Southern African Large Telescope Foundation

Cape Town, South Africa

Southern African Large Telescope Foundation

Cape Town, South Africa
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Miszalski B.,South African Astronomical Observatory | Miszalski B.,Southern African Large Telescope Foundation | Boffin H.M.J.,European Southern Observatory | Corradi R.L.M.,Institute of Astrophysics of Canarias | Corradi R.L.M.,University of La Laguna
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2013

The formation of collimated outflows or jets in planetary nebulae (PNe) is not well understood. There is no evidence for active accretion discs in PNe, making it difficult to decide which of the several proposed jet formation scenarios may be correct. A handful of wide binary central stars of PNe are known to have accreted carbon and slow neutron capture (s-process) enhanced material, the immediate progenitors of barium stars; however, no close binary analogues are known to have passed through a common-envelope (CE) phase. Here we present spectroscopy of the Necklace taken near light-curve minimum that for the first time reveals a carbon-rich (C/O > 1) companion, a carbon dwarf, in a post-CE central star. As unevolved stars do not produce carbon, the chemical enhancement of the secondary can only be explained by accretion from the primary. Accretion most likely happened prior to the CE phase via wind accretion as not enough material can be accreted during the short CE phase. The pair of jets in the Necklace, which are observed to be older than the PN, are therefore likely to have been launched from an accretion disc around the companion during this early accretion phase. This discovery adds significant weight to the emerging scenario that jets in post-CE PNe are primarily launched by an accretion disc around a main-sequence companion before the CE phase. © 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Gvaramadze V.V.,Moscow State University | Kniazev A.Y.,University of Cape Town | Kniazev A.Y.,Southern African Large Telescope Foundation | Chene A.-N.,University of Chile | And 2 more authors.
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2013

We report the discovery of a bow-shock-producing star in the vicinity of the young massive star cluster NGC 3603 using archival data of the Spitzer Space Telescope. Follow-up optical spectroscopy of this star with Gemini-South led to its classification as O6 V. The orientation of the bow shock and the distance to the star (based on its spectral type) suggest that the star was expelled from the cluster, while the young age of the cluster (̃2 Myr) implies that the ejection was caused by a dynamical few-body encounter in the cluster's core. The relative position on the sky of the O6 V star and a recently discovered O2 If*/WN6 star (located on the opposite side of NGC 3603) allows us to propose that both objects were ejected from the cluster via the same dynamical event - a three-body encounter between a single (O6 V) star and a massive binary (now the O2 If*/WN6 star). If our proposal is correct, then one can 'weigh' the O2 If*/WN6 star using the conservation of the linear momentum. Given a mass of the O6 V star of ̃30 Mȯ, we found that at the moment of ejection the mass of the O2 If*/WN6 star was ̃175 Mȯ. Moreover, the observed X-ray luminosity of the O2 If*/WN6 star (typical of a single star) suggests that the components of this originally binary system have merged (e.g., because of encounter hardening). © 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Burgemeister S.,University of Potsdam | Gvaramadze V.V.,Moscow State University | Stringfellow G.S.,University of Colorado at Boulder | Kniazev A.Y.,University of Cape Town | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

Two optically obscured Wolf-Rayet (WR) stars have been recently discovered by means of their infrared (IR) circumstellar shells, which show signatures of interaction with each other. Following the systematics of the WR star catalogues, these stars obtain the names WR 120bb and WR 120bc. In this paper, we present and analyse new near-IR, J-, H- and K-band spectra using the PotsdamWolf-Rayet model atmosphere code. For that purpose, the atomic data base of the code has been extended in order to include all significant lines in the near-IR bands. The spectra of both stars are classified as WN9h. As their spectra are very similar the parameters that we obtained by the spectral analyses hardly differ. Despite their late spectral subtype, we found relatively high stellar temperatures of 63 kK. The wind composition is dominated by helium, while hydrogen is depleted to 25 per cent by mass. Because of their location in the Scutum-Centaurus Arm, WR 120bb and WR 120bc appear highly reddened, AKs ≈ 2 mag. We adopt a common distance of 5.8 kpc to both stars, which complies with the typical absolute K-band magnitude for the WN9h subtype of -6.5 mag, is consistent with their observed extinction based on comparison with other massive stars in the region, and allows for the possibility that their shells are interacting with each other. This leads to luminosities of log(L/L⊙) = 5.66 and 5.54 forWR 120bb and WR 120bc, with large uncertainties due to the adopted distance. The values of the luminosities of WR 120bb and WR 120bc imply that the immediate precursors of both stars were red supergiants (RSG). This implies in turn that the circumstellar shells associated with WR 120bb and WR 120bc were formed by interaction between theWR wind and the dense material shed during the preceding RSG phase. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


Brosch N.,Tel Aviv University | Kniazev A.Y.,South African Astronomical Observatory | Kniazev A.Y.,Southern African Large Telescope Foundation | Moiseev A.,Circassia | Pustilnik S.A.,Circassia
Monthly Notices of the Royal Astronomical Society | Year: 2010

We show that an object classified as a galaxy in on-line data bases and revealed on sky survey images as a distant ring galaxy is a rare case of polar ring galaxy (PRG) where the ring is only slightly inclined to the equatorial plane of the central body (CB). Imaging information from the Sloan Digital Sky Survey (SDSS) indicates that the diameter of the ring is about 36 kpc. The SDSS data was combined with long-slit spectroscopic observations and with Fabry-Pérot interferometer Hβ mapping obtained at the Russian Academy of Sciences 6-m telescope. We derived the complex morphologies of this presumed ring galaxy from a combination of SDSS images and from the kinematical behaviour of the CB and of the ring, and determined the stellar population compositions of the two components from the SDSS colours, from the spectroscopy and from models of evolutionary stellar synthesis. The metallicity of the ring material is slightly underabundant. The total luminosity and the total mass of the system are not extreme, but the rather high M/L ≃ 20 indicates the presence of large amounts of dark matter. We propose two alternative explanations of the appearance of this object. One is a ring formed by two semicircular and tight spiral arms at the end of a central bar. The apparent inclination between the ring and the CB, and a strange kink at the north-east end of the ring, could be the result of a warp or of precession of the ring material. The object could, therefore, be explained as an extreme SBa(R) galaxy. The other possibility is that we observe a PRG where the inner object is an S0 and the ring is significantly more luminous than the central object. The compound object would then be similar to the NGC 4650A galaxy, but then it would be a rare object, with a polar component only modestly inclined to the equatorial plane of the CB. Arguments for (and against) both explanations are given and discussed, with the second alternative being more acceptable. © 2009 RAS.


Moiseev A.V.,Circassia | Pustilnik S.A.,Circassia | Kniazev A.Y.,South African Astronomical Observatory | Kniazev A.Y.,Southern African Large Telescope Foundation
Monthly Notices of the Royal Astronomical Society | Year: 2010

The study of ionized gas morphology and kinematics in nine extremely metal-deficient (XMD) galaxies with the scanning Fabry-Perot interferometer on the Special Astrophysical Observatory (SAO) 6-m telescope is presented. Some of these very rare objects (with currently known range of O/H of 7.12 < 12 + log(O/H) < 7.65, or ) are believed to be the best proxies of 'young' low-mass galaxies in the high-redshift Universe. One of the main goals of this study is to look for possible evidence of star formation (SF) activity induced by external perturbations. Recent results from H i mapping of a small subsample of XMD star-forming galaxies provided confident evidence for the important role of interaction-induced SF. Our observations provide complementary or new information that the great majority of the studied XMD dwarfs have strongly disturbed gas morphology and kinematics or the presence of detached components. We approximate the observed velocity fields by simple models of a rotating tilted thin disc, which allows us the robust detection of non-circular gas motions. These data, in turn, indicate the important role of current/recent interactions and mergers in the observed enhanced SF. As a by-product of our observations, we obtained data for two Low Surface Brightness (LSB) dwarf galaxies: Anon J012544+075957 that is a companion of the merger system UGC 993, and SAO 0822+3545 which shows off-centre, asymmetric, low star formation rate star-forming regions, likely induced by the interaction with the companion XMD dwarf HS 0822+3542. © 2010 The Authors. Journal compilation © 2010 RAS.


Pustilnik S.A.,Circassia | Martin J.-M.,University of Paris Descartes | Tepliakova A.L.,Circassia | Kniazev A.Y.,South African Astronomical Observatory | Kniazev A.Y.,Southern African Large Telescope Foundation
Monthly Notices of the Royal Astronomical Society | Year: 2011

We present the results of a complex study of the low surface brightness dwarf (LSBD) gas-rich galaxies J0723+3621, J0737+4724 and J0852+1350, which reside in the nearby Lynx-Cancer void. Their ratios M(Hi)/LB, according to Hi data obtained with the Nançay Radio Telescope (NRT), are respectively ~3.9, ~2 and ~2.6. For the two latter galaxies, we derived an oxygen abundance corresponding to the value of 12+log(O/H) 7.3, using spectra from the Russian 6-m telescope (BTA) and the Sloan Digital Sky Survey (SDSS) data base. We found two additional blue LSBDs, J0723+3622 and J0852+1351, which appear to be physical companions of J0723+3621 and J0852+1350 situated at projected distances of ~12-13kpc. The companion relative velocities, derived from the BTA spectra, are ΔV=+89kms-1 and +30kms-1 respectively. The geometry and relative orientation of orbits and spins in these pairs indicate, respectively, prograde and polar encounters for J0723+3621 and J0852+1350. The NRT Hi profiles of J0723+3621 and J0723+3622 indicate a sizeable gas flow in this system. The SDSS u, g, r, i images of the five dwarfs are used to derive photometric parameters and exponential or Sersic disc model fits. For three of them, the (u-g), (g-r), (r-i) colours of the outer parts, when compared with PEGASE evolutionary tracks, provide evidence for the dominance of old stellar populations with ages of T~ (8-10) ± 3 Gyr. For J0723+3622 and J0737+4724 the outer region colours appear rather blue, implying ages of the oldest visible stars of Gyr. The new LSB galaxies complement the list of known most metal-poor and 'unevolved' dwarfs in this void, including DDO68, SDSSJ0812+4836, SDSSJ0926+3343 and SAO0822+3545. This unique concentration of 'unevolved' dwarf galaxies in a small cell of the nearby Universe implies a physical relationship between slow galaxy evolution and a void-type global environment. We also compare the baryonic content of these LSBDs with predictions from the most updated cosmological simulations. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.


Miszalski B.,South African Astronomical Observatory | Miszalski B.,Southern African Large Telescope Foundation | Mikolajewska J.,Nicolaus Copernicus Astronomical Center
Monthly Notices of the Royal Astronomical Society | Year: 2014

We introduce the first results from an ongoing, systematic survey for new symbiotic stars selected from the AAO/UKST SuperCOSMOS Ha Survey. The survey aims to identify and characterize the fainter population of symbiotic stars under-represented in extant catalogues. The accreting white dwarfs (WDs) in symbiotic stars, fuelled by their red giant donors with high mass-loss rate winds, make them promising candidates for Type Ia supernovae. Several candidates were observed spectroscopically with the Southern African Large Telescope. A total of 12 bona fide and 3 possible symbiotic stars were identified. The most remarkable example is a rare carbon-rich symbiotic star that displays coronal [Fe X] λ 6375 emission, suggesting it may be a supersoft X-ray source with a massive WD. Several other emission line objectswith near-infrared colours similar to symbiotic stars are listed in an appendix, including six B[e] stars, four planetary nebulae (PNe), two possible Be stars, one [WC9] Wolf-Rayet (WR) central star of a PN and one WC9WR star. These initial discoveries will help shape and refine the candidate selection criteria that we expect will uncover several more symbiotic stars as the survey progresses. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Miszalski B.,South African Astronomical Observatory | Miszalski B.,Southern African Large Telescope Foundation | MikoLajewska J.,Nicolaus Copernicus Astronomical Center | Udalski A.,University of Warsaw
Monthly Notices of the Royal Astronomical Society | Year: 2013

Symbiotic stars are interacting binaries with the longest orbital periods, and their multicomponent structure makes them rich astrophysical laboratories. The accretion of a high-mass-lossratered giant wind on to a white dwarf (WD) makes them promising Type Ia supernova (SN Ia) progenitor.Systematic surveys for new Galactic symbiotic stars are critical to identify new promising SN Iaprogenitors (e.g. RS Oph) and to better estimate the total population size to compare against SN Ia rates. Central to the latter objective is building a complete census of symbiotic stars towards the Galactic bulge. Here we report on the results of a systematic survey of Hα emission-line stars covering 35 deg2. It is distinguished by the combination of deep optical spectroscopy and long-termlight curves that improve the certainty of our classifications. A total of 20 bona fide symbiotic stars are found (13 S-types, 6 D-types and 1 D'-type), 35 per cent of which show the symbiotic specific Raman-scattered OVI emission bands, as well as 15 possible symbiotic stars that require further study (six S-types and nine D-types). Light curves show a diverse range of variability including stellar pulsations (semi-regular and Mira), orbital variations and slow changes due to dust. Orbital periods are determined for five S-types and Mira pulsation periods for three D-types. The most significant D-type found is H1-45 and its carbon Mira with a pulsation period of 408.6 d, corresponding to an estimated period-luminosity relation distance of ̃6.2 ± 1.4 kpc and MK = -8.06 ± 0.12 mag. If H1-45 belongs to the Galactic bulge, then it would be the first bona fide luminous carbon star to be identified in the Galactic bulge population. The lack of luminous carbon stars in the bulge is a longstanding unsolved problem. A possible explanation for H1-45 may be that the carbon enhancement was accreted from the progenitor of the WD companion. A wide variety of unusual emission-line stars were also identified. These include central stars of planetary nebulae (PNe) [one(WC10-11) Wolf-Rayet and five with high-density cores], two novae, two WN6 Wolf-Rayet stars, two possible Be stars, a B[e] star with a bipolar outflow, an ultracompact HII region and a dMe flare star. Dust obscuration events were found in two central stars of PNe, increasing the known cases tofive, as well as one WN6 star. There is considerable scope to uncover several more symbiotic starstowards the bulge, many of which are currently misclassified as PNe, provided that deep spectroscopy is combined with optical and near-infrared light curves. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Gvaramadze V.V.,Moscow State University | Kniazev A.Y.,South African Astronomical Observatory | Kniazev A.Y.,Southern African Large Telescope Foundation | Fabrika S.,Special Astrophysical Observatory
Monthly Notices of the Royal Astronomical Society | Year: 2010

Massive evolved stars lose a large fraction of their mass via copious stellar wind or instant outbursts. During certain evolutionary phases, they can be identified by the presence of their circumstellar nebulae. In this paper, we present the results of a search for compact nebulae (reminiscent of circumstellar nebulae around evolved massive stars) using archival 24-μm data obtained with the Multiband Imaging Photometer for Spitzer. We have discovered 115 nebulae, most of which bear a striking resemblance to the circumstellar nebulae associated with luminous blue variables (LBVs) and late WN-type (WNL) Wolf-Rayet (WR) stars in the Milky Way and the Large Magellanic Cloud (LMC). We interpret this similarity as an indication that the central stars of detected nebulae are either LBVs or related evolved massive stars. Our interpretation is supported by follow-up spectroscopy of two dozen of these central stars, most of which turn out to be either candidate LBVs (cLBVs), blue supergiants or WNL stars. We expect that the forthcoming spectroscopy of the remaining objects from our list, accompanied by the spectrophotometric monitoring of the already discovered cLBVs, will further increase the known population of Galactic LBVs. This, in turn, will have profound consequences for better understanding the LBV phenomenon and its role in the transition between hydrogen-burning O stars and helium-burning WR stars. We also report on the detection of an arc-like structure attached to the cLBV HD 326823 and an arc associated with the LBV R99 (HD 269445) in the LMC. © 2010 The Authors. Journal compilation © 2010 RAS.


Miszalski B.,South African Astronomical Observatory | Miszalski B.,Southern African Large Telescope Foundation | Mikolajewska J.,Nicolaus Copernicus Astronomical Center | Udalski A.,University of Warsaw
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2014

We report on the discovery of a newSmall MagellanicCloud symbiotic star, OGLE-SMC-LPV- 00861, previously catalogued as Hα emission line source LIN 9. The OGLE light curve shows multiple-maxima outburst behaviour over ~1200 dwith amaximum outburst of ΔV=1.5mag. An optical spectrum of LIN 9 taken with the Southern African Large Telescope at quiescence reveals a K5 red giant with emission lines confirming its symbiotic star nature, demonstrating the potential use of ongoing large time-domain surveys to identify strong symbiotic star candidates. It is the first Magellanic symbiotic star proven to show poorly understood Z And outbursts. At outburst the estimated hot component luminosity is L ~ 3165 L⊙, compared to L ~ 225 L⊙ at quiescence. Further observations are needed, especially at outburst, to better understand this unique Z And-like system at a known distance, and to provide essential input to physical models of the Z And phenomenon. © 2014 The Authors.

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