A. Y. Kniazev

Revealing evolved massive stars with Spitzer

Massive evolved stars loss a large fraction of their mass via copious stellar wind or instant outbursts and during certain evolutionary phases they can b e identified via the presence of their circumstellar nebulae. In this paper, we present the r esults of search for compact nebulae (reminiscent of circumstellar nebulae around evolved m assive stars) using archival 24 μm data obtained with the Multiband Imaging Photometer for Spitzer. We discovered 115 nebulae, most of which bear a striking resemblance to the circums tellar nebulae associated with Luminous Blue Variables (LBVs) and late WN-type (WNL) WolfRayet (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 LB Vs or related evolved massive stars. Our interpretation is supported by follow-up spectroscopy f two dozens of these central stars, most of which turns out to be either candidate LBVs (cLBVs), b lue supergiants or WNL stars. We expect that the forthcoming spectroscopy of the remainin g objects from our list, accompanied by the spectrophotometric monitoring of the already discovered cLBVs, will further increase the known population of Galactic LBVs, which in tur n would 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 rep rt the detection of an arc-like structure attached to the cLBV HD 326823 and an arc a ssociated with the LBV R99 (HD 269445) in the LMC.

THE ABUNDANCE PROPERTIES OF NEARBY LATE-TYPE GALAXIES. I. THE DATA

We investigate the oxygen and nitrogen abundance distributions across the optical disks of 130 nearby late-type galaxies using around 3740 published spectra of H II regions. We use these data in order to provide homogeneous abundance determinations for all objects in the sample, including H II regions in which not all of the usual diagnostic lines were measured. Examining the relation between N and O abundances in these galaxies we find that the abundances in their centers and at their isophotal R {sub 25} disk radii follow the same relation. The variation in N/H at a given O/H is around 0.3 dex. We suggest that the observed spread in N/H may be partly caused by the time delay between N and O enrichment and the different star formation histories in galaxies of different morphological types and dimensions. We study the correlations between the abundance properties (central O and N abundances, radial O and N gradients) of a galaxy and its morphological type and dimension.

Adaptive optics imaging and optical spectroscopy of a multiple merger in a luminous infrared galaxy

We present near-infrared (NIR) adaptive optics imaging obtained with VLT/NACO and optical spectroscopy from the Southern African Large Telescope of a luminous IR galaxy (LIRG) IRAS 19115-2124. Thes ...

Characterization of the nearby L/T Binary Brown Dwarf WISE J104915.57–531906.1 at 2 Pc from the Sun

WISE J104915.57–531906.1 is a L/T brown dwarf binary located 2 pc from the Sun. The pair contains the closest known brown dwarfs and is the third closest known system, stellar or sub-stellar. We report comprehensive follow-up observations of this newly uncovered system. We have determined the spectral types of both components (L8 ± 1, for the primary, agreeing with the discovery paper; T1.5 ± 2 for the secondary, which was lacking spectroscopic type determination in the discovery paper) and, for the first time, their radial velocities (V_(rad) ~ 23.1, 19.5 km s^(–1)) using optical spectra obtained at the Southern African Large Telescope and other facilities located at the South African Astronomical Observatory (SAAO). The relative radial velocity of the two components is smaller than the range of orbital velocities for theoretically predicted masses, implying that they form a gravitationally bound system. We report resolved near-infrared JHK_S photometry from the Infrared Survey Facility telescope at the SAAO which yields colors consistent with the spectroscopically derived spectral types. The available kinematic and photometric information excludes the possibility that the object belongs to any of the known nearby young moving groups or associations. Simultaneous optical polarimetry observations taken at the SAAO 1.9 m give a non-detection with an upper limit of 0.07%. For the given spectral types and absolute magnitudes, 1 Gyr theoretical models predict masses of 0.04-0.05 M _☉ for the primary, and 0.03-0.05 M _☉ for the secondary.

Photometry of 2006 RH120: an asteroid temporary captured into a geocentric orbit

Aims. From July 2006 to July 2007 a very small asteroid orbited the Earth within its Hill sphere. We used this opportunity to study its rotation and estimate its diameter and shape. Methods. Due to its faintness, 2006 RH120 was observed photometrically with the new 10-m SALT telescope at the SAAO (South Africa). We obtained data on four nights: 11, 15, 16, and 17 March 2007 when the solar phase angle remained almost constant at 74 ◦ . The observations lasted about an hour each night and the object was exposed for 7−10 s through the “clear” filter. Results. From the lightcurves obtained on three nights we derived two solutions for a synodical period of rotation: P1 = 1.375 ± 0.001 min and P2 = 2.750 ± 0.002 min. The available data are not sufficient to choose between them. The absolute magnitude of the object was found to be H = 29.9 ± 0.3 mag (with the assumed slope parameter G = 0.25) and its effective diameter D = 2− 7m , depending on the geometric albedo pV (with the most typical near-Earth asteroids albedo pV = 0.18 its diameter would be D = 3.3 ± 0.4 m). The body has an elongated shape with the a/b ratio greater than 1.4. It probably originates in low-eccentricity Amor or Apollo orbits. There is still a possibility, which needs further investigation, that it is a typical near-Earth asteroid that survived the aerobraking in the Earth’s atmosphere and returned to a heliocentric orbit similar to that of the Earth.

RR Lyrae variables: visual and infrared luminosities, intrinsic colours and kinematics

We use UCAC4 proper motions and WISE W1-band apparent magnitudes intensity-mean for almost 400 field RR Lyrae variables to determine the parameters of the velocity distribution of Galactic RR Lyrae population and constrain the zero points of the metallicity- relation and those of the period-metallicity- -band and period-metallicity- -band luminosity relations via statistical parallax. We find the mean velocities of the halo- and thick-disc RR Lyrae populations in the solar neighbourhood to be (U0(Halo), V0(Halo), W0(Halo)) = (-7 +/- 9, -214 +/- 10, -10 +/- 6) km/s and (U0(Disc), V0(Disc), W0(Disc)) =(-13 +/- 7, -37 +/- 6, -17 +/- 4) km/s, respectively, and the corresponding components of the velocity-dispersion ellipsoids, (sigma VR(Halo), sigma Vphi(Halo), sigma Vtheta(Halo)) = (153 +/- 9, 101 +/- 6, 96 +/- 5) km/s and (sigma VR(Disc), sigma Vphi(Disc), sigma Vtheta(Disc)) = (46 +/- 7, 37 +/- 5, 27 +/- 4) km/s, respectively. The fraction of thick-disc stars is estimated at 0.22 +/- 0.03. The corrected IR period-metallicity-luminosity relations are = -0.769 +0.088 [Fe/H]- 2.33 mathoprm log PF and = -0.825 + 0.088 [Fe/H] -2.33 mathoprm log PF, and the optical metallicity-luminosity relation, [Fe/H]- , is = +1.094 + 0.232 [Fe/H], with a standard error of +/- 0.089, implying an LMC distance modulus of 18.32 +/- 0.09, a solar Galactocentric distance of 7.73 +/- 0.36 kpc, and the M31 and M33 distance moduli of DM(M31) = 24.24 +/- 0.09 (D = 705 +/- 30 kpc) and DM(M33) = 24.36 +/- 0.09 (D = 745 +/- 31 kpc), respectively. Extragalactic distances calibrated with our RR Lyrae star luminosity scale imply a Hubble constant of ~80 km/s/Mpc. Our results suggest marginal prograde rotation for the population of halo RR Lyraes in the Milky Way.

SDSS J092609.45+334304.1: a nearby unevolved galaxy

We present the results of observations of the very low surface brightness (VLSB) dwarf galaxy SDSS J092609.45+334304.1 with extreme parameters which indicate its unevolved status. Namely, its value of O/H, derived as an average of that in two adjacent H ii regions at the NE edge of the disc, corresponds to the parame- ter 12+log(O/H)=7.12±0.02, which is amongst two lowest known. The total HI flux measurement obtained with the Nancay Radio Telescope and the photometric results imply that the galaxy ratio M(HI)/LB �3.0, is among the top known in the Local Vol- ume. The galaxy is situated in the region of a nearby underdense region known as the Lynx-Cancer void, where other, unevolved galaxies, including DDO 68, HS 0832+3542 and SAO 0822+3545, are known to be present. The total mass of this almost edge-on VLSB galaxy is �8.3 times larger than its baryonic mass, implying the dynamical dominance of Dark Matter (DM) halo. The (u g),(g r) colours of outer parts of this galaxy are consistent with the ages of its main stellar population of 1-3 Gyr. Thanks to the galaxy isolation, the small effect of current or recent star formation (SF), its proximity and rather large HI flux (�2.5 Jy·km s −1 ), this VLSB dwarf is a good laboratory for the detailed study of DM halo properties through HI kinematics and the star formation processes in very metal-poor low surface density environment. This finding, along with the discovery of other unusual dwarf galaxies in this void, provides evidence for the relation between galaxy evolution and its very low-density environment for the baryonic mass range of 10 8 to 10 9 M⊙. This relation seems to be consistent with that expected in theCDM models of galaxy and structure formation.

[O iii] λ5007 AND X-RAY PROPERTIES OF A COMPLETE SAMPLE OF HARD X-RAY SELECTED AGNs IN THE LOCAL UNIVERSE

We study the correlation between the [O III]

IRC -10414: a bow-shock-producing red supergiant star

\lambda 5007

Abell 48 – a rare WN-type central star of a planetary nebula

and X-ray luminosities of local Active Galactic Nuclei (AGNs), using a complete, hard X-ray (