Integrated photometric properties of magellanic cloud star clusters

Integrated CCD BVR photometric measurements of Magellanic Cloud (MC) star clusters are described and summarized. The integrated colour-magnitude diagrams and colour-age relations for these systems imply that (a) the colour distribution of MC clusters is distinctly bi-modal (although this bi-modality is not simply explained as a distinction between young and old clusters), and (b) the MCs are probably not forming as many (if any) extremely massive clusters at the present as they did early in their lifetimes (i.e., 10 Gyr ago). Structurally, the MC clusters are seen to be intermediate between galactic globular and open clusters and their radial surface brightness profiles can generally be adequately fitted to single-mass King (1966) models (some exceptions do occur, however). Although the distribution of the derived structural parameters of young and old MC clusters are similar, they differ significantly from the distribution of structural parameters observed in intermediate-age clusters, suggesting that these structural properties do not evolve monotonically with time.Visiting astronomer at the Cerro Tololo Interamerican Observatory, National Optical Astronomy Observatories, operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.     

Models ofHii regions from recombination line observations

In order to study the ionized gas with low electron density the H159 and H200 radio recombination lines (v = 1.62 GHz) atl = 30°5 andl = 31°0 in the galactic plane, observed with the NRAO 43 m radiotelescope, are analyzed. The profiles show the LTE/ intensity ratio for the more distant component of the profiles ( _LSR = 100 km s^–1) (Cersosimo and Onello, 1991).To derive the electron density and temperature of the emitting gas a new interpretation of the radio recombination lines is made. We suppose that the emission originates in a superposition of ionized gas layers with different densities along the line of sight. The number of layers in the model is equal to the numbers of different order transitions observed. By solving an equations set, the contribution of different components can be calculated. The method is used to estimate the electron density and temperature of the gas. Eleven models of two non-LTE components are considered. The photon flux required to ionize the regions are calculated and the results are compared with previous observations obtained in the region at 3 cm (H85, H87, H88 lines) (Lockman, 1989).Our results suggest that the necessary photon flux to ionize the extended envelopes of the regions is at least one order of magnitude larger than that needed for ionizing the core of the regions.Member of the Carrera del Investigador Científico y Tecnológico del Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) from Argentina.Also Instituto Argentino de Radioastronomia.     

Hubble Space Telescope observations of magellanic cloud planetary nebulae: Stellar winds

Narrow-band [OIII] 500.7 nm images and ultraviolet spectrophotometry are obtained for 20 planetary nebulae (PNe) in the Magellanic Clouds using the Hubble Space Telescope (HST). Four objects show P Cygni-like features in the ultraviolet HST data, and/or broad emission complexes near the HeII 468.6 nm and CIV 580.6 nm lines in ground-based spectra. All objects are of excitation class four or lower, and all are compact and dense compared to other objects in the sample. The likelihood of detecting ultraviolet P Cygni-like profiles in future HST spectroscopy of other objects is discussed.     

AGB evolution in the large magellanic cloud

We review observations and theoretical studies of the evolution of massive asymptotic giant branch stars in the Magellanic Clouds. Recent results support the hypothesis that AGB is truncated, probably through mass loss, before these stars can attain the theoretically predicted maximum luminosity. In particular, IRAS observations of the LMC provide little evidence for the presence of highly obscured cocoon stars.     

Global photometric analysis of Galactic HII regions

Total infrared fluxes are estimated for 99 HII regions around massive stars. The following wavebands have been used for the analysis: 8 and 24 μm, based on data from the Spitzer Space Telescope(IRAC and MIPS, respectively); 70, 160, 250, 350 and 500 μm, based on data from the Herschel Space Observatory(PACS and SPIRE). The estimated fluxes are used to evaluate the polycyclic aromatic hydrocarbon(PAH) mass fraction(qPAH) and the intensity of ultraviolet emission in the studied objects.It is shown that the PAH mass fraction, qPAH, is much lower in these objects than the average Galactic value, implying effective destruction of aromatic particles in HII regions. Estimated radiation field intensities(U) are close to those derived for extragalactic HII complexes. Color indices [F_(24)/F_8], [F_(70)/F_(24)],[F_(160)/F_(24)] and [F_(160)/F_(70)] are compared to criteria proposed to distinguish between regions of ionized hydrogen and planetary nebulae. Also, we relate our results to analogous color indices for extragalactic complexes of ionized hydrogen.     

Period-luminosity relation for classical cepheids of the large magellanic cloud

Byurakan Astrophysical Observatory. Translated from Astrofizika, Vol. 34, No. 2, pp. 199–204, March–April, 1991.     

A giant Hii ring and energetic stellar winds in the large magellanic cloud

A large ring, 50 pc diameter, of H+[Nii] emission in the LMC has been investigated using several instruments. It is suggested that stellar winds from O and B stars could play a vital role in the formation of the structures revealed.     

Far UV extinction and the interstellar 4430 Å band in the large magellanic cloud

The central depths of the interstellar 4430 Å band and far UV extinction for a sample of reddened LMC members are presented here.     

Evolution of the optical spectrum of SN 1987a in the large magellanic cloud

The evolution of the spectrum of SN1987a is traced from 1987 February 26 to March 31. Based on the low-resolution spectroscopic data we identify the lines of H, He I, Na I, Fe II, Sc II, Ca II which are known to be present in Type II Supernovae, and also present evidence for the existence of lines of Mg I, Ca_I, O I, and N I. We discuss the evolution of the Hα profile, and draw attention to its complex structure around March 30. Close to the rest wavelength of Ha a double-peaked structure appeared in the profile with a peak-to-peak separation of ∼ 1400 km s⁻¹, suggestive of an expanding shell or disc of gas. Using the available broadband photometric information, we also trace the evolution of the photosphere of SN1987a assuming that it radiates like a supergiant.     

On the structure of the ‘red’ globular cluster NGC 1806 in the large magellanic cloud

A structural study of the old globular cluster NGC 1806 in the LMC has been carried out by star counts onB- andV-ESO 3.6 m telescope plates with three different limiting magnitude levels. The star density distribution was obtained directly from the surface strip count function with the Plummer formalism and the generalized Schuster law according to Lohmann. This yields beside the central density the structural parametern and the characteristic length parameterR ₀ for each individual colour and magnitude level.The results show that the blue stellar content of NGC 1806 — the horizontal branch stars — is more concentrated towards the cluster center than the red giant and subgiant objects. Also such a dynamical mass segregation is observed for the red giants compared with the subgiants.Based on observations collected at the European Southern Observatory, La Silla, Chile.     

An atlas of the optical spectrum of supernova 1987A in the large magellanic cloud

Photographic spectra of SN1987A in the LMC have been obtained from 1987 February 25 to 1988 June 30. Microdensitometer tracings of these have been reduced to intensity and corrections for instrumental response have been applied to the spectra. This paper presents these data in an atlas format, discusses the reduction procedures in detail, and presents radial velocity measurements of selected lines in the spectra     

Polarimetric and photometric observations of the star m cephei

The results of photometric and polarimetric observations of the star Μ Cep at Byurakan Observatory are presented. Some interesting correlations between the parameters of the star’s brightness variation and the degree of polarization of the light are obtained. It is suggested that the recorded rapid changes in the degree of polarization may result from Μ Cep being a double star. Translated from Astrofizika, Vol. 43, No. 2, pp. 219-228, April–June, 2000.     

Spectral and photometric observations of the star Y Ori

Data are presented from a spectral and photometric study of the long-period variable star Y Ori, which we have classified as a type M7IIIe near its brightness minimum. In the blue part of the spectrum, features from a star of an earlier spectral class are superimposed on the spectrum of a cool giant, so that a variable excess emission is observed at wavelengths of 4000–4200 Å. As opposed to the monotonically decreasing intensity of the Balmer lines (EWHα > EWHβ > EWHγ > EWHδ) in normal stars belonging to the earlier spectral classes, a reverse relationship, with EWHγ < EWHδ is detected in Y Ori. Translated from Astrofizika, Vol. 51, No. 4, pp. 567–575 (November 2008).     

Polarimetric and photometric observations of long-period variables

Observations of 35 long-period variables have been done mainly at the Byurakan Astrophysical Observatory during the last years. A polarimetric monitoring of 34 stars has been carried out with simultaneous photometric measurements for some of them. Photometric data in the UBVR bands have been obtained for the star Y Ori, which is the faintest one. The results show that the degree of light polarization is correlated with the period and brightness of these stars. This indicates that the degree of light polarization is connected with the mass loss as well. Finally the photoelectric observations of the stars Y Ori, T Cep, R Gem, and R Boo show a short-term increase of their brightness in the decreasing branch of their light curves. The measured (U-B) or (B-V) colors of detected rapid variations are bluer than the colors of the star measured before these events. It is supposed that the change of polarization with time, the relatively blue colors of miras near their minimum brightness, and the colors of detected rapid variations may be explained by the influence of a invisible blue companion, as in the case of the star R Aqr. Published in Astrofizika, Vol. 42, No. 3, pp. 341–350, July–September, 1999.     

Radio observations of small Hii regions with identified exciting stars

The radio maps of ten small Hii regions at λλ=2.8, 6 and 11 cm, obtained with the 100-m MPIR radiotelescope, are given. A comparison of the radio fluxes obtained with parameters of exciting stars is carried out. For four compact Hii regions — namely, S146, S152, S237 and S297 — we present the results of observations with the radiotelescope of the U.S.S.R. Academy of Sciences, RATAN-600. The paper also presents estimates of the physical conditions in nebulae, and conclusions are drawn about the possible stage of their evolution.     

The photometric observations of ER vulpeculae: photometric analysis with the W-D code

The photometric observations of ER Vul were obtained in UBV light in 1994, at Birouni Observatory, University of Shiraz, Iran. The three light curves, which are almost complete, have been analyzed separately by means of Wilson and Devinney method (1971). The light curves include proximity effects, wave-like distortions, mutual eclipses, and short term light fluctuations. The appropriate value of the mass ratio of this system was found after extensive searches. ER Vul has a detached configuration where the two components are very nearly fill their Roche lobe. ER Vul has the characteristic of a RS CVn type system. The absolute dimensions for the primary and secondary of this system were calculated from its spectral types and by combining the photometric solution with inferred component radial velocities (Northcott and Bakos, 1967).     

Evaporation and condensation of corundum and silicon carbide grains around the supernova SN1987A in the large magellanic cloud

We investigate the evaporation and condensation of corundum and silicon carbide grains around the supernova SN1987A. We predict the time after outburst of the interaction of the condensed dust with pre-existing dust, with a view to undertaking observations with future instrumentation such as the Infra-Red Space Observatory.     

IRAC photometric analysis and the mid-IR photometric properties of Lyman-break galaxies

We present photometric analysis of deep mid-infrared (mid-IR) observations obtained by Spitzer /IRAC covering the fields Q1422+2309, Q2233+1341, DSF2237a,b, HDFN, SSA22a,b and B20902+34, giving the number counts and the depths for each field. In a sample of 751 Lyman-break galaxies (LBGs) lying in those fields, 443, 448, 137 and 152 are identified at 3.6-, 4.5-, 5.8-, 8.0-μm IRAC bands, respectively, expanding their spectral energy distribution to rest-near-IR and revealing that LBGs display a variety of colours. Their rest-near-IR properties are rather inhomogeneous, ranging from those that are bright in IRAC bands and exhibit  [ R ]−[3.6] > 1.5  colours to those that are faint or not detected at all in IRAC bands with  [ R ]−[3.6] < 1.5  colours and these two groups of LBGs are investigated. We compare the mid-IR colours of the LBGs with the colours of star-forming galaxies and we find that LBGs have colours consistent with star-forming galaxies at   z ∼ 3  . The properties of the LBGs detected in the 8-μm IRAC band (rest-frame K band) are examined separately, showing that they exhibit redder  [ R ]−[3.6]  colours than the rest of the population and that although in general, a multiwavelength study is needed to reach more secure results, IRAC 8-μm band can be used as a diagnostic tool, to separate high z , luminous AGN-dominated objects from normal star-forming galaxies at   z ∼ 3  .     

The age determination of young clusters in the large magellanic cloud by means of integrated photometry

The relationt=t(Q), obtained from theoretical integrated colours (B-V)₀ and (U-B)₀ for Pop. I clusters, has been employed to date a group of 13 young clusters in the LMC. The comparison with the ages derived by the t.o.p. method shows that the theoretical integrated colour indices of clusters, with evolved stars in the mass range 5–15M , are systematically bluer than the observed ones.The analysis performed indicate that, in order to reconcile observed and computed colours, the maximum effective temperature of evolved stars should be suitably lowered. The hypothesis has been advanced that such changes can be obtained by the inclusion of the mass loss in the computation of evolutionary tracks.