Stray light analysis of the Xinglong 2.16-m telescope

An effort towards understanding the problems associated with stray light related to the Xinglong2.16-m telescope is presented to estimate the stray light performance of the telescope itself and provide a method for improving stray light suppression. Stray light analysis for the 2.16-m telescope model, which consists of an onion shaped dome, telescope structure, equatorial mount and telescope optics, has been developed in two cases(1) pointing to 60?and(2) pointing to zenith, in both azimuth and elevation directions.The Point Source Normalized Irradiance Transmittance(PSNIT), which is generally used for assessing stray light and is uncorrelated to entrance aperture, is calculated with a series of off-axis angles. It shows that the PSNIT values are less than 10~(-7) when off-axis angles are larger than ±20?. The dominant contributors to stray light(primary and secondary mirror, telescope structure and dome) are identified to guide performance improvement. The analyses indicate that significant benefit can be realized by adding only five vanes inside the bottom portion of the secondary baffle. In the case of pointing to zenith, the PSNIT values will decrease about 40% on average.     

Metallicity and star formation activities of the interacting system Arp 86 from observations with MOS on the Xinglong 2.16m telescope

We present an analysis of the metallicity and star formation activities of H II regions in the interacting system Arp 86, based on the first scientific observations using multi-object spectroscopy with the 2.16 m telescope at the Xinglong Observing Station. We find that the oxygen abundance gradient in Arp 86 is flatter than that in normal disk galaxies, which confirms that gas inflows caused by tidal forces during encounters can flatten the metallicity distributions in galaxies. The companion galaxy NGC 7752 is currently experiencing a galaxy-wide starburst with a higher star formation rate surface density than the main galaxy NGC 7753, which can be explained in that the companion galaxy is more susceptible to the effects of interaction than the primary. We also find that the galaxy 2MASX J23470758+2926531 has similar abundance and star formation properties to NGC 7753, and may be a part of the Arp 86 system.     

New age estimates of M31 globular clusters from multicolour photometry

The large majority of extragalactic star cluster studies performed to date essentially use multicolour photometry, combined with theoretical stellar synthesis models, to derive ages, masses, extinction estimates and metallicities. M31 offers a unique laboratory for studies of globular cluster (GC) systems. In this paper, we obtain new age estimates for 91 M31 GCs, based on improved photometric data, updated theoretical stellar synthesis models and sophisticated new fitting methods. In particular, we used photometric measurements from the Two Micron All Sky Survey (2MASS), which, in combination with optical photometry, can partially break the well-known age–metallicity degeneracy operating at ages in excess of a few Gyr. We show robustly that previous age determinations based on photometric data were affected significantly by this age–metallicity degeneracy. Except for one cluster, the ages of our other sample GCs are all older than 1 Gyr. Their age distribution shows populations of young- and intermediate-age GCs, peaking at ∼3 and 8 Gyr, respectively, as well as the 'usual' complement of well-known old GCs, i.e. GCs of similar age as the majority of the Galactic GCs. Our results also show that although there is significant scatter in metallicity at any age, there is a notable lack of young metal-poor and old metal-rich GCs, which might be indicative of an underlying age–metallicity relationship among the M31 GC population.     

A new population of extended, luminous star clusters in the halo of M31

We present three new clusters discovered in the halo of M31 which, although having globular-like colours and luminosities, have unusually large half-light radii, ∼30 pc. They lie at projected galactocentric distances of ≈15 to ≈35 kpc. These objects begin to fill the gap in parameter space between globular clusters and dwarf spheroidals, and are unlike any clusters found in the Milky Way, or elsewhere to date. Colour–magnitude diagrams, integrated photometric properties and derived King profile fit parameters are given, and we discuss possible origins of these clusters and their relationships to other populations.     

The LAMOST spectroscopic survey of globular clusters in M31and M33.I.catalog and new identifications

We present a catalog of 908 objects observed with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST) in fields in the vicinity of M31 and M33, targeted as globular clusters(GCs) and candidates. The targets include known GCs and candidates selected from the literature, as well as new candidates selected from the Sloan Digital Sky Survey(SDSS). Analysis shows that 356 of them are likely GCs with various confidence levels, while the remaining ones turn out to be background galaxies and quasars, stars and H II regions in M31 or foreground Galactic stars. The 356 likely GCs include 298 bona fide GCs and 26 candidates known in the literature. Three candidates, selected from the Revised Bologna Catalog of M31 GCs and candidates(RBC) and one possible cluster from Johnson et al., are confirmed to be bona fide clusters. We search for new GCs in the halo of the M31 among the new candidates selected from the SDSS photometry. Based on radial velocities yielded by LAMOST spectra and visual examination of the SDSS images, we find 28 objects, 5bona fide and 23 likely GCs. Among the five bona fide GCs, three have been recently discovered independently by others, and the remaining 25 are our new identifications,including two bona fide ones. The newly identified objects fall at projected distances ranging from 13 to 265 kpc from M31. Of the two newly discovered bona fide GCs,one is located near M33, probably a GC belonging to M33. The other bona fide GC falls on the Giant Stream with a projected distance of 78 kpc from M31. Of the 23 newly identified likely GCs, one has a projected distance of about 265 kpc from M31 and could be an intergalactic cluster.     

A new estimate of the galactic halo mass based on the kinematics of globular clusters

We calculated the energy distribution function for globular clusters in our Galaxy, using the inversion procedure first suggested by Eddington. If the halo mass distribution is of the formM _H=r ^1.21, then the observed data on the velocity dispersion of F-clusters can be explained, resulting an enclosed mass of 4.3×10¹¹ M within a galactocentric radius of 33 kpc.     

UBV photometry of clusters in M31

A critical review is given of all published photoelectricUBV photometry of star clusters in the Andromeda Nebula. Observations by Sharovet al. are shown to exhibit rather large random errors, but no systematic deviations from theUBV system.     

A survey of ultraviolet-bright sources behind the halo of M31

We have performed a wide-area ultraviolet (UV) imaging survey using the GALaxy Evolution eXplorer to search for bright, point-like UV sources behind M31's extended halo. Our survey consisted of 46 pointings covering an effective area of ≈50 deg², in both the far-UV and near-UV channels. We combined these data with optical R -band observations acquired with the WIYN Mosaic-1 imager on the Kitt Peak National Observatory 0.9-m WIYN telescope. An analysis of the brightness and colours of sources matched between our photometric catalogues yielded ≈100 UV-bright quasar candidates. We have obtained discovery spectra for 76 of these targets with the Kast spectrometer on the Lick 3-m telescope and confirmed 30 active galactic nuclei and quasars, 29 galaxies at   z > 0.02  including several early-type systems, 16 Galactic stars (hot main-sequence stars) and one featureless source previously identified as a BL Lac object. Future UV spectroscopy of the brightest targets with the Cosmic Origins Spectrograph on the Hubble Space Telescope will enable a systematic search for diffuse gas in the extended halo of M31.     

Density profiles and luminosity functions of the globular clusters M3 and M92

Tautenburg Schmidt plates with the globular clusters M3 and M92 were measured on the APM facility in Cambridge, mainly for astrometric purposes. The data were used to derive the radial density profiles and the luminosity functions of these clusters. There is a good agreement of our results with formerly ones derived by other authors. In both clusters effects of mass segregation are observed.     

Spectroscopic research with the Hartebeesthoek radio telescope

Research into star-forming regions, evolved HII regions, late-type stars with circumstellar dust shells and comet Halley using spectroscopic observations made with the Hartebeesthoek radio telescope is reviewed.     

Photographic UVB photometry of the globular clusters M 15 and NGC 6712

Photographic intermediate banduvb observations of RGB and some AGB stars in 7 × 7 arcmin fields centered on the globular clusters M 15 and NGC 6712 are obtained. The photometric data is not fully reduced to the standard system but it is converted in an unique instrumental system. The photometry confirms the existence of the gaps in the giant branch of M 15. For NGC 6712 the Stromgren colors show a bimodal distribution and point at a bimodal carbon abundance for the bright giants from the central part. The possibilities of theuvby system for a classification of RGB and AGB stars are briefly discussed.