molecular gas show many features (broad asymmetric profiles, velocity shifts of
H I relative to CO) predicted by our MHD numerical simulations, in which
large-scale H I streams collide to produce dense filamentary structures. This
rapid evolution is possible because the H I flows producing and disrupting the
cloud have much higher velocities (5-10 kms) than present in the molecular gas
resulting from the colliding flows. The simulations suggest that such flows can
occur from the global ISM turbulence without requiring a single triggering
event such as a SN explosion.Comment: 26 pages, 12 ps figures. Apj accepte
86 GHz polarimetry of OVV1633+382 after a major mm flare
The 18 mag QSO 1633+382 (4C38.41, z=1.807) showed a very pronounced outburst
in 2001/2002. With a peak amplitude of more than 9 Jy at 90GHz, this flare was
brighter than any known previous flare in this source (data available since
1980).During onset, the mm-flare was particulary fast, with an increase of more
than 2 Jy at 230 GHz in less than 8 days. Since January 2002, the mm-flux of
1633+382 is decaying. During this decline, however, local flux variations with
amplitudes of 1-3 Jy were seen, indicative of underlying and more rapid source
activity on time scales of 1-2 months. After the main peak occurring in
2001.99, the 90 GHz flux showed secondary maxima at approximately half year
intervals in 2002.3, 2002.7 and 2003.13. This kind of periodicity might be
explained via the lighthouse model (Camenzind and Krockenberger 1992), which is
based on the magnetic accelerator of Blanford and Payne (1982). At present the
millimeter flux is nearly back to its quiescent level of 2-2.5 Jy, which the
source had before the flare began. Our VLBA Polarimetry monitoring started June
2002 during the onset of the flare. At cm wavelength, the flare is only
marginally detected which implies very high opacity of the source.Comment: 4 pages. 5 figures. Proceedings of the 7th European VLBI Network
Symposium held in Toledo, Spain on October 12-15, 2004. Editors: R.
Bachiller, F. Colomer, J.-F. Desmurs, P. de Vicente (Observatorio Astronomico
Nacional), p. 85-88. Needs evn2004.cl
Molecular Line Observations of a Carbon-Chain-Rich Core L492
We report on molecular abundances and distributions in a starless dense core
L492. We have found that the abundances of carbon-chain molecules such as CCS,
CS, HCN, HCN, and HCN are comparable to those in
chemically young dark cloud cores called "carbon-chain--producing regions",
such as L1495B, L1521B, L1521E, and TMC-1. This is the first dark cloud core
with extremely rich in carbon-chain-molecules that is found outside the Taurus
region. In addition, the deuterium fractionation ratios of DNC/HNC and
DCO/HCO are also comparable to those in carbon-chain--producing
regions, being significantly lower than those in the evolved prestellar cores
such as L1498 and L1544. On the other hand, the abundances of NH and
NH are systematically higher than those in carbon-chain--producing
regions. Our mapping observations reveal that the central hole of molecular
distributions, which were reported for CCS and CS in evolved prestellar
cores is not significant in L492, indicating that the depletion factor of
molecules is not very high. Furthermore, L492 is dynamically more evolved than
carbon-chain--producing regions, and the protostellar collapse has started like
L1498 and L1544. Therefore, it is likely that the chemical and dynamical
evolutionary stage of L492 is intermediate between carbon-chain--producing
regions (L1495B, L1521B, L1521E, and TMC-1) and evolved prestellar cores (L1498
and L1544).Comment: 26 pages, 8 figures, accepted for publication in The Astrophysical
Journal (Preprint with high resolution figures will be available at
http://www.nro.nao.ac.jp/library/report/list.html
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