R. H. Barbá

EARLY RESULTS FROM THE GALACTIC O-STAR SPECTROSCOPIC SURVEY: C III EMISSION LINES IN Of SPECTRA

On the basis of an extensive new spectroscopic survey of Galactic O stars, we introduce the Ofc category, which consists of normal spectra with C III {lambda}{lambda}4647-4650-4652 emission lines of comparable intensity to those of the Of defining lines N III {lambda}{lambda}4634-4640-4642. The former feature is strongly peaked to spectral type O5, at all luminosity classes, but preferentially in some associations or clusters and not others. The relationships of this phenomenon to the selective C III {lambda}5696 emission throughout the normal Of domain, and to the peculiar, variable Of?p category, for which strong C III {lambda}{lambda}4647-4650-4652 emission is a defining characteristic, are discussed. Magnetic fields have recently been detected on two members of the latter category. We also present two new extreme Of?p stars, NGC 1624-2 and CPD -28 deg. 2561, bringing the number known in the Galaxy to five. Modeling of the behavior of these spectral features can be expected to better define the physical parameters of both normal and peculiar objects, as well as the atomic physics involved.

BONA FIDE, STRONG-VARIABLE GALACTIC LUMINOUS BLUE VARIABLE STARS ARE FAST ROTATORS: DETECTION OF A HIGH ROTATIONAL VELOCITY IN HR CARINAE*

We report optical observations of the luminous blue variable (LBV) HR Carinae which show that the star has reached a visual minimum phase in 2009. More importantly, we detected absorptions due to Si IV lambdalambda4088-4116. To match their observed line profiles from 2009 May, a high rotational velocity of v{sub rot} approx = 150 +- 20 km s{sup -1} is needed (assuming an inclination angle of 30 deg.), implying that HR Car rotates at approx =0.88 +- 0.2 of its critical velocity for breakup (v{sub crit}). Our results suggest that fast rotation is typical in all strong-variable, bona fide galactic LBVs, which present S-Dor-type variability. Strong-variable LBVs are located in a well-defined region of the HR diagram during visual minimum (the LBV minimum instability strip). We suggest this region corresponds to where v{sub crit} is reached. To the left of this strip, a forbidden zone with v{sub rot}/v{sub crit}>1 is present, explaining why no LBVs are detected in this zone. Since dormant/ex LBVs like P Cygni and HD 168625 have low v{sub rot}, we propose that LBVs can be separated into two groups: fast-rotating, strong-variable stars showing S-Dor cycles (such as AG Car and HR Car) and slow-rotating stars withmorexa0» much less variability (such as P Cygni and HD 168625). We speculate that supernova (SN) progenitors which had S-Dor cycles before exploding (such as in SN 2001ig, SN 2003bg, and SN 2005gj) could have been fast rotators. We suggest that the potential difficulty of fast-rotating Galactic LBVs to lose angular momentum is additional evidence that such stars could explode during the LBV phase.«xa0less

NGC 1624-2: a slowly rotating, X-ray luminous Of?cp star with an extraordinarily strong magnetic field

This paper presents a first observational investigation of t he faint Of?p star NGC 1624-2, yielding important new constraints on its spectral and physical characteristics, rotation, magnetic field strength, X-ray emission and magnetospheric pro perties. Modeling the spectrum and spectral energy distribution, we conclude that NGC 1624-2 is a main sequence star of mass M≃ 30 M⊙, and infer an effective temperature of 35± 2 kK and log g = 4.0± 0.2. Based on an extensive time series of optical spectral observation s we report significant variability of a large number of spectral lines, and infer a unique period of 157.99± 0.94 d which we interpret as the rotational period of the star. We report the detec tion of a very strong - 5.35± 0.5 kG - longitudinal magnetic field h Bzi , coupled with probable Zeeman splitting of Stokes I profiles of metal lines confirming a surface field modulus h Bi of 14± 1 kG, consistent with a surface dipole of polar strength ∼ 20 kG. This is the largest magnetic field ever detected in an O-type star, and the first report of Zeeman splitting of Stoke s I profiles in such an object. We also report the detection of reversed Stokes V profiles associated with weak, high-excitation emission lines of Oiii, which we propose may form in the close magnetosphere of the star. We analyze archival Chandra ACIS-I X-ray data, inferring a very hard spectrum with an X-ray effi ciency log Lx/Lbol =−6.4, a factor of 4 larger than the canonical value for O-type sta rs and comparable to that of the young magnetic O-type starθ 1 Ori C and other Of?p stars. Finally, we examine the probable magnetospheric properties of the star, reporting in particular very strong magnetic confinement of the stellar wind, with η∗≃ 1.5× 10 4 , and a very large Alfven radius, RAlf = 11.4 R∗.

He II lambda-4686 in Eta Carinae: Collapse of the Wind-Wind Collision Region During Periastron Passage

The periodic spectroscopic events in ? Carinae are now well established and occur near the periastron passage of two massive stars in a very eccentric orbit. Several mechanisms have been proposed to explain the variations of different spectral features, such as an eclipse by the wind-wind collision (WWC) boundary, a shell ejection from the primary star or accretion of its wind onto the secondary. All of them have problems explaining all the observed phenomena. To better understand the nature of the cyclic events, we performed a dense monitoring of ? Carinae with five Southern telescopes during the 2009 low-excitation event, resulting in a set of data of unprecedented quality and sampling. The intrinsic luminosity of the He II ?4686 emission line (L ~ 310 L ?) just before periastron reveals the presence of a very luminous transient source of extreme UV radiation emitted in the WWC region. Clumps in the primarys wind probably explain the flare-like behavior of both the X-ray and He II ?4686 light curves. After a short-lived minimum, He II ?4686 emission rises again to a new maximum, when X-rays are still absent or very weak. We interpret this as a collapse of the WWC onto the surface of the secondary star, switching off the hard X-ray source and diminishing the WWC shock cone. The recovery from this state is controlled by the momentum balance between the secondarys wind and the clumps in the primarys wind.

The VLT-FLAMES Tarantula Survey: II. R139 revealed as a massive binary system

We report the discovery that R139 in 30 Doradus is a massive spectroscopic binary system. Multi-epoch optical spectroscopy of R139 was obtained as part of the VLT-FLAMES Tarantula Survey, revealing a double-lined system. The two components are of similar spectral types; the primary exhibits strong C III λ4650 emission and is classified as an O6.5 Iafc supergiant, while the secondary is an O6 Iaf supergiant. The radial-velocity variations indicate a highly eccentric orbit with a period of 153.9 days. Photometry obtained with the Faulkes Telescope South shows no evidence for significant variability within an 18 month period. The orbital solution yields lower mass limits for the components of M1 sin 3 i = 78 ± 8 M� and M2 sin 3 i = 66 ± 7 M� . As R139 appears to be the most massive binary system known to contain two evolved Of supergiants, it will provide an excellent test for atmospheric and evolutionary models.

A ~ 40 Year Variability Cycle in the Luminous Blue Variable/Wolf-Rayet Binary System HD 5980?

The massive Wolf-Rayet stellar system HD 5980 in the Small Magellanic Cloud entered a sudden and brief ~xa01-3 mag eruptive state in the mid-1990s. The cause of the instability is not yet understood, but mechanisms similar to those in luminous blue variables are suspected. Using a previously unreported set of spectroscopic data obtained in 1955-1967 and recently acquired optical and HST/STIS spectra, we find that (1) the brief eruptions of 1993 and 1994 occurred at the beginning of an extended (~ decades) high state of activity characterized by large emission-line intensities; (2) the level of activity is currently subsiding; and (3) another strong emission-line episode appears to have occurred between 1960 and 1965, suggesting the possibility that the long-term cyclical variability may be recurrent on a ~xa040 year timescale. These characteristics suggest the possible classification of HD 5980 as an S Doradus-type variable. The effects due to binary interactions in the system are discussed, and we tentatively suggest that the short duration and relatively hot spectral type (WN11/B1.5I) observed during maximum in the visual light curve may be attributed to these interactions.

Active Star Formation in the N11B Nebula in the Large Magellanic Cloud: A Sequential Star Formation Scenario Confirmed

The second largest H ii region in the Large Magellanic Cloud, N11B has been surveyed in the near-IR. We present JHKs images of the N11B nebula. These images are combined with CO (1 ! 0) emission-line data and with archival New Technology Telescope and Hubble Space Telescope WFPC2 optical images to address the star formation activity of the region. IR photometry of all the IR sources detected is given. We confirm that a second generation of stars is currently forming in the N11B region. Our IR images show the presence of several bright IR sources that appear to be located toward the molecular cloud as seen from the CO emission in the area. Several of these sources show IR colors with young stellar object characteristics, and they are prime candidates to be intermediate-mass Herbig Ae/Be stars. For the first time, an extragalactic methanol maser is directly associated with IR sources embedded in a molecular core. Two IR sources are found at 2 00 (0.5 pc) of the methanol maser reported position. Additionally, we present the association of the N11A compact H ii region to the molecular gas, where we find that the young massive O stars have eroded a cavity in the parental molecular cloud, typical of a champagne flow. The N11 region turns out to be a very good laboratory for studying the interaction of winds, UV radiation, and molecular gas. Several photodissociation regions are found.

Milky Way demographics with the VVV survey - II. Color transformations and near-infrared photometry for 136 million stars in the southern Galactic disk

1 Departamento de Física, Universidad de La Serena, 980 Benavente, La Serena, Chile e-mail: msoto@dfuls.cl 2 Instituto de Ciencias Astronómicas, del la Tierra y del Espacio (ICATE-CONICET), Av. España Sur 1512, J5402DSP San Juan, Argentina 3 Observatório Astronómico de Córdoba, Universidad Nacional de Córdoba, Laprida 854, x5000 BGR, Córdoba, Argentina 4 Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Vicuña Mackena 4860, Casilla 306, Santiago 22, Chile 5 Vatican Observatory, Vatican City State 00120, Italy 6 European Southern Observatory, 3107 Vitacura, Santiago, Chile 7 Department of Astrophysical Sciences, Princeton University, Princeton NJ 08544-1001, USA 8 The Milky Way Millennium Nucleus, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago, Chile 9 Departamento de Ciencia Fisicas, Universidad Andres Bello, Avda. Republica 252, Santiago, Chile 10 Centre for Astrophysics Research, Science and Technology Research Institute, University of Hertfordshire, Hatfield AL10 9AB, UK 11 Department of Astronomy and Physics, Saint Mary’s University, Halifax, Nova Scotia, B3K 5L3, Canada 12 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK 13 Astronomy Unit, School of Physics and Astronomy, Queen Mary University of London, Mile End Road, London, E1 4NS, UK 14 Departamento de Física y Astronomía, Universidad de Valparaíso, Av. Gran Bretaña 1111, Playa Ancha, Casilla 5030, Chile 15 Instituto de Astronomía Teórica y Experimental, CONICET, Laprida 922, 5000 Córdoba, Argentina 16 Departmento de Astronomía, Universidad de Concepción, Casilla 160-C, Concepción, Chile 17 Instituto de Astronomía, Universidad Católica del Norte, Av. Angamos 0610, Antofagasta, Chile 18 Atacama Large Millimeter Array, Alonso de Córdova 3107, Vitacura, Santiago, Chile

Two O2 If*/WN6 stars possibly ejected from the massive young Galactic cluster Westerlund 2

In this paper we report the identification of two new Galactic O2If*/WN6 stars (WR20aa and WR20c),ontheoutskirtsofthemassiveyoungstellarclusterWesterlund2.Themorphological similarity between the near-infrared spectra of the new stars with that of WR20a and WR21a (two of the most massive binaries known to date) is remarkable, indicating that probably they are also very massive stars. New optical spectroscopic observations of WR20aa suggest an intermediateO2If*/WN6spectraltype.Basedonamosaicmadefromthe3.6µmSpitzerIRAC images of the region including part of the RCW49 complex, we studied the spatial location of the new emission line stars, finding that WR20aa and WR20c are well displaced from the centre of Westerlund 2, being placed at ≈36 pc (15.7 arcmin) and ≈58 pc (25.0 arcmin), respectively, for an assumed heliocentric distance of 8 kpc. Also, very remarkably, a radius vector connecting the two stars would intercept the Westerlund 2 cluster exactly at the place where its stellar density reaches a maximum. We consequently postulate a scenario in which WR20aa and WR20c had a common origin somewhere in the cluster core, being ejected from theirbirthplacebydynamicalinteractionwithsomeotherverymassiveobjects,perhapsduring some earlier stage of the cluster evolution.

ON THE MULTIPLICITY OF THE ZERO-AGE MAIN-SEQUENCE O STAR HERSCHEL 36

We present the analysis of high-resolution optical spectroscopic observations of the zero-age main-sequence O star Herschel 36 spanning six years. This star is definitely a multiple system, with at least three components detected in its spectrum. Based on our radial-velocity (RV) study, we propose a picture of a close massive binary and a more distant companion, most probably in wide orbit about each other. The orbital solution for the binary, whose components we identify as O9 V and B0.5 V, is characterized by a period of 1.5415 {+-} 0.0006 days. With a spectral type O7.5 V, the third body is the most luminous component of the system and also presents RV variations with a period close to 498 days. Some possible hypotheses to explain the variability are briefly addressed and further observations are suggested.