Observations of V838 Mon in the CO rotational lines

We investigate the structure of a field around the position of V838 Mon as seen in the lowest CO rotational transitions. We also measure and analyse emission in the same lines at the position of V838 Mon.Observations have primarily been done in the CO J = 2-1 and J = 3-2 lines using the KOSMA telescope. A field of 3.4 squared degrees has been mapped in the on-the-fly mode in these transitions. Longer integration spectra in the on-off mode have been obtained to study the emission at the position of V838 Mon. Selected positions in the field have also been observed in the CO J = 1-0 transition using the Delingha telescope.In the observed field we have identified many molecular clouds. They can be divided into two groups from the point of view of their observed radial velocities. One, having V(LSR) in the range 18-32 km/s, can be identified with the Perseus Galactic arm. The other one, having V(LSR) between 44-57 km/s, probably belongs to the Norma-Cygnus arm. The radial velocity of V838 Mon is within the second range but the object does not seem to be related to any of the observed clouds. We did not find any molecular buble of a 1 degree dimension around the position of V838 Mon claimed in van Loon et al. An emission has been detected at the position of the object in the CO J = 2-1 and J = 3-2 transitions. The emission is very narrow (FWHM ~ 1.2 km/s) and at V(LSR) = 53.3 km/s. Our analysis of the data suggests that the emission is probably extended.Comment: paper accepted in A&

V4332 Sagittarii revisited

The eruption of V4332 Sgr discovered in February 1994 shows striking similarities to that of V838 Mon started in January 2002. The nature of these eruptions is, however, enigmatic and unclear. We present new photometric and spectroscopic data on V4332 Sgr obtained in April-May 2003 at the SAAO. The obtained spectrum shows an unusual emission-line component superimposed on an early M-type stellar spectrum. The emission-line spectrum is of very low excitation and is dominated by lines from neutral elemets (NaI, FeI, CaI) and molecular bands (TiO, ScO, AlO). We also analyse all the observational data, mainly photometric measurements, available for V4332 Sgr. This allows us to follow the evolution of the effective temperature, radius and luminosity of the object since February 1994 till 2003. We show that the observed decline of V4332 Sgr can be accounted for by a gravitational contraction of an inflated stellar envelope. The combined optical and infrared photometry in 2003 shows that apart from the M-type stellar component there is a strong infrared excess in the KLM bands. This excess was absent in the 2MASS measurements done in 1998 but was probably starting to appear in K in 1999 when the object was observed in the DENIS survey. We interpret the results in terms of a stellar merger scenario proposed by Soker & Tylenda. The infrared excess is likely to be due to a disc-like structure which is either of protostellar nature or has been produced during the 1994 eruption and stores angular momentum from the merger event.Comment: 11 pages, 5 figures, accepted in Astronomy & Astrophysic

A model of an expanding giant that swallowed planets for the eruption of V838 Monocerotis

In early 2002 V838 Monocerotis had an extraordinary outburst whose nature is still unclear. The optical light curve showed at least three peaks and imaging revealed a light echo around the object - evidence for a dust shell which was emitted several thousand years ago and now reflecting light from the eruption. Spectral analysis suggests that the object was relatively cold throughout the event, which was characterized by an expansion to extremely large radii. We show that the three peaks in the light curve have a similar shape and thus it seems likely that a certain phenomenon was three times repeated. Our suggestion that the outburst was caused by the expansion of a red giant, followed by the successive swallowing of three relatively massive planets in close orbits, supplies a simple explanation to all observed peculiarities of this intriguing object.Comment: 5 pages, 1 LaTex file, 2 .eps figures, accepted for publication in MNRA

On the progenitor of V838 Monocerotis

We summarize and analyze the available observational data on the progenitor and the enviroment of V838 Mon. From the available photometric data for the progenitor of V838 Mon we exclude the possibility that the object before eruption was an evolved red giant star (AGB or RGB star). We find that most likely it was a main sequence or pre-main sequence star of ~ 5-10 M_sun. From the light echo structure and evolution we conclude that the reflecting dust is of interstellar nature rather than blown by V838 Mon in the past. We discuss the IRAS and CO data for interstellar medium observed near the position of V838 Mon. Several interstellar molecular regions have radial velocities similar to that of V838 Mon, so dust seen in the light echo might be related to one of them.Comment: 12 pages, 7 figures, accepted for publication in Astronomy & Astrophysic

Inhibition of diacylglycerol–sensitive TRPC channels by synthetic and natural steroids

TRPC channels are a family of nonselective cation channels that regulate ion homeostasis and intracellular Ca2+ signaling in numerous cell types. Important physiological functions such as vasoregulation, neuronal growth, and pheromone recognition have been assigned to this class of ion channels. Despite their physiological relevance, few selective pharmacological tools are available to study TRPC channel function. We, therefore, screened a selection of pharmacologically active compounds for TRPC modulating activity. We found that the synthetic gestagen norgestimate inhibited diacylglycerol-sensitive TRPC3 and TRPC6 with IC50s of 3–5 µM, while half-maximal inhibition of TRPC5 required significantly higher compound concentrations (>10 µM). Norgestimate blocked TRPC-mediated vasopressin-induced cation currents in A7r5 smooth muscle cells and caused vasorelaxation of isolated rat aorta, indicating that norgestimate could be an interesting tool for the investigation of TRP channel function in native cells and tissues. The steroid hormone progesterone, which is structurally related to norgestimate, also inhibited TRPC channel activity with IC50s ranging from 6 to 18 µM but showed little subtype selectivity. Thus, TRPC channel inhibition by high gestational levels of progesterone may contribute to the physiological decrease of uterine contractility and immunosuppression during pregnancy