We present Atacama Large Millimeter/submillimeter Array (ALMA) observations from the 2014 Long Baseline Campaign in dust continuum and spectral line emission from the HL Tau region. The continuum images at wavelengths of 2.9, 1.3, and 0.87 mm have unprecedented angular resolutions of 0″. 075 (10 AU) to 0″. 025 (3.5 AU), revealing an astonishing level of detail in the circumstellar disk surrounding the young solar analog HL Tau, with a pattern of bright and dark rings observed at all wavelengths. By fitting ellipses to the most distinct rings, we measure precise values for the disk inclination (46 .72 0 .05 ± • •) and position angle (138 .02 0 .07).

A major goal of the Atacama Large Millimeter/submillimeter Array (ALMA) is to make accurate images with resolutions of tens of milliarcseconds, which at submillimeter (submm) wavelengths requires baselines up to ∼15 km. To develop and test this capability, a Long Baseline Campaign (LBC) was carried out from 2014 September to late November, culminating in end-to-end observations, calibrations, and imaging of selected Science Verification (SV) targets. This paper presents an overview of the campaign and its main results, including an investigation of the short-term coherence properties and systematic phase errors over the long baselines at the ALMA site, a summary of the SV targets and observations, and recommendations for science observing strategies at long baselines. Deep ALMA images of the quasar 3C 138 at 97 and 241 GHz are also compared to VLA 43 GHz results, demonstrating an agreement at a level of a few percent. As a result of the extensive program of LBC testing, the highly successful SV imaging at long baselines achieved angular resolutions as fine as 19 mas at ∼350 GHz. Observing with ALMA on baselines of up to 15 km is now possible, and opens up new parameter space for submm astronomy.

The age of dense interstellar cloud cores, where stars and planets form, is a crucial parameter in star formation and difficult to measure. Some models predict rapid collapse, whereas others predict timescales of more than one million years (ref. 3). One possible approach to determining the age is through chemical changes as cloud contraction occurs, in particular through indirect measurements of the ratio of the two spin isomers (ortho/para) of molecular hydrogen, H2, which decreases monotonically with age. This has been done for the dense cloud core L183, for which the deuterium fractionation of diazenylium (N2H(+)) was used as a chemical clock to infer that the core has contracted rapidly (on a timescale of less than 700,000 years). Among astronomically observable molecules, the spin isomers of the deuterated trihydrogen cation, ortho-H2D(+) and para-H2D(+), have the most direct chemical connections to H2 (refs 8, 9, 10, 11, 12) and their abundance ratio provides a chemical clock that is sensitive to greater cloud core ages. So far this ratio has not been determined because para-H2D(+) is very difficult to observe. The detection of its rotational ground-state line has only now become possible thanks to accurate measurements of its transition frequency in the laboratory, and recent progress in instrumentation technology. Here we report observations of ortho- and para-H2D(+) emission and absorption, respectively, from the dense cloud core hosting IRAS 16293-2422 A/B, a group of nascent solar-type stars (with ages of less than 100,000 years). Using the ortho/para ratio in conjunction with chemical models, we find that the dense core has been chemically processed for at least one million years. The apparent discrepancy with the earlier N2H(+) work arises because that chemical clock turns off sooner than the H2D(+) clock, but both results imply that star-forming dense cores have ages of about one million years, rather than 100,000 years.

Context. Phosphorus-bearing compounds have only been studied in the circumstellar environments of the asymptotic giant branch star IRC +10 216 and the protoplanetary nebula CRL 2688, both carbon-rich objects, and the oxygen-rich red supergiant VY CMa. The current chemical models cannot reproduce the high abundances of PO and PN derived from observations of VY CMa. No observations have been reported of phosphorus in the circumstellar envelopes of oxygen-rich asymptotic giant branch stars. Aims. We aim to set observational constraints on the phosphorous chemistry in the circumstellar envelopes of oxygen-rich asymptotic giant branch stars, by focussing on the Mira-type variable star IK Tau. Methods. Using the IRAM 30 m telescope and the Submillimeter Array, we observed four rotational transitions of PN (J = 2−1, 3−2, 6−5, 7−6) and four of PO (J = 5/2−3/2, 7/2−5/2, 13/2−11/2, 15/2−13/2). The IRAM 30 m observations were dedicated line observations, while the Submillimeter Array data come from an unbiased spectral survey in the frequency range 279−355 GHz. Results. We present the first detections of PN and PO in an oxygen-rich asymptotic giant branch star and estimate abundances X(PN/H 2 ) ≈ 3 × 10 −7 and X(PO/H 2 ) in the range 0.5−6.0 × 10 −7 . This is several orders of magnitude higher than what is found for the carbon-rich asymptotic giant branch star IRC +10 216. The diameter ( 0. 7) of the PN and PO emission distributions measured in the interferometric data corresponds to a maximum radial extent of about 40 stellar radii. The abundances and the spatial occurrence of the molecules are in very good agreement with the results reported for VY CMa. We did not detect PS or PH 3 in the survey. Conclusions. We suggest that PN and PO are the main carriers of phosphorus in the gas phase, with abundances possibly up to several 10 −7 . The current chemical models cannot account for this, underlining the strong need for updated chemical models that include phosphorous compounds.

Context. V4332 Sgr experienced an outburst in 1994 whose observational characteristics in many respects resemble those of the eruption of V838 Mon in 2002. It has been proposed that these objects erupted because of a stellar-merger event. Aims. Our aim is to derive, from observational data, information on the present (10-15 yrs after the outburst) nature and structure of the object. Methods. We present and analyse a high-resolution (R ≈ 21 000) spectrum of V4332 Sgr obtained with the Subaru Telescope in June 2009. Various components (stellar-like continuum, atomic emission lines, molecular bands in emission) in the spectrum are analysed and discussed. We also investigate a global spectral energy distribution (SED) of the object mostly derived from broadband optical and infrared photometry. Results. The observed continuum resembles that of an ∼M 6 giant. The emission features (atomic and molecular) are most probably produced by radiative pumping. The observed strengths of the emission features strongly suggest that we only observe a small part of the radiation of the main object responsible for pumping the emission features. An infrared component seen in the observed SED, which can be roughly approximated by two blackbodies of ∼950 and ∼200 K, is ∼50 times brighter than the M 6 stellar component seen in the optical. This further supports the idea that the main object is mostly obscured for us. Conclusions. The main object in V4332 Sgr, an ∼M 6 (super)giant, is surrounded by a circumstellar disc, which is seen almost edgeon so the central star is obscured. The observed M 6 spectrum probably results from scattering the central star spectrum on dust grains at the outer edge of the disc.

Very Large Array observations of the extreme carbon star IRC+10216 at 7 mm wavelength with 40 milli-arcsec resolution resolve the object's radio emission, which forms an almost round uniform disk of 83 milli-arcsec diameter, corresponding to 11 AU (for an assumed distance of 130 pc). We find a brightness temperature of 1630 K for the radio photosphere. Since the emission is optically thick, we can directly estimate IRC+10216's average luminosity, which is 8600 L . This value is in excellent agreement with what is predicted from the period-luminosity relation for carbon-rich Miras. Assuming an effective temperature of 2750 K for IRC+10216, it implies an optical photospheric diameter of 3.8 AU. Our precise determination of IRC+10216's proper motion fits the picture presented by far-ultraviolet and far-infrared wavelength observations of its interaction region with the interstellar medium (its "astrosphere"): the star moves roughly in the direction expected from the morphology of the termination shock and its astrotail structures. Calculation of its three dimensional velocity and an analysis of the kinematics of its surrounding interstellar medium (ISM) suggest an appreciable relative velocity of 42 km s −1 , which is about half the value discussed in recent studies. This suggests a lower (time-averaged) mass loss rate and/or a higher ISM density than previously assumed.

Context. OGLE-2002-BLG-360 was discovered as a microlensing candidate by the OGLE-III project. The subsequent light curve, however, clearly showed that the brightening of the object could not have resulted from the gravitational microlensing phenomenon. These data allowed us to analyse the light curve of the object during its eruption, as well as the potential variability of its progenitor. In the archives of several infrared surveys, namely 2MASS, MSX, Spitzer, AKARI, WISE, and VVV, we found measurements of the object, which allowed us to study the spectral energy distribution (SED) of the object. We constructed a simple model of a star surrounded by a dusty envelope, which was used to interpret the observed SED. Results. Our analysis of the data clearly shows that OGLE-2002-BLG-360 was most probably a red transient, i.e. an object similar in nature to V838 Mon, whose eruption was observed in 2002. The SED in all phases, i.e. progenitor, eruption, and remnant, was dominated by infrared emission, which we interpret as evidence of dust formation in an intense mass outflow. Since 2009 the object has been completely embedded in dust. Conclusions. We suggest that the progenitor of OGLE-2002-BLG-360 was a binary, which had entered the common-envelope phase a long time (at least decades) before the observed eruption, and that the eruption resulted from the final merger of the binary components. We point out similarities between OGLE-2002-BLG-360 and CK Vul, whose eruption was observed in 1670−72, and this strengthens the hypothesis that CK Vul was also a red transient.

A spectral line survey of the oxygen-rich red supergiant VY Canis Majoris was made between 279 and 355 GHz with the Submillimeter Array. Two hundred twenty three spectral features from 19 molecules (not counting isotopic species of some of them) were observed, including the rotational spectra of TiO, TiO 2 , and AlCl for the first time in this source. The parameters and an atlas of all spectral features is presented. Observations of each line with a synthesized beam of ∼0. ′′ 9, reveal the complex kinematics and morphology of the nebula surrounding VY CMa. Many of the molecules are observed in high lying rotational levels or in excited vibrational levels. From these, it was established that the main source of the submillimeter-wave continuum (dust) and the high excitation molecular gas (the star) are separated by about 0. ′′ 15. Apparent coincidences between the molecular gas observed with the SMA, and some of the arcs and knots observed at infrared wavelengths and in the optical scattered light by the Hubble Space Telescope are identified. The observations presented here provide important constraints on the molecular chemistry in oxygen-dominated circumstellar environments and a deeper picture of the complex circumstellar environment of VY CMa.-4according to morphological type (Sect. 3.3); and discusses the continuum and location of the centers of molecular emission with respect to the peak of the continuum (Sect. 3.4). From an analysis of population diagrams, approximate rotational temperatures and column densities of eleven molecules were derived (Appendix B). A detailed discussion of the chemistry in the circumstellar gas and the structure of the outflow of VY CMa will be presented elsewhere. Observations and data reductionThe survey of VY CMa was obtained together with an AGB star IK Tau, whose observations will be presented elsewhere. The observations of VY CMa were made with the SMA in its extended configuration over ten nights during January and February of 2010 (see Table 1). In that configuration, unprojected baselines range in length from 44 to 226 m producing a synthesized beam with a full width at half maximum (FWHM) of typically 0. ′′ 9. On each night, observing began around 03:30 UT; IK Tau was observed for about two hours until VY CMa rose, at which time observations of IK Tau and VY CMa were interleaved for five hours until IK Tau set. After that, VY CMa was observed alone for two more hours. The phase center for IK Tau was α(2000) = 03 h 53 m 28.866 s , δ(2000) = 11 • 24 ′ 22.29. ′′ 2; for VY CMa α(2000) = 07 h 22 m 58.332 s , δ(2000) = −25 • 46 ′ 03.17. ′′ 2 was used. The online software Doppler-tracked VY CMa during the entire observation, the frequency scale for the IK Tau data was corrected offline to compensate for that. Nearby quasars were observed every 20 min for gain calibration. The quasar 0423-013 was used to calibrate IK Tau data, and 0730-116 was used for VY CMa. Titan was observed for flux calibration on the nights when it was separated from Saturn by several arcmin. On other night...