Search

We have performed a near-infrared photometric monitoring of 39 galactic young star clusters and star-forming regions, known as {\em NIP of Stars}, between the years 2009--2011, using the Swope telescope at Las Campanas Observatory (Chile) and the RetroCam camera. The primary objective of the campaign is to perform a census of photometric variability of such clusters and to discover massive eclipsing binary stars. In this work, we describe the general idea, the implementation of the survey, and the first preliminary results of some of the observed clusters. This monitoring program is complementary to the Vista Variables in the V\'ia L\'actea (VVV), as the brightest sources observed in NIP of Stars are saturated in VVV.

Supernova 1987A revealed that a blue supergiant (BSG) star can end its life as a core-collapse supernova (SN). SN 1987A and other similar objects exhibit properties that distinguish them from ordinary Type II Plateau (IIP) SNe, whose progenitors are believed to be red supergiants (RSGs). Similarities among 1987A-like events include a long rise to maximum, early luminosity fainter than that of normal Type IIP SNe, and radioactivity acting as the primary source powering the light curves. We present and analyze two SNe monitored by the Carnegie Supernova Project that are reminiscent of SN 1987A. Optical and near-infrared (NIR) light curves, and optical spectroscopy of SNe 2006V and 2006au are presented. These observations are compared to those of SN 1987A, and are used to estimate properties of their progenitors. Both objects exhibit a slow rise to maximum and light curve evolution similar to that of SN 1987A. At the earliest epochs, SN 2006au also displays an initial dip which we interpret as the signature of the adiabatic cooling phase that ensues shock break- out. SNe 2006V and 2006au are both found to be bluer, hotter and brighter than SN 1987A. Spectra of SNe 2006V and 2006au are similar to those of SN 1987A and other normal Type II objects, although both consistently exhibit expansion velocities higher than SN 1987A. Semi-analytic models are fit to the UVOIR light curve of each object from which physical properties of the progenitors are estimated. This yields ejecta mass estimates of about 20 solar masses, explosion energies of 2 - 3 x 10^51 erg, and progenitor radii of 75 - 100 solar radii for both SNe. The progenitors of SNe 2006V and 2006au were most likely BSGs with a larger explosion energy as compared to that of SN 1987A., Comment: 21 pages,15 figures, accepted for publication in A&A, 25 October 2011

A remarkable fraction of supernovae (SNe) have no obvious host galaxy. Two possible explanations are that (i) the host galaxy is simply not detected within the sensitivity of the available data or that (ii) the progenitor is a hypervelocity star that has escaped its parent galaxy. We use the Type IIb SN 2009Z as a prototype of case (i), an example of how a very faint (here Low Surface Brightness; LSB) galaxy can be discovered via the observation of a seemingly host-less SN. By identifying and studying LSB galaxies that host SNe related to the death of massive stars, we can place constraints on the stellar population and environment of LSB galaxies, which at present are poorly understood. From an HI spectrum, a redshift of z = 0.02513+-0.00001 and an HI mass of (2.96+-0.12) 10^9 M_sun are computed. This redshift is consistent with that obtained from optical emission lines of SN 2009Z. Furthermore, a gas mass fraction of f_g = 0.87+-0.04 is obtained, one of the highest fractions ever measured. The host galaxy shows signs of recently enhanced star formation activity with a far-UV derived extinction-corrected Star Formation Rate (SFR) of 0.44+-0.34 M_sun/yr. Based on the B-band luminosity we estimate an extinction-corrected metallicity following the calibration by Pilyugin (2001) of 12 + log(O/H) = 8.24+-0.70. The presence of a Type IIb SN in an LSB galaxy suggests, contrary to popular belief, that massive stars can be formed in this type of galaxies. Furthermore, our results imply that LSB galaxies undergo phases of small, local burst activity intermittent with longer phases of inactivity., Comment: 9 pages, 6 figures, accepted for publication in A&A, abstract abridged due to arXiv requirements

There are several ongoing massive-star (mostly of spectral type O) surveys that are significantly increasing the quality and quantity of the spectroscopic information about these objects. Here we discuss and present results for two of them, GOSSS and NoMaDS. We also discuss recent and future developments on the Galactic O-Star Catalog and announce the upcoming availability of Marxist Ghost Buster, an IDL code that attacks spectral classification (hence the name) by using an interactive comparison with spectral libraries., Comment: 7 pages, to appear in the proceedings of the conference in honor of Tony Moffat that took place at Lac Taureau in July 2011

In this paper we report the identification of two new Galactic O2 If*/WN6 stars (WR20aa and WR20c), in the outskirt of the massive young stellar cluster Westerlund 2. The morphological 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 intermediate O2 If*/WN6 spectral type. Based on a mosaic made from the 3.6 microns Spitzer IRAC 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 both 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 their birthplace by dynamical interacion with some other very massive objects, perhaps during some earlier stage of the cluster evolution., Comment: Published by MNRAS 25 JUL 2011

The periodic spectroscopic events in eta 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 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 eta Carinae with 5 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 Lsun) just before periastron reveals the presence of a very luminous transient source of extreme UV radiation emitted in the wind-wind collision (WWC) region. Clumps in the primary's 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 ne, Comment: Two-column style; 18 pages, 10 figures, and 1 table. Accepted for publication in ApJ

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 4650 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 M1sin^3 i = 78 \pm 8 Msun and M2sin^3 i = 66 \pm 7 Msun. 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., Comment: 5 pages, 5 figures. Letter accepted for publication in A&A

Using high-precision astrometric optical observations from the Walter Baade Magellan Telescope in conjunction with high-resolution very long baseline interferometric (VLBI) radio imaging with the Very Long Baseline Array (VLBA), we have located the core of the X-ray binary system XTE J1752-223. Compact radio emission from the core was detected following the state transition from the soft to the hard X-ray state. Its position to the south-east of all previously-detected jet components mandated a re-analysis of the existing VLBI data. Our analysis suggests that the outburst comprised at least two ejection events prior to 2010 February 26. No radio-emitting components were detected to the south-east of the core at any epoch, suggesting that the receding jets were Doppler-deboosted below our sensitivity limit. From the ratio of the brightness of the detected components to the measured upper limits for the receding ejecta, we constrain the jet speed to be greater than 0.66c and the inclination angle to the line of sight to be less than 49 degrees. Assuming that the initial ejection event occurred at the transition from the hard intermediate state to the soft intermediate state, an initial period of ballistic motion followed by a Sedov phase (i.e. self-similar adiabatic expansion) appears to fit the motion of the ejecta better than a uniform deceleration model. The accurate core location can provide a long time baseline for a future proper motion determination should the system show a second outburst, providing insights into the formation mechanism of the compact object., Comment: Accepted for publication in MNRAS. 8 pages, 3 figures

We present the first installment of a massive spectroscopic survey of Galactic O stars, based on new, high signal-to-noise ratio, R~2500 digital observations from both hemispheres selected from the Galactic O-Star Catalog of Ma\'iz Apell\'aniz et al. (2004) and Sota et al. (2008). The spectral classification system is rediscussed and a new atlas is presented, which supersedes previous versions. Extensive sequences of exceptional objects are given, including types Ofc, ON/OC, Onfp, Of?p, Oe, and double-lined spectroscopic binaries. The remaining normal spectra bring this first sample to 184 stars, which is close to complete to B=8 and north of delta = -20 and includes all of the northern objects in Ma\'iz Apell\'aniz et al. (2004) that are still classified as O stars. The systematic and random accuracies of these classifications are substantially higher than previously attainable, because of the quality, quantity, and homogeneity of the data and analysis procedures. These results will enhance subsequent investigations in Galactic astronomy and stellar astrophysics. In the future we will publish the rest of the survey, beginning with a second paper that will include most of the southern stars in Ma\'iz Apell\'aniz et al. (2004)., Comment: Accepted for publication in ApJS. 73 pages and 20 figures. Figure 19 is shown at a degraded resolution due to arXiv limitations. If interested in the high-resolution version, please contact the author

We present a detailed study of the kinematic and physical properties of the ionized gas in multiple knots of the blue compact dwarf galaxy Haro 15. Using echelle and long slit spectroscopy data, obtained with different instruments at Las Campanas Observatory, we study the internal kinematic and physical conditions (electron density and temperature), ionic and total chemical abundances of several atoms, reddening and ionization structure. Applying direct and empirical methods for abundance determination, we perform a comparative analysis between these regions and in their different components. On the other hand, our echelle spectra show complex kinematics in several conspicuous knots within the galaxy. To perform an in-depth 2D spectroscopic study we complete this work with high spatial and spectral resolution spectroscopy using the Integral Field Unit mode on the Gemini Multi-Object Spectrograph instrument at the Gemini South telescope. With these data we are able to resolve the complex kinematical structure within star forming knots in Haro 15 galaxy., Comment: 6 pages, 2 figures, IX Scientific Meeting of the Spanish Astronomical Society held on September 13-17, 2010, in Madrid, Spain

We present a massive spectroscopic survey of Galactic O stars, GOSSS, based on new, high signal-to-noise ratio, R~2500 blue-violet digital observations from both hemispheres. The sample size and selection criteria; the relationship between GOSSS, the Galactic O-Star Catalog (GOSC), and three sister surveys (OWN, IACOB, and Lucky Imaging); the current status; and our plans for the future are discussed. We also show some of our first results, which include the new Ofc category, two new examples of Of?p stars, a new atlas for O stars, and the introduction of the O9.7 type for luminosity classes III to V. Finally, our scientific objectives are discussed., Comment: 6 pages, to appear in Highlights of Spanish Astrophysics VI, Proceedings of the IX Scientific Meeting of the Spanish Astronomical Society held on September 13-17, 2010, in Madrid, Spain. M. R. Zapatero Osorio et al. (eds.)

We present new results from our search for Giant H\,{\sc ii} Regions in galaxies visible from the southern hemisphere. In this work we study two galaxies: NGC\,7479 and NGC\,6070. Using high-resolution spectra, obtained with different instruments at Las Campanas Observatory, we are able to resolve the emission-line profile widths and determine the intrinsic velocity dispersion of the ionised gas. We detect profile widths corresponding to supersonic velocity dispersions in the six observed H\,{\sc ii} regions. We find that all of them show at least two distinct kinematical components: a relatively narrow feature (between ~11 and ~22\kms) and a broader (between ~31 and ~77\kms) component. Two of the regions show a complex narrow profile in all ion lines, which can be further split into two components with different radial velocities. Whereas the wing broadening of the overall profile can be fitted with a low-intensity broad component for almost all profiles, in one region it was better reproduced by two separate shell-like wings. We have analysed the impact that the presence of multiple components has on the location of the H{\sc ii} regions in the $\log(L) - \log(\sigma)$ plane. Although the overall distribution confirms the presence of a regression, the precise location of the regions in the plane is strongly dependent on the components derived from the profile fitting., Comment: This manuscript has been accepted for publication in Monthly Notices of the Royal Astronomical Society Main Journal. 16 pages, 11 figures

We present a detailed study of the physical properties of the nebular material in multiple knots of the blue compact dwarf galaxy Haro 15. Using long slit and echelle spectroscopy, obtained at Las Campanas Observatory, we study the physical conditions (electron density and temperature), ionic and total chemical abundances of several atoms, reddening and ionization structure. The latter was derived by comparing the oxygen and sulphur ionic ratios to their corresponding observed emission line ratios (the eta and eta' plots) in different regions of the galaxy. Applying direct and empirical methods for abundance determination, we perform a comparative analysis between these regions., Comment: (Poster paper) 2 pages, 2 figures

Through comparison of pre- and post-explosion images obtained with the Wide Field and Planetary Camera 2 onboard the Hubble Space Telescope, we have isolated a supergiant star prior to explosion at nearly the same position as the high-luminosity SN II-P 2008cn. We provide evidence that this supergiant may well be the progenitor of the SN, although this identification is not entirely unambiguous due mainly to the distance to the host galaxy (NGC 4603), 33.3 Mpc. The progenitor candidate has a more yellow color than generally would be expected and, if a single star, would require that it exploded during a "blue loop" evolutionary phase. Nonetheless, we estimate an initial mass of Mini = 15 +/- 2 Msun for this star, which is within the expected mass range for SN II-P progenitors. The yellower color could also arise from the blend of two or more stars, such as a red supergiant hidden by a brighter, blue supergiant; or a massive, interacting binary system. Finally, if the yellow supergiant is not the progenitor, or is not a stellar blend or binary containing the progenitor, then we constrain any undetected progenitor star to be a red supergiant with Mini < 11 Msun, considering a physically more realistic scenario of explosion at the model endpoint luminosity for a rotating star. (ABRIDGED), Comment: 19 pages, 7 figures. Accepted for publication in ApJ (Oct. 12, 2009)

We use early-time photometry and spectroscopy of 12 Type II plateau supernovae (SNe IIP) to derive their distances using the expanding photosphere method (EPM). We perform this study using two sets of Type II supernova (SN II) atmosphere models, three filter subsets ($\{BV\}$, $\{BVI\}$, $\{VI\}$), and two methods for the host-galaxy extinction, which leads to 12 Hubble diagrams. We find that systematic differences in the atmosphere models lead to $\sim $50% differences in the EPM distances and to a value of ${\rm H_0}$ between 52 and 101 ${\rm km s^{-1} Mpc^{-1}}$. Using the $\{VI\}$ filter subset we obtain the lowest dispersion in the Hubble diagram, {${\rm \sigma_{\mu} = 0.32}$ mag}. We also apply the EPM analysis to the well-observed SN IIP 1999em. With the $\{VI\}$ filter subset we derive a distance ranging from 9.3 $\pm$ 0.5 Mpc to 13.9 $\pm$ 1.4 Mpc depending on the atmosphere model employed., Comment: Accepted for publication in the Astrophysical Journal

We report the results of a spectroscopic and polarimetric study of the massive, hydrogen-rich WN6h stars R144 (HD 38282 = BAT99-118 = Brey 89) and R145 (HDE 269928 = BAT99-119 = Brey 90) in the LMC. Both stars have been suspected to be binaries by previous studies (R144: Schnurr et al. 2008b; R145: Moffat 1989). We have combined radial-velocity (RV) data from these two studies with previously unpublished polarimetric data. For R145, we were able to establish, for the first time, an orbital period of 158.8 days, along with the full set of orbital parameters, including the inclination angle i, which was found to be i = 38 \pm 9 deg. By applying a modified version of the shift-and-add method developed by Demers et al. (2002), we were able to isolate the spectral signature of the very faint-line companion star. With the RV amplitudes of both components in R145, we were thus able to estimate their absolute masses. We find minimum masses M_WR sin^{3}i = (116 \pm 33) M_sol and M_O sin^{3}i = (48 \pm 20)$ M_sol for the WR and the O component, respectively. Thus, if the low inclination angle were correct, resulting absolute masses of the components would be at least 300 and 125 M_sol, respectively. However, such high masses are not supported by brightness considerations when R145 is compared to systems with known, very high masses such as NGC3603-A1 or WR20a. An inclination angle close to 90 degrees would remedy the situation, but is excluded by the currently available data. More and better data are thus required to firmly establish the nature of this puzzling, yet potentially very massive and important system. As to R144, however, the combined data sets are not sufficient to find any periodicity., Comment: 15 pages, 13 figures; accepted for publication by MNRAS

We report the results of an intense, spectroscopic survey of all 41 late-type, nitrogen-rich Wolf-Rayet (WR) stars in the Large Magellanic Cloud (LMC) observable with ground-based telescopes. This survey concludes the decade-long effort of the Montr\'eal Massive Star Group to monitor every known WR star in the Magellanic Clouds except for the 6 crowded WNL stars in R136, which will be discussed elsewhere. The focus of our survey was to monitor the so-called WNL stars for radial-velocity (RV) variability in order to identify the short- to intermediate-period ($P \la 200$ days) binaries among them. Our results are in line with results of previous studies of other WR subtypes, and show that the binary frequency among LMC WNL stars is statistically consistent with that of WNL stars in the Milky Way. We have identified four previously unknown binaries, bringing the total number of known WNL binaries in the LMC to nine. Since it is very likely that none but one of the binaries are classical, helium-burning WNL stars, but rather superluminous, hence extremely massive, hydrogen-burning objects, our study has dramatically increased the number of known binaries harbouring such objects, and thus paved the way to determine their masses through model-independent, Keplerian orbits. It is expected that some of the stars in our binaries will be among the most massive known. With the binary status of each WR star now known, we also studied the photometric and X-ray properties of our program stars using archival MACHO photometry as well as Chandra and ROSAT data. We find that one of our presumably single WNL stars is among the X-ray brightest WR sources known. We also identify a binary candidate from its RV variability and X-ray luminosity which harbours the most luminous WR star known in the Local Group., Comment: 25 pages, 11 figures; accepted for MNRAS

We are conducting a spectroscopic monitoring of O and WN -type stars in our Galaxy. In this work, we summarize some of our first results related to the search for radial-velocity variations indicative of orbital motion., Comment: 4 pages, to appear in the Boletin de la Asociacion Argentina de Astronomia, vol.50

We present the results of optical wavelength observations of the unusual SMC eclipsing binary system HD 5980 obtained in 1999 and 2004--2005. Radial velocity curves for the erupting LBV/WR object (star A) and its close WR-like companion (star B) are obtained by deblending the variable emission-line profiles of N IV and N V lines under the simplistic assumption that these lines originate primarily in the winds of star A and star B. The derived masses M_A=58--79 Mo and M_B=51--67 Mo, are more consistent with the stars' location near the top of the HRD than previous estimates. The presence of a wind-wind interaction region is inferred from the orbital phase-dependent behavior of He I P Cygni absorption components. The emission-line intensities continued with the declining trend previously seen in UV spectra. The behavior of the photospheric absorption lines is consistent with the results of Schweickhardt (2002) who concludes that the third object in the combined spectrum, star C, is also a binary system with P(starC)~96.5 days, e=0.83. The data used in this paper will be made publicly available for further analysis., Comment: 48 pages, 26 figures

Optical observations of the Type Ia supernova (SN Ia) 2005bl in NGC 4070, obtained from -6 to +66 d with respect to the B-band maximum, are presented. The photometric evolution is characterised by rapidly-declining light curves and red colours at peak and soon thereafter. With M_B,max = -17.24 the SN is an underluminous SN Ia, similar to the peculiar SNe 1991bg and 1999by. This similarity also holds for the spectroscopic appearance, the only remarkable difference being the likely presence of carbon in pre-maximum spectra of SN 2005bl. A comparison study among underluminous SNe Ia is performed, based on a number of spectrophotometric parameters. Previously reported correlations of the light-curve decline rate with peak luminosity and R(Si) are confirmed, and a large range of post-maximum Si II lambda6355 velocity gradients is encountered. 1D synthetic spectra for SN 2005bl are presented, which confirm the presence of carbon and suggest an overall low burning efficiency with a significant amount of leftover unburned material. Also, the Fe content in pre-maximum spectra is very low, which may point to a low metallicity of the precursor. Implications for possible progenitor scenarios of underluminous SNe Ia are briefly discussed., Comment: 24 pages, 24 figures, accepted for publication in MNRAS

A full description of the 5.5-yr low excitation events in Eta Carinae is presented. We show that they are not as simple and brief as previously thought, but a combination of two components. The first, the 'slow variation' component, is revealed by slow changes in the ionization level of circumstellar matter across the whole cycle and is caused by gradual changes in the wind-wind collision shock-cone orientation, angular opening and gaseous content. The second, the 'collapse' component, is restricted to around the minimum, and is due to a temporary global collapse of the wind-wind collision shock. High energy photons (E > 16 eV) from the companion star are strongly shielded, leaving the Weigelt objects at low ionization state for >6 months. High energy phenomena are sensitive only to the 'collapse', low energy only to the 'slow variation' and intermediate energies to both components. Simple eclipses and mechanisms effective only near periastron (e.g., shell ejection or accretion onto the secondary star) cannot account for the whole 5.5-yr cycle. We find anti-correlated changes in the intensity and the radial velocity of P Cygni absorption profiles in FeII 6455 and HeI 7065 lines, indicating that the former is associated to the primary and the latter to the secondary star. We present a set of light curves representative of the whole spectrum, useful for monitoring the next event (2009 January 11)., Comment: 16 pages, 7 EPS figures, accepted for publication on MNRAS

Extensive spectral observations of eta Carinae over the last cycle, and particularly around the 2003.5 low excitation event, have been obtained. The variability of both narrow and broad lines, when combined with data taken from two earlier cycles, reveal a common and well defined period. We have combined the cycle lengths derived from the many lines in the optical spectrum with those from broad-band X-rays, optical and near-infrared observations, and obtained a period length of 2022.7+-1.3 d. Spectroscopic data collected during the last 60 years yield an average period of 2020+-4 d, consistent with the present day period. The period cannot have changed by more than $\Delta$P/P=0.0007 since 1948. This confirms the previous claims of a true, stable periodicity, and gives strong support to the binary scenario. We have used the disappearance of the narrow component of HeI 6678 to define the epoch of the Cycle 11 minimum, T_0=JD 2,452,819.8. The next event is predicted to occur on 2009 January 11 (+-2 days). The dates for the start of the minimum in other spectral features and broad-bands is very close to this date, and have well determined time delays from the HeI epoch., Comment: 9 pages, 4 EPS figures, submitted to MNRAS

We report on optical and infrared observations of the anomalous X-ray pulsar (AXP) 1E 1048.1-5937, made during its ongoing X-ray flare which started in 2007 March. We detected the source in the optical I and near-infrared Ks bands in two ground-based observations and obtained deep flux upper limits from four observations, including one with the Spitzer Space Telescope at 4.5 and 8.0 microns. The detections indicate that the source was approximately 1.3--1.6 magnitudes brighter than in 2003--2006, when it was at the tail of a previous similar X-ray flare. Similar related flux variations have been seen in two other AXPs during their X-ray outbursts, suggesting common behavior for large X-ray flux variation events in AXPs. The Spitzer flux 1E 1048.1-5937 limits are sufficiently deep that we can exclude mid-infrared emission similar to that from the AXP 4U 0142+61, which has been interpreted as arising from a dust disk around the AXP. The optical/near-infrared emission from probably has a magnetospheric origin. The similarity in the flux spectra of 4U 0142+61 and 1E 1048.1-5937 challenges the dust disk model proposed for the latter., Comment: 5 pages, 1 figure, accepted by ApJ

We present extensive ugrizYHJK photometry and optical spectroscopy of SN 2005gj obtained by the SDSS-II and CSP Supernova Projects, which give excellent coverage during the first 150 days after the time of explosion. These data show that SN 2005gj is the second clear case, after SN 2002ic, of a thermonuclear explosion in a dense circumstellar environment. Both the presence of singly and doubly ionized iron-peak elements (FeIII and weak SII, SiII) near maximum light as well as the spectral evolution show that SN 2002ic-like events are Type Ia explosions. Independent evidence comes from the exponential decay in luminosity of SN 2005gj, pointing to an exponential density distribution of the ejecta. The interaction of the supernova ejecta with the dense circumstellar medium is stronger than in SN 2002ic: (1) the supernova lines are weaker; (2) the Balmer emission lines are more luminous; and (3) the bolometric luminosity is higher close to maximum light. The velocity evolution of the Halpha components suggest that the CSM around SN 2005gj is clumpy and it has a flatter density distribution compared with the steady wind solution, in agreement with SN 2002ic. An early X-ray observation with Chandra gives an upper-limit on the mass loss rate from the companion of < 2x10^{-4} Msun/yr., Comment: 63 pages, 16 figures, submitted to AJ

We report precipitable water vapor (PWV) measurements made at Las Campanas Observatory using optical spectra of H2O lines obtained with the Magellan echelle spectrograph, and calculated using a robust technique that is accurate to 5-10%. Calibration of the relationship between our PWV measurements and opacity values at 225 GHz was made possible by simultaneous tipping radiometer observations. Based on this calibration, we present Las Campanas Observatory winter-time precipitable water vapor statistics, measured using the tipping radiometer, during a two month campaign. The median value of 2.8 +- 0.3 mm is consistent with that measured at the nearby La Silla Observatory during the VLT site survey. We conclude that, in the Southern hemisphere winter months, we can expect good conditions for infrared observing (<~1.5 mm) approximately 10% of the time at Las Campanas Observatory., Comment: 14 pages, 5 tables, 9 figures, accepted by PASP in May 2007

We are using HST GO programs 10205, 10602, and 10898 to test the stellar upper mass limit in the solar vicinity by attempting to detect optical close companions, thus lowering the calculated evolutionary masses. We have observed with ACS/HRC all the known (as of early 2005) Galactic O2/3/3.5 stars. We also have observations with HST/FGS and ground-based spectroscopy from LCO and CASLEO. Here we discuss our results for Pismis 24 and HD 93129A., Comment: 1 page, to appear in Massive Stars: Fundamental Parameters and Circumstellar Interactions

Is there a stellar upper mass limit? Recent statistical work seems to indicate that there is and that it is in the vicinity of 150 solar masses. In this paper we use HST and ground-based data to investigate the brightest members of the cluster Pismis 24, one of which (Pismis 24-1) was previously inferred to have a mass greater than 200 solar masses, in apparent disagreement with that limit. We determine that Pismis 24-1 is composed of at least three objects, the resolved Pismis 24-1SW and the unresolved spectroscopic binary Pismis 24-1NE. The evolutionary zero-age masses of Pismis 24-1SW, the unresolved system Pismis 24-1NE, and the nearby star Pismis 24-17 are all approximately 100 solar masses, very large but under the stellar upper mass limit., Comment: 16 pages, 3 figures, accepted in ApJ, second astro-ph version reflects changes suggested by referee

We present extensive u'g'r'i'BVRIYJHKs photometry and optical spectroscopy of SN 2005hk. These data reveal that SN 2005hk was nearly identical in its observed properties to SN 2002cx, which has been called ``the most peculiar known type Ia supernova.'' Both supernovae exhibited high ionization SN 1991T-like pre-maximum spectra, yet low peak luminosities like SN 1991bg. The spectra reveal that SN 2005hk, like SN 2002cx, exhibited expansion velocities that were roughly half those of typical type Ia supernovae. The R and I light curves of both supernovae were also peculiar in not displaying the secondary maximum observed for normal type Ia supernovae. Our YJH photometry of SN 2005hk reveals the same peculiarity in the near-infrared. By combining our optical and near-infrared photometry of SN 2005hk with published ultraviolet light curves obtained with the Swift satellite, we are able to construct a bolometric light curve from ~10 days before to ~60 days after B maximum. The shape and unusually low peak luminosity of this light curve, plus the low expansion velocities and absence of a secondary maximum at red and near-infrared wavelengths, are all in reasonable agreement with model calculations of a 3D deflagration which produces ~0.25 M_sun of 56Ni., Comment: Accepted by PASP, to appear in April 2007 issue, 63 pages, 16 figures, 11 tables

Since the discovery, with the EINSTEIN satellite, of strong X-ray emission associated with HD93162 (=WR25), this object has been predicted to be a colliding-wind binary system. However, radial-velocity variations that would prove the suspected binary nature have yet to be found. We spectroscopically monitored this object to investigate its possible variability to address this discordance. We compiled the largest available radial-velocity data set for this star to look for variations that might be due to binary motion. We derived radial velocities from spectroscopic data acquired mainly between 1994 and 2006, and searched these radial velocities for periodicities using different numerical methods. For the first time, periodic radial-velocity variations are detected. Our analysis definitively shows that the Wolf-Rayet star WR25 is an eccentric binary system with a probable period of about 208 days., Comment: 7 pages, 4 figures, accepted by A+A

We report the discovery of a new O-type double-lined spectroscopic binary with a short orbital period of 1.4 days. We find the primary component of this binary, FO 15, to have an approximate spectral type O5.5Vz, i.e. a Zero-Age-Main-Sequence star. The secondary appears to be of spectral type O9.5V. We have performed a numerical model fit to the public ASAS photometry, which shows that FO 15 is also an eclipsing binary. We find an orbital inclination of ~ 80 deg. From a simultaneous light-curve and radial velocity solution we find the masses and radii of the two components to be 30 +/- 1 and 16 +/- 1 solar masses and 7.5 +/- 0.5 and 5.3 +/- 0.5 solar radii. These radii, and hence also the luminosities, are smaller than those of normal O-type stars, but similar to recently born ZAMS O-type stars. The absolute magnitudes derived from our analysis locate FO 15 at the same distance as Eta Carinae. From Chandra and XMM X-ray images we also find that there are two close X-ray sources, one coincident with FO 15 and another one without optical counterpart. This latter seems to be a highly variable source, presumably due to a pre-main-sequence stellar neighbour of FO 15., Comment: 11 pages, 9 figures, 3 tables. Accepted for publication in MNRAS. Higher resolution version available at http://lilen.fcaglp.unlp.edu.ar/papers2006.html

A detailed study of the Hourglass Nebula in the M8 star forming region is presented. The study is mainly based on recent subarcsec-resolution JHKs images taken at Las Campanas Observatory and complemented with archival HST images and longslit spectroscopy retrieved from the ESO Archive Facility. Using the new numerical code CHORIZOS, we estimate the distance to the earliest stars in the region to be 1.25 kpc. Infrared photometry of all the sources detected in the field is given. From analysis of the JHKs colour-colour diagrams, we find that an important fraction of these sources exhibit significant infrared excess. These objects are candidates to be low- and intermediate-mass pre-main sequence stars. Based on HST observations, the spatial distribution of gas, dust and stars in the region is analyzed. The morphological analysis of these images also reveals a rich variety of structures related to star formation (proplyds, jets, bow shocks), similar to those observed in M16 and M42, along with the detection of the first four Herbig-Haro objects in the region. Furthermore, a longslit spectrum obtained with NTT confirms the identification of one of them (HH 870) in the core of the Hourglass nebula, providing the first direct evidence of active star formation by accretion in M8., Comment: 22 pages, 15 figures, 3 tables, submitted to MNRAS. A preprint with high-resolution figures is available at http://www.dfuls.cl/~rbarba/arias_hourglass.pdf

We present optical, near-IR, and radio follow up of sixteen Swift bursts, including our discovery of nine afterglows and a redshift determination for three. These observations, supplemented by data from the literature, provide an afterglow recovery rate of 60% in the optical/near-IR, much higher than in previous missions (BeppoSAX, HETE-2, INTEGRAL, and IPN). The optical/near-IR afterglows of Swift events are on average 1.7 mag fainter at t=12 hr than those of previous missions. The X-ray afterglows are similarly fainter compared to those of pre-Swift bursts. In the radio the limiting factor is the VLA threshold and the detection rate for Swift bursts is similar to that for past missions. The redshift distribution of pre-Swift bursts peaked at z~1, whereas the five Swift bursts with measured redshifts are distributed evenly between 1.3 and 3.2. From these results we conclude that (i) the pre-Swift distributions were biased in favor of bright events and low redshift events, (ii) the higher sensitivity and accurate positions of Swift result in a better representation of the true burst redshift and brightness distributions (which are higher and dimmer, respectively), and (iii) as many as 1/3 of the bursts can be optically dark, as a result of a high redshift and/or dust extinction. We remark that the apparent lack of low redshift, low luminosity Swift bursts, and the lower event rate compared to pre-launch estimates (90 vs. 150 per year), are the result of a threshold that is similar to that of BATSE. In view of these inferences, afterglow observers may find it advisable to make significant changes in follow up strategies of Swift events. [abridged], Comment: Submitted to ApJ; 15 pages, 8 figures, 1 table

The Ninth Catalogue of Spectroscopic Binary Orbits (http://sb9.astro.ulb.ac.be) continues the series of compilations of spectroscopic orbits carried out over the past 35 years by Batten and collaborators. As of 2004 May 1st, the new Catalogue holds orbits for 2,386 systems. Some essential differences between this catalogue and its predecessors are outlined and three straightforward applications are presented: (1) Completeness assessment: period distribution of SB1s and SB2s; (2) Shortest periods across the H-R diagram; (3) Period-eccentricity relation., Comment: Accepte for publication in A&A, 6 pages, 6 figures

We present a new optical spectroscopic study of the O-type binary HD 165052 based on high- and intermediate-resolution CCD observations. We re-investigated the spectral classification of the binary components, obtaining spectral types of O6.5 V and O7.5 V for the primary and secondary, respectively, finding that both stars display weak C {\sc iii} $\lambda5696$ emission in their spectra. We also determined a radial-velocity orbit for HD 165052 with a period of 2.95510 $\pm$ 0.00001 d, and semiamplitudes of 94.8 and 104.7 $\pm$ 0.5 km s$^{-1}$, resulting in a mass ratio $Q = 0.9$. From a comparison with previous radial-velocity determinations, we found evidence of apsidal motion in the system. Several signatures of wind-wind collision, such as phase-locked variability of the X-ray flux and the Struve-Sahade effect, are also considered. It was also found that the reddening in the region should be normal, in contrast with previous determinations., Comment: 9 pages, 5 tables, 9 figures. Accepted by Monthly Notices

We present a method to calculate masses for components of both eclipsing and non-eclipsing binary systems as long as their apsidal motion rates are available. The method is based on the fact that the equation that gives the rate of apsidal motion is a supplementary equation that allows the computation of the masses of the components, if the radii and the internal structure constants of them can be obtained from theoretical models. For this reason the use of this equation makes the method presented here model dependent. We apply this method to calculate the mass of the components of the non-eclipsing massive binary system HD 93205 (O3V+O8V), which is suspected to be a very young system. To this end, we computed a grid of evolutionary models covering the mass range of interest, and taking the mass of the primary (M_1) as the only independent variable, we solve the equation of apsidal motion for M_1 as a function of the age of the system. The mass of the primary we find ranges from M_1= 60+-19 msun for ZAMS models, which sets an upper limit for M_1, down to M_1= 40+-9 msun for an age of 2 Myr. Accordingly, the upper limit derived for the mass of the secondary (M_2= Q M_1) is M_2= 25 msun is in very good agreement with the masses derived for other O8V stars occurring in eclipsing binaries., Comment: To be published in MNRAS, 7 pages, 8 figures

Optical spectroscopy of CPD -59 2635, one of the O-type stars in the open cluster Trumpler 16 in the Carina Nebula, reveals this star to be a double-lined binary system. We have obtained the first radial velocity orbit for this system, consisting of a circular solution with a period of 2.2999 days and semi amplitudes of 208 and 273 km/s. This results in minimum masses of 15 and 11 Msol for the binary components of CPD -59 2635, which we classified as O8V and O9.5V, though spectral type variations of the order of 1 subclass, that we identify as the Struve-Sahade effect, seem to be present in both components. From ROSAT HRI observations of CPD -59 2635 we determine a luminosity ratio log(L_x/L_bol)~ -7, which is similar to that observed for other O-type stars in the Carina Nebula region. No evidence of light variations is present in the available optical or X-rays data sets., Comment: 8 pages, 6 Figures, Accepted by MNRAS (April 2001)

A new high-quality set of orbital parameters for the O-type spectroscopic binary HD93205 has been obtained combining echelle and coude CCD observations. The radial velocity orbits derived from the HeII 4686 A (primary component) and HeI 4471 A (secondary component) absorption lines yield semiamplitudes of 133 +/- 2 and 314 +/- 2 km/s for each binary component, resulting in minimum masses of 31 and 13 Msol (q = 0.42). We also confirm for the binary components the spectral classification of O3V+O8V previously assigned. Assuming for the O8V component a ``normal'' mass of 22 - 25 Msol we would derive for the primary O3V a mass of ``only'' 52 - 60 Msol and an inclination of about 55 degrees for the orbital plane. We have also determined for the first time a period of apsidal motion for this system, namely 185 +/- 16 years using all available radial velocity data-sets of HD 93205 (from 1975 to 1999). Phase-locked variations of the X-ray emission of HD 93205 consisting of a rise of the observed X-ray flux near periastron passage, are also discussed., Comment: 11 pages, 8 Figures, Accepted by MNRAS (April 2001)

We present a V light curve of the eclipsing binary system HV 2543 (Sk-67 117) in the Large Magellanic Cloud based on CCD images acquired between the years 1995 and 1998. We have analysed this light curve and published radial velocity data, finding that this system is semidetached, with the secondary (less massive and less luminous component) filling its Roche lobe. From our analysis with the Wilson-Devinney code, we estimated the following masses and radii for the components of HV 2543: M1=25.63 +- 0.7, R1=15.54 +- 0.4, M2=15.63 +- 1.0 and R2=13.99 +- 0.4, in solar units. On the basis of B and V photometry of the field stars, we found that HV 2543 is member of an OB association, perhaps related to which the massive binary system Sk-67 105 belongs., Comment: 8 pages, 4 postscript figures, accepted for publication in A&A