Home About us Contact
|
Home About us Contact | ||
|
|
||
Small Magellanic Cloud (small + magellanic_cloud)
Selected AbstractsHigh-dispersion spectroscopy of two A supergiant systems in the Small Magellanic Cloud with novel propertiesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2010R. E. Mennickent ABSTRACT We present the results of a spectroscopic investigation of two novel variable bright blue stars in the SMC, OGLE004336.91-732637.7 (SMC-SC3) and the periodically occulted star OGLE004633.76-731204.3 (SMC-SC4), whose photometric properties were reported by Mennickent et al. (2010). High-resolution spectra in the optical and far-UV show that both objects are actually A + B type binaries. Three spectra of SMC-SC4 show radial velocity variations, consistent with the photometric period of 184.26 d found in Mennickent et al. 2010. The optical spectra of the metallic lines in both systems show combined absorption and emission components that imply that they are formed in a flattened envelope. A comparison of the radial velocity variations in SMC-SC4 and the separation of the V and R emission components in the H, emission profile indicate that this envelope, and probably also the envelope around SMC-SC3, is a circumbinary disc with a characteristic orbital radius some three times the radius of the binary system. The optical spectra of SMC-SC3 and SMC-SC4 show, respectively, He i emission lines and discrete blue absorption components (BACs) in metallic lines. The high excitations of the He i lines in the SMC-SC3 spectrum and the complicated variations of Fe ii emission and absorption components with orbital phase in the spectrum of SMC-SC4 suggests that shocks occur between the winds and various static regions of the stars' corotating binary-disc complexes. We suggest that BACs arise from wind shocks from the A star impacting the circumbinary disc and a stream of former wind-efflux from the B star accreting on to the A star. The latter picture is broadly similar to mass transfer occurring in the more evolved (but less massive) algol (B/A + K) systems, except that we envision transfer occurring in the other direction and not through the inner Lagrangian point. Accordingly, we dub these objects prototype of a small group of Magellanic Cloud wind-interacting A + B binaries. [source] Be/X-ray binary SXP6.85 undergoes large Type II outburst in the Small Magellanic CloudMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2010L. J. Townsend ABSTRACT The Small Magellanic Cloud (SMC) Be/X-ray binary pulsar SXP6.85 = XTE J0103,728 underwent a large Type II outburst beginning on 2008 August 10. The source was consistently seen for the following 20 weeks (MJD = 54688,54830). We present X-ray timing and spectroscopic analysis of the source as a part of our ongoing Rossi X-ray Timing Explorer (RXTE) monitoring campaign and INTEGRAL key programme monitoring the SMC and 47 Tuc. A comparison with the Optical Gravitational Lensing Experiment (OGLE) III light curve of the Be counterpart shows the X-ray outbursts from this source coincide with times of optical maximum. We attribute this to the circumstellar disc increasing in size, causing mass accretion on to the neutron star. Ground based infrared photometry and H, spectroscopy obtained during the outburst are used as a measure of the size of the circumstellar disc and lend support to this picture. In addition, folded RXTE light curves seem to indicate complex changes in the geometry of the accretion regions on the surface of the neutron star, which may be indicative of an inhomogeneous density distribution in the circumstellar material causing a variable accretion rate on to the neutron star. Finally, the assumed inclination of the system and H, equivalent width measurements are used to make a simplistic estimate of the size of the circumstellar disc. [source] Seven young star clusters in the inner region of the Small Magellanic CloudMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008Andrés E. Piatti ABSTRACT We present CCD photometry in the Washington system C and T1 passbands down to T1, 22 in the fields of L35, L45, L49, L50, L62, L63 and L85, seven poorly studied star clusters in the inner region of the Small Magellanic Cloud (SMC). We measured T1 magnitudes and C,T1 colours for a total of 114 826 stars distributed throughout cluster areas of 13.7 × 13.7 arcmin2 each. Cluster radii were estimated from star counts distributed throughout the entire observed fields. The seven clusters are generally characterized by a relatively small angular size and by a high field star contamination. We performed an in-depth analysis of the field star contamination of the colour,magnitude diagrams (CMDs), and statistically cleaned the cluster CMDs. Based on the best fits of isochrones computed by the Padova group to the (T1, C,T1) CMDs, we derive ages for the sample, assuming Z= 0.004, finding ages between 25 Myr and 1.2 Gyr. We then examined different relationships between positions in the SMC, age and metallicity of a larger sample of clusters including our previous work whose ages and metallicities are on the same scale used in this paper. We confirm previous results in the sense that the further a cluster is from the centre of the galaxy, the older and more metal poor it is, with some dispersion; although clusters associated with the Magellanic Bridge clearly do not obey the general trend. The number of clusters within , 2° of the SMC centre appears to have increased substantially after ,2.5 Gyr ago, hinting at a burst. [source] An ATCA radio-continuum study of the Small Magellanic Cloud , IV.MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006A multifrequency analysis of the N 66 region ABSTRACT Traditional identification of supernova remnants (SNRs) include the use of radio spectral index, optical spectral studies (including strong [S ii], [N ii], [O i], [O ii] and [O iii] lines) and X-ray co-identifications. Each of these can have significant limitations within the context of a particular SNR candidate and new identification methods are continually sought. In this paper, we explore subtraction techniques by Ye, Turtle and Kennicutt to remove thermal emission estimated from H, flux from radio-continuum images. The remaining non-thermal emission allows the identification of SNRs embedded within these H ii regions. Subtraction images of the N 66 region in the Small Magellanic Cloud (SMC) using H, wide-field optical CCD images from the Curtis Schmidt Telescope and the recent Australia Telescope Compact Array (ATCA)/Parkes radio-continuum (1420, 2370, 4800 and 8640 MHz) data are presented as an example. These show three SNRs (B0057 , 724, B0056 , 724 and B0056 , 725) separated from their surrounding H ii radio emission. 2.3-m dual-beam spectrograph long-slit spectra from selected regions within N 66 suggest the presence of an additional SNR with no radio or X-ray emission. Radio spectral index, [S ii]/H, ratio and archived Chandra images of N 66 combine to give a more coherent picture of this region, confirming B0057 , 724 as an SNR. The N 66 nebula complex is divided into 10 components, composed separately of these SNRs and H ii regions. [source] OGLE observations of four X-ray binary pulsars in the Small Magellanic CloudMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2000M. J. Coe This paper presents analysis and interpretation of OGLE photometric data of four X-ray binary pulsar systems in the Small Magellanic Cloud (SMC): 1WGA J0054.9-7226, RX J0050.7-7316, RX J0049.1-7250 and 1SAX J0103.2-7209. In each case, the probable optical counterpart is identified on the basis of its optical colours. In the case of RX J0050.7-7316 the regular modulation of its optical light curve appears to reveal an ellipsoidal modulation with a period of 1.416 d. Using reasonable masses for the neutron star and the B star, we show that the amplitude and relative depths of the minima of the I -band light curve of RX J0050.7-7316 can be matched with an ellipsoidal model where the B star nearly fills its Roche lobe. For mass ratios in the range of 0.12 to 0.20, the corresponding best-fitting inclinations are about 55° or larger. The neutron star would be eclipsed by the B star at inclinations larger than ,60° for this particular mass ratio range. Thus RX J0050.7-7316 is a good candidate system for further study. In particular, we would need additional photometry in several colours, and most importantly, radial velocity data for the B star before we could draw more quantitative conclusions about the component masses. [source] Integrated spectroscopic study of 7 star clusters in the Small Magellanic CloudASTRONOMISCHE NACHRICHTEN, Issue 3 2010M.L. Talavera Abstract We present flux-calibrated integrated spectra for 7 star clusters belonging to the Small Magellanic Cloud in the optical range (,3600,7000 Ä), obtained at CASLEO (Argentina). Three out of the 7 clusters were not previously studied so their ages and reddening values are determined for the first time in the current study. Using the equivalent widths of selected spectroscopic lines and comparing the cluster spectra with template spectra of known properties, we derive foreground interstellar reddening and age. The clusters are in the (5,300) Myr age range and their E (B , V) colour excesses were in all cases smaller than 0.12. The present data also contribute to enlarge the cluster spectral library at the metallicity level of the Small Magellanic Cloud. The buildup of such database, which also includes Galactic and Large Magellanic Cloud clusters, is a long-term project that we have been developing and which has proved to be useful in the analysis of stellar populations of extragalactic systems (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Dust mass-loss rates from asymptotic giant branch stars in the Fornax and Sagittarius dwarf spheroidal galaxiesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008Eric Lagadec ABSTRACT To study the effect of metallicity on the mass-loss rate of asymptotic giant branch (AGB) stars, we have conducted mid-infrared photometric measurements of such stars in the Sagittarius and Fornax dwarf spheroidal galaxies with the 10-,m camera VISIR at the Very Large Telescope. We derive mass-loss rates for 29 AGB stars in Sgr dSph and two in Fornax. The dust mass-loss rates are estimated from the K,[9] and K,[11] colours. Radiative transfer models are used to check the consistency of the method. Published IRAS and Spitzer data confirm that the same tight correlation between K,[12] colour and dust mass-loss rates is observed for AGB stars from galaxies with different metallicities, i.e., the Galaxy, the Large Magellanic Clouds and the Small Magellanic Clouds. The derived dust mass-loss rates are in the range 5 × 10,10 to 3 × 10,8 M, yr,1 for the observed AGB stars in Sgr dSph and around 5 × 10,9 M, yr,1 for those in Fornax; while values obtained with the two different methods are of the same order of magnitude. The mass-loss rates for these stars are higher than the nuclear burning rates, so they will terminate their AGB phase by the depletion of their stellar mantles before their core can grow significantly. Some observed stars have lower mass-loss rates than the minimum value predicted by theoretical models. [source] Mira variables in the Galactic bulge with OGLE-II dataMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2005Noriyuki Matsunaga ABSTRACT We have extracted a total of 1968 Mira variables from the Optical Gravitational Lensing Experiment II (OGLE-II) data base in the Galactic bulge region. Among them, 1960 are associated with 2 Micron All-sky Survey (2MASS) sources, and 1541 are further identified with Midcourse Space Exploration (MSX) point sources. Their photometric properties are compared with those of Mira variables in the Large and Small Magellanic Clouds. We have found that mass-losing stars with circumstellar matter are reddened such that the colour dependence of the absorption coefficient is similar to that of interstellar matter. We also discuss the structure of the bulge. The surface number density of the bulge Mira variables is well correlated with the 2.2-,m surface brightness obtained by the Cosmic Background Explorer (COBE) satellite. Using this relation, the total number of Mira variables in the bulge is estimated to be about 6 × 105. The log P,K relation of the Mira variables gives their space distribution which supports the well-known asymmetry of the bar-like bulge. [source] Radial velocities, dynamics of stars and nebulosities with GAIA and VLT-GIRAFFEASTRONOMISCHE NACHRICHTEN, Issue 9-10 2008C. Martayan Abstract This document is divided in two parts. The first part deals with the radial velocities (RV) distributions for B-type stars and nebulosities observed with the VLT-GIRAFFE in the Large and Small Magellanic Clouds towards the open clusters NGC2004 and NGC330. Thanks to the resolution of GIRAFFE spectra, we found that the RV distribution for the nebulosities in the LMC is bi-modal. This bi-modality can be interpreted, in term of dynamics, by the expansion of the LMC4 super-bubble. The second part deals with the GAIA space mission and the determination of the radial velocities by using Radial Velocity Spectrometer (RVS) spectra. The methods to determine the radial velocities are presented as well as preliminary results on simulated RVS spectra. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||