Limits on the cosmic-ray ionization rate toward massive young stars

Recent models of the envelopes of seven massive protostars are used to analyze observations of H3+ infrared absorption and H13CO+ submillimeter emission lines toward these stars, and to constrain the cosmic-ray ionization rate zeta. The H13CO+ gives best-fit values of zeta=(2.6+/- 1.8) x 10^-17 s^-1, in good agreement with diffuse cloud models and with recent Voyager/Pioneer data but factors of up to 7 lower than found from the H3+ data. No relation of zeta with luminosity or total column density is found, so that local (X-ray) ionization and shielding against cosmic rays appear unimportant for these sources. The difference between the H3+ and H13CO+ results and the correlation of N(H3+) with heliocentric distance suggest that intervening clouds contribute significantly to the H3+ absorptions in the more distant regions. The most likely absorbers are low-density (<~10^4 cm^-3) clouds with most carbon in neutral form or in CO.Comment: To be published in A&A 358 (Letters); 4 pages including 3 figure

Observations and models of the embedded phase of high-mass star formation

This paper is a review and an update on recent work on the physical and chemical structure of the envelopes of newly born massive stars, at the stages preceding ultracompact H II regions. It discusses methods and results to determine total mass, temperature and density structure, ionization rate, and depth-dependent chemical composition.Comment: 8 pages incl 4 figures, to appear in "Hot Star Workshop III: The Earliest Phases of Massive Star Birth" (ed. P.A. Crowther) (ASP). Uses newpasp.sty (included

The chemistry of high-mass star formation

This paper reviews the chemistry of star-forming regions, with an emphasis on the formation of high-mass stars. We first outline the basic molecular processes in dense clouds, their implementation in chemical models, and techniques to measure molecular abundances. Then, recent observational, theoretical and laboratory developments are reviewed on the subjects of hot molecular cores, cosmic-ray ionization, depletion and deuteration, and oxygen chemistry. The paper concludes with a summary of outstanding problems and future opportunities.Comment: 10 A4 pages, 1 colour figure; invited review, to appear in "Massive Star Birth - A Crossroads of Astrophysics" (CUP), eds. R. Cesaroni, E. Churchwell, M. Felli, and C.M. Walmsle

Structure and Evolution of the Envelopes of Deeply Embedded Massive Young Stars

The physical structure of the envelopes around a sample of fourteen massive (1000-100,000 solar L) young stars is investigated on 100- 100,000 AU scales using maps and spectra in submillimeter continuum and lines of C17O, CS and H2CO. The total column densities and the temperature profiles are obtained by fitting self-consistent dust models to submillimeter photometry. Both the molecular line and dust emission data indicate density gradients ~r^{-alpha}, with alpha=1.0-1.5, significantly flatter than the alpha=2.0 generally found for low-mass objects. This flattening may indicate that in massive young stellar objects, nonthermal pressure is more important for the support against gravitational collapse, while thermal pressure dominates for low-mass sources. We find alpha=2 for two hot core-type sources, but regard this as an upper limit since in these objects, the CS abundance may be enhanced in the warm gas close to the star.Comment: To be published in The Astrophysical Journal. 54 pages including 14 figures Revised version with references adde

Deep Learning for Galaxy Mergers in the Galaxy Main Sequence

Starburst galaxies are often found to be the result of galaxy mergers. As a result, galaxy mergers are often believed to lie above the galaxy main sequence: the tight correlation between stellar mass and star formation rate. Here, we aim to test this claim. Deep learning techniques are applied to images from the Sloan Digital Sky Survey to provide visual-like classifications for over 340 000 objects between redshifts of 0.005 and 0.1. The aim of this classification is to split the galaxy population into merger and non-merger systems and we are currently achieving an accuracy of 91.5%. Stellar masses and star formation rates are also estimated using panchromatic data for the entire galaxy population. With these preliminary data, the mergers are placed onto the full galaxy main sequence, where we find that merging systems lie across the entire star formation rate - stellar mass plane.Comment: 4 pages, 1 figure. For Proceedings IAU Symposium No. 34

The Impact of the Massive Young Star GL 2591 on its Circumstellar Material: Temperature, Density and Velocity Structure

The temperature, density and kinematics of the gas and dust surrounding the luminous young stellar object GL~2591 are investigated on scales as small as 100 AU, probed by 4.7 micron absorption spectroscopy, to over 60,000 AU, probed by single-dish submillimeter spectroscopy. These two scales are connected by interferometric 86-226 GHz images of size 60,000 AU and resolution 2000 AU in continuum and molecular lines. The data are used to constrain the physical structure of the envelope and investigate the influence of the young star on its immediate surroundings.Comment: To be published in The Astrophysical Journal, Vol. 522 No. 2 (1999 Sep 10). 45 pages including 11 figure

A target list for searching for habitable exomoons

We investigate the habitability of hypothetical moons orbiting known exoplanets. This study focuses on big, rocky exomoons that are capable of maintaining a significant atmosphere. To determine their habitability, we calculate the incident stellar radiation and the tidal heating flux arising in the moons as the two main contributors to the energy budget. We use the runaway greenhouse and the maximum greenhouse flux limits as a definition of habitability. For each exoplanet, we run our calculations for plausible ranges of physical and orbital parameters for the moons and the planet using a Monte Carlo approach. We calculate the moon habitability probability for each planet, which is the fraction of the investigated cases that lead to habitable conditions. Based on our results, we provide a target list for observations of known exoplanets of which the top 10 planets have more than 50 per cent chance for hosting habitable moons on stable orbits. Two especially promising candidates are Kepler-62 f and Kepler-16 b, both of them with known masses and radii. Our target list can help to detect the first habitable exomoon.Peer reviewe