Showing papers by "F. F. S. van der Tak published in 2004"
TL;DR: In this article, the transitions of a number of astrophysically interesting species are summarized, including energy levels, statistical weights, Einstein A-coefficients and collisional rate coefficients.
Abstract: Atomic and molecular data for the transitions of a number of astrophysically interesting species are summarized, including energy levels, statistical weights, Einstein A-coefficients and collisional rate coefficients. Available collisional data from quantum chemical calculations and experiments are extrapolated to higher energies. These data, which are made publically available through the WWW at this http URL, are essential input for non-LTE line radiative transfer programs. An online version of a computer program for performing statistical equilibrium calculations is also made available as part of the database. Comparisons of calculated emission lines using different sets of collisional rate coefficients are presented. This database should form an important tool in analyzing observations from current and future (sub)millimetre and infrared telescopes.
1,407 citations
TL;DR: In this article, the authors reported 5-43 GHz radio observations of the CRL 2136 region at 0.6-6 resolution, where they detected weak radio emission from the deeply embedded high-mass protostar IRS 1, which has an optically thick spectrum up to frequencies of 22 GHz, flattening at higher frequencies.
Abstract: We report 5-43 GHz radio observations of the CRL 2136 region at 0.6-6 resolution. We detect weak (mJy intensity) radio emission from the deeply embedded high-mass protostar IRS 1, which has an optically thick spectrum up to frequencies of 22 GHz, flattening at higher frequencies, which might be explained by emission from a jet. Water maser mapping shows that the strong emission observed redshifted relative to the systemic velocity is spatially coincident with the optically thick continuum emission. The H 2 O maser emission from this object (and others we know of) seems to have a different origin than most of these masers, which are frequently tracing bipolar high-velocity outflows. Instead, the CRL 2136 H 2 O emission arises in the close circumstellar environment of the protostar (within 1000 AU). We speculate that most of it is excited in the hot, dense infalling gas after the accretion shock, although this cannot explain all the H 2 O emission. An accretion shock nature for the continuum emission seems unlikely.
43 citations
TL;DR: In this paper, the spectrum of perdeuterated methanol, CD 3 OD, has been measured in the frequency range 62 −233 GHz using a one-dimensional torsion-rotation Hamiltonian.
15 citations
TL;DR: In this article, two bright mid-infrared sources are detected, as well as diffuse emission and the bright sources have associated compact radio emission and probably are young high-mass stars, and the measured sizes and estimated temperatures indicate that these sources together can supply the observed far infrared luminosity.
Abstract: Observations at mid-infrared (4.8-17.65 um) and radio (0.7-1.3 cm) wavelengths are used to constrain the structure of the high-mass star-forming region W3 IRS5 on 0.1'' (200 AU) scales. Two bright mid-infrared sources are detected, as well as diffuse emission. The bright sources have associated compact radio emission and probably are young high-mass stars.
The measured sizes and estimated temperatures indicate that these sources together can supply the observed far-infrared luminosity. However, an optically thick radio source with a possible mid-infrared counterpart may also contribute significant luminosity; if so, it must be extremely deeply embedded.
The infrared colour temperatures of 350-390 K and low radio brightness suggest gravitational confinement of the H II regions and ongoing accretion at a rate of a few 10^-8 M0/yr or more. Variations in the accretion rate would explain the observed radio variability. The low estimated foreground extinction suggests the existence of a cavity around the central stars, perhaps blown by stellar winds.
At least three radio sources without mid-infrared counterparts appear to show proper motions of ~100 km/s, and may be deeply embedded young runaway OB stars, but more likely are clumps in the ambient material which are shock-ionized by the OB star winds.
1 citations