We review progress over the past decade in observations of large-scale star formation, with a focus on the interface between extragalactic and Galactic studies. Methods of measuring gas contents and star-formation rates are discussed, and updated prescriptions for calculating star-formation rates are provided. We review relations between star formation and gas on scales ranging from entire galaxies to individual molecular clouds.

Star Formation in the Milky Way and Nearby Galaxies

Of the over 150 different molecular species detected in the interstellar and circumstellar media, approximately 50 contain 6 or more atoms. These molecules, labeled complex by astronomers if not by chemists, all contain the element carbon and so can be called organic. In the interstellar medium, complex molecules are detected in the denser sources only. Although, with one exception, complex molecules have only been detected in the gas phase, there is strong evidence that they can be formed in ice mantles on interstellar grains. The nature of the gaseous complex species depends dramatically on the source where they are found: in cold, dense regions they tend to be unsaturated (hydrogen-poor) and exotic, whereas in young stellar objects, they tend to be quite saturated (hydrogen-rich) and terrestrial in nature. Based on both their spectra and chemistry, complex molecules are excellent probes of the physical conditions and history of the sources where they reside. Because they are detected in young stellar objects, complex molecules are expected to be common ingredients for new planetary systems. In this review, we discuss both the observation and chemistry of complex molecules in assorted interstellar regions in the Milky Way.

/pdf/complex-organic-interstellar-molecules-sz3r2nq94z.pdf

Complex Organic Interstellar Molecules

Astronomical data analysis software and systems

A stellar spectral flux library of wide spectral coverage and an example of its application are presented. The new library consists of 131 flux-calibrated spectra, encompassing all normal spectral types and luminosity classes at solar abundance, and metal-weak and metal-rich F-K dwarf and G-K giant components. Each library spectrum was formed by combining data from several sources overlapping in wavelength coverage. The SIMBAD database, measured colors, and line strengths were used to check that each input component has closely similar stellar type. The library has complete spectral coverage from 1150 to 10620 Afor all components and to 25000 Afor about half of them, mainly later types of solar abundance. Missing spectral coverage in the infrared currently consists of a smooth energy distribution formed from standard colors for the relevant types. The library is designed to permit inclusion of additional digital spectra, particularly of non-solar abundance stars in the infrared, as they become available. The library spectra are each given as Fl versus l, from 1150 to 25000 Ain steps of 5 A ˚. A program to combine the library spectra in the ratios appropriate to a selected isochrone is described and an example of a spectral component signature of a composite population of solar age and metallicity is illustrated. The library spectra and associated tables are available as text files by remote electronic access.

VizieR Online Data Catalog: A Stellar Spectral Flux Library: 1150 - 25000 A (Pickles 1998)

We present the fifth release of the UMIST Database for Astrochemistry (UDfA). The new reaction network contains 6173 gas-phase reactions, involving 467 species, 47 of which are new to this release. We have updated rate coefficients across all reaction types. We have included 1171 new anion reactions and updated and reviewed all photorates. In addition to the usual reaction network, we also now include, for download, state-specific deuterated rate coefficients, deuterium exchange reactions and a list of surface binding energies for many neutral species. Where possible, we have referenced the original source of all new and existing data. We have tested the main reaction network using a dark cloud model and a carbon-rich circumstellar envelope model. We present and briefly discuss the results of these models.

/pdf/the-umist-database-for-astrochemistry-2012-29l3ep98yt.pdf

The UMIST database for astrochemistry 2012

Radio Emission from Galactic Wolf-Rayet Stars and the Structure of Wolf-Rayet Winds

Radio continuum observations of 88 O-type and early B-type stars are examined. Results are presented for a subset of these stars which forms a distance-limited sample of all OB stars within 2.5 kpc of the sun. Mass loss rates are derived for HD 15570, HD 166734, HD 151804, HD 152408, Alpha Cam, HD 169454, and Zeta Sco. All of these very luminous OB stars are found to be losing mass at a rate on the order of 10 to the -5 solar masses/yr. Multifrequency observations confirm the free-free interpretation for Zeta Pup and provide evidence for variability in the free-free sources P Cygni and Cyg OB2 No. 12. 63 refs.

A Survey of Radio Emission from Galactic OB Stars

Mass loss from very luminous OB stars and the Cygnus superbubble

M17 is one of the youngest and most massive nearby star-formation regions in the Galaxy It features a bright H II region erupting as a blister from the side of a giant molecular cloud (GMC) Combining photometry from the Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) with complementary infrared (IR) surveys, we identify candidate young stellar objects (YSOs) throughout a 15 ? 1? field that includes the M17 complex The long sightline through the Galaxy behind M17 creates significant contamination in our YSO sample from unassociated sources with similar IR colors Removing contaminants, we produce a highly reliable catalog of 96 candidate YSOs with a high probability of association with the M17 complex We fit model spectral energy distributions to these sources and constrain their physical properties Extrapolating the mass function of 62 intermediate-mass YSOs (M > 3?M ?), we estimate that >1000 stars are in the process of forming in the extended outer regions of M17 The remaining 34 candidate YSOs are found in a 017?deg2 field containing the well-studied M17 H II region and photodissociation region (PDR), where bright diffuse mid-IR emission drastically reduces the sensitivity of the GLIMPSE point-source detections By inspecting IR survey images from IRAS and GLIMPSE, we find that M17 lies on the rim of a large shell structure ~05 in diameter (~20 pc at 21?kpc) We present maps of 12CO and 13CO (J = 2 ? 1) emission observed with the Heinrich Hertz Telescope The CO emission shows that the shell is a coherent, kinematic structure associated with M17, centered at v = 19?km s?1 The shell is an extended bubble outlining the PDR of a faint, diffuse H II region several Myr old We identify a group of candidate ionizing stars within the bubble YSOs in our catalog are concentrated around the bubble rim, providing evidence that massive star formation has been triggered by the expansion of the bubble The formation of the massive cluster ionizing the M17 H II region itself may have been similarly triggered We conclude that the star formation history in the extended environment of M17 has been punctuated by successive waves of massive star formation propagating through a GMC complex

http://iopscience.iop.org/article/10.1088/0004-637X/696/2/1278/pdf

The Extended Environment of M17: A Star Formation History

We report results from a Hubble Space Telescope (HST) and Near-Infrared Camera and Multiobject Spectrometer (NICMOS) program to study the distribution of hot neutral (molecular hydrogen) and ionized circumstellar material in the young planetary nebulae NGC 7027. HST/NICMOS provided very high spatial resolution imaging in line and continuum emission, and the stability and large dynamic range needed for investigating detailed structures in the circumstellar material. We present dramatic new images of NGC 7027 that have led to a new understanding of the structure in this important planetary nebula. The central star is clearly revealed, providing near-infrared fluxes that are used to directly determine the stellar temperature very accurately (T = 198,000 K). It is found that the photodissociation layer as revealed by near-infrared molecular hydrogen emission is very thin (ΔR ~ 6 × 1015 cm) and is biconical in shape. The interface region is structured and filamentary, suggesting the existence of hydrodynamic instabilities. We discuss evidence for the presence of one or more highly collimated, off-axis jets that might be present in NGC 7027. The NICMOS data are combined with earlier Hubble Space Telescope data to provide a complete picture of NGC 7027 using the highest spatial resolution data to date. The evolutionary future of NGC 7027 is discussed.

https://iopscience.iop.org/article/10.1086/309252/pdf

John H. Bieging

Papers

Radio Emission from Galactic Wolf-Rayet Stars and the Structure of Wolf-Rayet Winds

A Survey of Radio Emission from Galactic OB Stars

Mass loss from very luminous OB stars and the Cygnus superbubble

The Extended Environment of M17: A Star Formation History

Revealing the Photodissociation Region: HST/NICMOS Imaging of NGC 7027