V. M. Larionov

SN 2005cs in M51 – II. Complete evolution in the optical and the near-infrared

We present the results of the one-year long observational campaign of the type II plateau SN 2005cs, which exploded in the nearby spiral galaxy M51 (the Whirlpool galaxy). This extensive data set makes SN 2005cs the best observed low-luminosity, ^(56)Ni-poor type II plateau event so far and one of the best core-collapse supernovae ever. The optical and near-infrared spectra show narrow P-Cygni lines characteristic of this SN family, which are indicative of a very low expansion velocity (about 1000 km s^(−1) ) of the ejected material. The optical light curves cover both the plateau phase and the late-time radioactive tail, until about 380 d after core-collapse. Numerous unfiltered observations obtained by amateur astronomers give us the rare opportunity to monitor the fast rise to maximum light, lasting about 2 d. In addition to optical observations, we also present near-infrared light curves that (together with already published ultraviolet observations) allow us to construct for the first time a reliable bolometric light curve for an object of this class. Finally, comparing the observed data with those derived from a semi-analytic model, we infer for SN 2005cs a ^(56)Ni mass of about 3 × 10^(−3) M⊙, a total ejected mass of 8–13 M⊙ and an explosion energy of about 3 × 10^(50) erg .

On the population of galactic Luminous Blue Variables

We report the first results of a long term infrared monitoring campaign of known and candidate galactic Luminous Blue Variables (LBVs). In particular, we are able to confirm the LBV nature of G24.73+0.69, a luminous mid-B supergiant associated with a dusty ejection nebula. We find that prior to 2003 September G24.73+0.69 exhibited low amplitude (∆JHK ∼ 0.4 mag) variability, but in the ∼200 day period between 2003 September-2004 April it abruptly brightened by ∼0.7 mag in the broadband J filter. Subsequently, a further ∼0.4 mag increase was observed between 2004 April-October, resulting in an overall difference of ∼1.1 mag between (current) photometric mimimum and maximum; similar variability also being observed in the H and K bands. In light of the numerous recent IR studies of the galactic hot star population we also compile an updated census of confirmed and candidate galactic LBVs, reporting 12 and 23 members respectively for each class. Finally, we utilise this new census to construct an H-R diagram for the galactic LBV population, resulting in a striking confirmation of the LBV-minimum light strip.

A third red supergiant rich cluster in the Scutum-Crux arm

Aims. We aim to characterise the properties of a third massive, red supergiant dominated galactic cluster. Methods. To accomplish this we utilised a combination of near/mid- IR photometry and spectroscopy to identify and classify the properties of cluster members, and statistical arguments to determine the mass of the cluster. Results. We found a total of 16 strong candidates for cluster membership, for which formal classification of a subset yields spectral types from K3–M4 Ia and luminosities between log(L/L� ) ∼ 4.5–4.8 for an adopted distance of 6 ± 1 kpc. For an age in the range of 16–20 Myr, the implied mass is 2–4×10 4 M� , making it one of the most massive young clusters in the Galaxy. This discovery supports the hypothesis that a significant burst of star formation occurred at the base of Scutum-Crux arm between 10–20 Myr ago, yielding a

Dusty ring nebulae around new candidate Luminous Blue Variables

We report on the discovery of a further two ring nebulae in the Midcourse Space Experiment (MSX) Galactic Plane Survey; G24.73+0.69 and G26.47+0.02. Morphologically, both appear similar to the nebulae found around the Luminous Blue Variable (LBV) candidates G79.29+0.46 and Wra 17-96. A central, unresolved point source was identified in both cases - positional coincidence with the star StRS 237 was found for G26.47+0.02, while no optical counterpart could be identified for G24.73+0.69. However, subsequent near IR broadband imaging of the G24.73+0.69 field identified a very red - (J − K) ∼ 2 mag - stellar counterpart to the central object. Near-IR spectroscopy of both objects reveal rich emission line spectra dom- inated by H uf769 ,H euf769 and low excitation metals, suggesting classification as luminous B supergiants and revealing a striking superficial similarity to the other MSX ring sources and known LBVs. We utilised a NLTE model atomsphere code to model the K band spectra and near-IR spectral energy distributions of the central stars in order to determine their physical parameters. Adopting a distance, d = 5.2 kpc to G24.73+0.69 yields a temperature, T = 12 kK, luminosity, log (L/L� ) = 5.6 and mass loss rate, u M = 1 × 10 −5 Myr −1 . G26.47+0.02 appears to be a more extreme object; adopting d = 6.5 kpc results in T = 17 kK, log (L/L� ) = 6.0 and u M = 9 × 10 −5 Myr −1 , placing it at the Humphreys-Davidson limit for massive stellar objects. Analysis of the spatially resolved mid-IR fluxes of both objects reveal extended periods of enhanced mass loss, resulting in comparatively low mass nebulae, with chemistries dominated by O-rich dust (with a population of small Fe grains existing co-spatially with the silicate dust). Comparison to the other MSX ring nebulae sources reveals a homogeneous group of objects, with both stellar and nebular properties consistent with known LBVs. With both spectroscopic and/or photometric variability observed for those sources with multiepoch observations, we propose a close affinity between both classes of object and suggest that long term monitoring of the MSX sources will reveal them to be bona fide LBVs.

Bolometric luminosity variations in the luminous blue variable AFGL2298

Aims. We characterise the variability in the physical properties of the luminous blue variable AFGL 2298 (IRAS 18576+0341) between 1989−2008. Methods. In conjunction with published data from 1989−2001, we have undertaken a long term (2001−2008) near-IR spectroscopic and photometric observational campaign for this star and utilise a non-LTE model atmosphere code to interpret these data. Results. We find AFGL 2298 to have been highly variable during the two decades covered by the observational datasets. Photometric variations of ≥1.6 mag have been observed in the JHK wavebands; however, these are not accompanied by correlated changes in near-IR colour. Non-LTE model atmosphere analysis of 4 epochs of K band spectroscopy obtained between 2001−7 suggests that the photometric changes of AFGL 2298 were driven by expansion and contraction of the stellar photosphere accompanied by comparatively small changes in the stellar temperature (ΔT∗ ∼ 4.5 kK). Unclumped mass loss rates throughout this period were modest and directly comparable to those of other highly luminous (candidate) LBVs. However, the main finding of this analysis was that the bolometric luminosity of AFGL 2298 appears to have varied by at least a factor of ∼2 between 1989−2008, with it being one of the most luminous stars in the Galaxy during maximum. Comparison to other LBVs that have undergone non bolometric luminosity conserving “eruptions” shows such events to be heterogeneous, with AFGL 2298 the least extreme example. These results – and the diverse nature of both the quiescent LBVs and associated ejecta – may offer support to the suggestion that more than one physical mechanism is responsible for such behaviour.

On the radio emitting high mass X-ray binary LS 5039

We present new optical { near{IR spectroscopic and photometric observations of the newly discovered galactic microquasar LS 5039, which indicate a classication for the mass donor in the system of O6.5V((f)). Optical spectroscopy and photometry shows no variability over a timescale of years, and we nd no evidence of modulation by, or emission from the compact companion in these data. However signicant photometric variability (0:4 mag) is present in the H and K bands between 1995{2000. Such variability has been observed in other radio bright X-ray binaries where it has been attributed to synchrotron emission from the jet. However, given the non{thermal spectral index of the radio emission in LS 5039 this explanation appears unlikely, predicting a near{IR flux3 orders of magnitude too small to contribute signicantly at such wavelengths. Nightly optical photometry over a 21 day period between 2000 May{June reveals variability at a level of a few hundredths of a magnitude, with no periodicity or long term trend visible. Likewise, while the radio lightcurves show moderate variability (20 per cent of the mean flux density) we nd no evidence of periodic modulation { Monte Carlo simulations constrain any such periodic variability to <4 per cent modulation at 2.25 GHz. The dierences in behaviour between LS 5039 and Cygnus X-1 { the most closely related radio emitting High Mass X-ray Binary { are likely to be a result of the weaker stellar wind and probable greater orbital separation of LS 5039 compared to Cyg X-1.

On the Nature of EXor Accretion Events: An Infrequent Manifestation of a Common Phenomenology?

We present the results of a comparison between classical and newly identified EXor based on literature data and aimed at recognizing possible differences or similarities between the categories. Optical and near-IR two-color diagrams, modalities of fluctuations, and derived values of the mass accretion rates are indicative of strong similarities between the two samples. We demonstrate how the difference between the outburst and the quiescence spectral energy distribution of all EXor can be well fitted with a single blackbody, as if an additional thermal component appears during the outbursting phase. Temperatures of this additional component span between 1000 and 4500 K, while the radii of the emitting regions (assumed to be a uniform disk) span between 0.01 and 0.1 AU, sizes typical of the inner portions of the circumstellar disk. Spots persisting up to 50% of the outburst duration, not exceeding 10% of the stellar surface, and with temperatures compatible with the EXor mass accretion rates, are able to account for both the appearance of the additional thermal component and the dust sublimation in the inner structures of the disk. We also compare the EXor events with the most significant color and magnitude fluctuations of active T Tauri stars finding that (1) burst accretion phenomena should also be important for this latter class and (2) EXor events could be more frequent than those accidentally discovered. A remarkable case is that of the source V2493 Cyg, a T Tauri star recently identified as a strong outbursting object: New optical and near-IR photometric and spectroscopic data are presented in an attempt to clarify its EXor or FUor nature.

Discovery of the heavily obscured supernova 2002cv

Universita` di Roma Tor Vergata, Roma, ItalyReceived 1 June 2002, Accepted 1 June 2002Abstract. On the 13th of May 2002, supernova 2002cv was discovered using a near-infrared camera working at the AZT-24 1.1m telescope at Campo Imperatore (AQ-Italy). After theinfrared detection a simultaneous photometric follow-up wasstarted at optical wavelengths. The preliminary results confirm a heavily obscured object with a V − K color not lower than 6magnitudes, making SN 2002cv the most reddened supernova ever observed. This finding, along with the recent discovery ofanother obscured supernova, suggests a critical revision of the rates known to date. The estimate of the visual extinction andthe light curves are provided here. These latter indicate that our SN 2002cv observations are the earliest available for a type-Iasupernova at IR wavelengths.Key words. supernovae: general – supernovae: individual: SN2002cv – I nfrared: galaxies

Optical and NIR observations of the afterglow of GRB 020813

We present optical and near-infrared (NIR) photometry of the bright afterglow ofxa0GRBu2009020813. Our data span fromxa03xa0hours to 4xa0days after the GRB event. A rather sharp achromatic break is present in the light curve, 14xa0hours after the trigger. In the framework of jetted fireballs, this break corresponds to a jet half-opening angle ofxa0

Confirmation of the Luminous Blue Variable nature of AFGL 2298

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