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We describe the photometric calibration of the Lunar-based Ultraviolet Telescope (LUT), the first robotic astronomical telescope working on the lunar surface, for its first six months of operation on the lunar surface. Two spectral datasets (set A and B) from near-ultraviolet (NUV) to the optical band were constructed with 44 International Ultraviolet Explorer (IUE) standards, because of the LUT’s relatively wide wavelength coverage. Set A was obtained by extrapolating the IUE NUV spectra (λ < 3200 A ) to the optical band based upon the theoretical spectra of stellar atmosphere models. Set B was composed of theoretical spectra from 2000 A to 8000 A extracted from the same model grid. In total, seven standards have been observed in 15 observational runs until May 2014. The calibration results show that the photometric performance of LUT is highly stable in its first six months of operation. The magnitude zero points obtained from the two spectral datasets are also consistent with each other, i.e., zp = 17.54 ± 0.09 mag (set A) and zp = 17.52 ± 0.07 mag (set B).

A large telescope's adaptive optics (AO) system requires one or more bright artificial laser guide stars to improve its sky coverage. The recent advent of a high power sodium laser is perfect for such application. However, besides the output power, other parameters of the laser also have a significant impact on the brightness of the generated sodium laser guide star, mostly in non-linear relationships. When tuning and optimizing these parameters it is necessary to tune based on a laser guide star generation performance metric. Although return photon fluxis widely used, variability of the atmosphere and sodium layer makes it difficult to compare results from different sites or even within a short time period for the same site. A new metric, coupling efficiency, is adopted in our field tests. In this paper, we will introduce our method for measuring the coupling efficiency of a 20W class pulse sodium laser for AO application during field tests that were conducted during 2013–2015.

We present results of on-sky tests performed in the summer of 2013 to characterize the performance of a prototype high-power pulsed laser for adaptive optics. The laser operates at a pulse repetition rate (PRR) of 600–800[Formula: see text]Hz, with a 6% duty cycle. Its coupling efficiency was found to be, in the best test case (using 18[Formula: see text]W of transmitted power), [Formula: see text] photons s[Formula: see text] sr[Formula: see text] atom[Formula: see text] W[Formula: see text] m2 when circular polarization was employed and [Formula: see text] photons s[Formula: see text] sr[Formula: see text] atom[Formula: see text] W[Formula: see text] m2 with linear polarization. No improvement was seen when D[Formula: see text] repumping was used, but this is likely due to the relatively large laser guide star (LGS) diameter, typically 10 arcsec or more, which resulted in low irradiance levels. Strong relaxation oscillations were present in the laser output, which have the effect of reducing the coupling efficiency. To better understand the results, a physical modeling was performed using the measured pulse profiles and parameters specific to these tests. The model results, for a 10 arcsec angular size LGS spot, agree well with the observations. When extrapolating the physical model for a sub-arcsecond angular size LGS (typical of what is needed for a successful astronomical guide star), the model predicts that this laser would have a coupling efficiency of 130 photons s[Formula: see text] sr[Formula: see text] atom[Formula: see text] W[Formula: see text] m2, using circular polarization and D[Formula: see text] repumping, for a LGS diameter of 0.6 arcsec Full Width at Half Maximum (FWHM), and free of relaxation oscillations in the 589 nm laser light.

Tsinghua-NAOC (National Astronomical Observatories of China) Telescope (hereafter, TNT) is an 80-cm Cassegrain reflecting telescope located at Xinglong bservatory of NAOC, with main scientific goals of monitoring various transients in the universe such as supernovae, gamma-ray bursts, novae, variable stars, and active galactic nuclei. We present in this paper a systematic test and analysis of the photometric performance of this telescope. Based on the calibration observations on twelve photometric nights, spanning the period from year 2004 to year 2012, we derived an accurate transformation relationship between the instrumental $ubvri$ magnitudes and standard Johnson $UBV$ and Cousins $RI$ magnitudes. In particular, the color terms and the extinction coefficients of different passbands are well determined. With these data, we also obtained the limiting magnitudes and the photometric precision of TNT. It is worthwhile to point out that the sky background at Xinglong Observatory may become gradually worse over the period from year 2005 to year 2012 (e.g., $\sim$21.4 mag vs. $\sim$20.1 mag in the V band)., 12 pages,9 figures, accepted by RAA

In 2008 January the 24th Chinese expedition team successfully deployed the Chinese Small Telescope ARray (CSTAR) to Dome A, the highest point on the Antarctic plateau. CSTAR consists of four 14.5cm optical telescopes, each with a different filter (g, r, i and open) and has a 4.5°×4.5° field of view (FOV). Based on the CSTAR data, initial statistics of astronomical observational site quality and light curves of variable objects were obtained. To reach higher photometric quality, we are continuing to work to overcome the effects of uneven cirrus cloud cirrus, optical “ghosts” and intra-pixel sensitivity. The snow surface stability is also tested for further astronomical observational instrument and for glaciology studies.

GRB 090426 is a short duration burst detected by Swift ($T_{90}\sim 1.28$ s in the observer frame, and $T_{90}\sim 0.33$ s in the burst frame at $z=2.609$). Its host galaxy properties and some $\gamma$-ray related correlations are analogous to those seen in long duration GRBs, which are believed to be of a massive-star origin (so-called Type II GRBs). We present the results of its early optical observations with the 0.8-m TNT telescope at Xinglong observatory, and the 1-m LOAO telescope at Mt. Lemmon Optical Astronomy Observatory in Arizona. Our well-sampled optical afterglow lightcurve covers from $\sim 90$ seconds to $\sim 10^4$ seconds post the GRB trigger. It shows two shallow decay episodes that are likely due to energy injection, which end at $\sim 230$ seconds and $\sim 7100$ seconds, respectively. The decay slopes post the injection phases are consistent with each other ($\alpha\simeq 1.22$). The X-ray afterglow lightcurve appears to trace the optical, although the second energy injection phase was missed due to visibility constraints introduced by the {\em Swift} orbit. The X-ray spectral index is $\beta_X\sim 1.0$ without temporal evolution. Its decay slope is consistent with the prediction of the forward shock model. Both X-ray and optical emission is consistent with being in the same spectral regime above the cooling frequency ($\nu_c$). The fact that $\nu_c$ is below the optical band from the very early epoch of the observation provides a constraint on the burst environment, which is similar to that seen in classical long duration GRBs. We therefore suggest that death of a massive star is the possible progenitor of this short burst.

The THz spectral region includes a number of important transitions which allow us to trace the evolution of the interstellar medium. Because of the opacity of the atmosphere in this spectral range, the best sites for ground-based THz observations are on the Antarctic Plateau; of these sites, Dome A is expected to be the best. THz survey science can be carried out with small telescopes, easing logistical constraints. By deploying a submillimetre-wave tipper/ telescope to Dome A, we have trialled several technologies for such an instrument, and we are able to test whether the site quality is sufficient for THz surveys.

PLATO is a fully-robotic observatory designed for operation in Antarctica. It generates its own electricity (about 1 kW), heat (sufficient to keep two 10-foot shipping containers comfortably above 0°C when the outside temperature is at -70°C), and connects to the internet using the Iridium satellite system (providing ~30 MB/day of data transfer). Following a successful first year of operation at Dome A during 2008, PLATO was upgraded with new instruments for 2009.

The PLATeau Observatory (PLATO) is an automated self-powered astrophysical observatory that was deployed to Dome A, the highest point on the Antarctic plateau, in 2008 January. PLATO consists of a suite of site-testing instruments designed to quantify the benefits of the Dome A site for astronomy, and science instruments designed to take advantage of the unique observing conditions. Instruments include CSTAR, an array of optical telescopes for transient astronomy; Gattini, an instrument to measure the optical sky brightness and cloud cover statistics; DASLE, an experiment to measure the statistics of the meteorological conditions within the near-surface layer; Pre-HEAT, a submillimeter tipping radiometer measuring the atmospheric transmission and water vapor content and performing spectral line imaging of the Galactic plane; and Snodar, an acoustic radar designed to measure turbulence within the near-surface layer. PLATO has run completely unattended and collected data throughout the winter 2008 season. Here we present a detailed description of the PLATO instrument suite and preliminary results obtained from the first season of operation.

Dome A, the summit of the Antarctic plateau, is expected to have even better atmospheric conditions for ground-based astronomy than Dome C. However, the logistical constraints are very stringent. Current instrumentation at Dome A exemplifies the requirements im- posed by these constraints. Future instrumentation and infrastructure will exploit the qualities of the site much more fully.

We here report the photometric performance of Lunar-based Ultraviolet telescope (LUT), the first robotic telescope working on the Moon, for its 18-months operation. In total, 17 IUE standards have been observed in 51 runs until June 2015, which returns a highly stable photometric performance during the past 18 months (i.e., no evolution of photometric performance with time). The magnitude zero point is determined to be $17.53\pm0.05$ mag, which is not only highly consistent with the results based on its first 6-months operation, but also independent on the spectral type of the standard from which the magnitude zero point is determined. The implications of this stable performance is discussed, and is useful for next generation lunar-based astronomical observations., 6 pages, 3 figures and 2 tables. To be published in Ap&SS

IRAS 04000+5052 appears to be a single, somewhat extended red source on optical CCD images. From our infrared imaging observations, an infrared cluster consisting of 15 objects is discovered in this region. In this paper, by discussing and analyzing the observational results of near-infrared imaging, optical spectroscopy, and the 12CO molecular line, together with IRAS and NRAO VLA Sky Survey (NVSS) data, we conclude that IRAS 04000+5052 is a compact H II region with a very young dense stellar cluster. The spectrum of the compact H II region shows that it is a metal-poor nebula, which has the lowest line ratio of [N II]/Hα (~1/16.3) discovered in the H II regions of our Galaxy until now. There are three possible explanations. The first is a Herbig Be star model, the second suggests that the material constituting this nebula could come from some nearby external galaxy from accretion of galaxies, and the third suggests that the material was produced in the primeval phase of our Galaxy and has not been chemically contaminated much. There exists an undetected gap between K = 13.6 and the detection limit of 16.2 mag. We give two possible interpretations for this undetected gap; one is based on the star formation itself, and the other is a possible observational effect. This infrared cluster is a very small (0.83 pc × 1.55 pc ) and isolated high-mass protostellar cluster, in which there is a B0.5-type star exciting the compact H II region. The derived heliocentric distance (~4.29 kpc) of IRAS 04000+5052 is twice as large as that of the Perseus arm. It is located far beyond the Perseus arm at the direction (l = 150.86).

87 stars in the NGC 6913 field with both UBV and Vilnius photometry are selected to be the sample. The membership probability of the stars is greater than 50%. The correlation among Vilnius photometry, UBV photometry and reddening in the cluster is reviewed. It is found that the photometry in the Vilnius X, Y and Z bands can be used to make rough spectral classification. The values of E( B-V ) are well correlated with the Vilnius colors of X-Y, Y-Z, Z-V and V-S in NGC 6913. The ratio of ( V-S )/( Y-Z ) of the MPCM (Most Possible Cluster Members) is a constant (1.30 ∼ p0.06), and has no effect on the values of E( B-V ), ( B-V ) 0 and V 0 . Comparing with the observational data of all the stars of NGC 6913 region, we propose that the value of ( V-S )/( Y-Z ) can probably be used to select the preliminary candidates of one open cluster. In addition, 12 variable stars are discovered in the NGC 6913 region, in which star #155 has a variation with an amplitude of 4.25 mag.

For investigating the statistical properties of X-ray selected Active Galactic Nuclei (AGNs), we have carried out a program of optical identification of a selection of X-ray sources from ROSAT All Sky Survey Bright Source Catalogue (RASS-BSC) using the 2.16 m telescope of Beijing Astronomical Observatory (BAO). In the preliminary observations, 23 new AGNs were discovered, of which 9 are quasars, and 14 are Seyfert galaxies.

Optical spectroscopic identification of X-ray selected WTTS (weak emission-line T Tauri stars) candidates in the Taurus-Auriga outskirts on the basis of ROSAT pointing observations, has resulted in the discovery of 4 WTTS and several other Li-rich sources. This paper gives the R magnitudes, coordinates (J2000) from USNO (V1.0), spectral type classifications, equivalent widths of Li I absorption and H α emission lines of all the X-ray sources investigated, and the proper motions and parallaxes of some of them, as well as the spectra of the newly discovered WTTS. For the first time, the spatial distribution of a rather complete, ROSAT-discovered sample of WTTS, including those identified from the ROSAT All-Sky Survey and PSPC pointing observations around one of the nearby star-forming regions has been provided, together with a preliminary analysis.

PLATO is a 6 tonne completely self-contained robotic observatory that provides its own heat, electricity, and satellite communications. It was deployed to Dome A in Antarctica in January 2008 by the Chinese expedition team, and is now in its second year of operation. PLATO is operating four 14.5cm optical telescopes with 1k × 1k CCDs, a wide-field sky camera with a 2k × 2k CCD and Sloan g, r, i filters, a fibre-fed spectrograph to measure the UV to near-IR sky spectrum, a 0.2m terahertz telescope, two sonic radars giving 1m resolution data on the boundary layer to a height of 180m, a 15m tower, meteorological sensors, and 8 web cameras. Beginning in 2010/11 PLATO will be upgraded to support a Multi Aperture Scintillation Sensor and three AST3 0.5m schmidt telescopes, with 10k × 10 CCDs and 100TB/annum data requirements.

We present calibrated photometric measurements of the earliest detections of nearby type Ia supernovae (SNe Ia). The set of ~30 new, unfiltered CCD observations delineate the early rise behavior of SNe Ia > 18 to 10 days before maximum. Using simple empirical models, we demonstrate the strong correlation between the risetime (i.e., the time between explosion and maximum), the post-rise light-curve shape, and the peak luminosity. Using a variety of light-curve shape methods, we find the risetime to B maximum for a SN Ia with Delta m15(B)=1.1 mag and peak M_V=-19.45 mag to be 19.5+/-0.2 days. We find that the peak brightness of SNe Ia is correlated with their risetime; SNe Ia which are 0.10 mag brighter at peak in the B-band require 0.80+/-0.05 days longer to reach maximum light. We determine the effects of several possible sources of systematic errors, but none of these significantly impacts the inferred risetime. Constraints on SN Ia progenitor systems and explosion models are derived from a comparison between the observed and theoretical predictions of the risetime.

Using the new data from Hipparcos and the TD-1 UV data, we fix the positions of three objects, HD 104237, HD 100546 and ϵ Cha in the HR diagram and discuss their theoretical evolutionary status.

We have observed the spectra of 20 little researched cataclysmic variables (CVs) or objects that have been classified as such. We have identified 13 (65%) as CVs and consider the other 7 as unlikely to be CVs. (Table 1, Col. 8). Using more material than previous authors had, we have identified 1 DA type white dwarf and 4 binary systems, together with the spectral types of the components. Our new data does not support the previous classification of Herbig Ae/Be star for FY Per; rather, it should be a CV. For PG 1712+493 we have isolated the spectra of the central O-type star and the surrounding nebula.

We present spectroscopic and photometric results of SN 1996cb. The supernova was independently discovered in NGC 3510 by M. Aoki, T. Cho, & K. Toyama of Japan and Qiao et al. of Beijing Astronomical Observatory on 1996 December 15 and 18, respectively. The results cover about 6 months following the discovery. The first few spectra showed strong Balmer lines with obvious P Cygni profiles, offering evidence of a Type II supernova. The emergence of He I lines could be inferred in these spectra. That the He I lines became quite prominent in the spectra near optical maximum confirmed that SN 1996cb was definitely a Type IIb supernova, like SN 1987K and SN 1993J. The photometric results showed that the B-I color evolution was very similar to that of SN 1993J. Comparing two color curves, we were able to estimate that the explosion of SN 1996cb occurred on UT 1996 December 12. Although the overall light curves resembled that of SN 1993J, they showed some differences, especially for the B band. SN 1996cb had a broad peak in the light curves, and it declined somewhat slowly and, compared with SN 1993J, exhibited a plateau-like shape between 20 and 50 days after the maximum for the B and V bands. This indicates that there was relatively more hydrogen in the outer envelope of the progenitor of SN 1996cb. The spectral evolution of SN 1996cb displayed further differences from SN 1993J. In the case of SN 1996cb, the Balmer lines showed strong P Cygni profiles at a very early time, resembling the early spectra of SN 1987A, a supernova resulting from a compact blue supergiant star. The dramatic changes of expansion velocities at early times indicated that the photosphere of SN 1996cb receded more quickly than it did in SN 1993J. The He I lines emerged much earlier and evolved more dramatically, causing SN 1996cb to display the features of a Type Ib supernova before maximum. This might be the result of a dramatic recession of the photosphere at an early time; the He I lines and [O I] lines showed conspicuous blueshifts when they emerged, resembling the blueshifts of the [O I] lines that appeared in the late spectra of SN 1993J. This is probably observational evidence of Rayleigh-Taylor instabilities occurring at the interfaces between the H and He and the He and O+C layers, respectively; Hα emission and absorption components, especially the latter, were conspicuous 100 days after the explosion. We also conclude that the outer envelope of SN 1996cb had relatively more hydrogen than was the case for SN 1993J, even though the amount remained much less than is typical of other Type II supernovae. This finding is consistent with the results of the photometry. The [O I] and O lines emerged very late and exhibited weak emission, indicating that the He-rich layer was relatively thick. Combining the analyses of photometric and spectroscopic evolution, we conclude that the progenitor of SN 1996cb, like that of SN 1993J, was a stripped massive star exhibiting some special features: it was probably a more compact star with a thick helium layer and a relatively more massive hydrogen envelope.

In order to investigate selection criteria for a ROSAT X-ray selected sky survey of bright nearby quasars, test observations were carried out on the 2.16 m telescope of Beijing Observatory between 1995 April and 1996 October. In the process 73 quasars, 27 Seyferts. 1 BL Lac candidate, 1 white dwarf and 1 cataclysmic variable were discovered.

By dividing the total energy radiated from the photosphere of a supernovae into a large number of photon packets and then following them in their outward journey, we overcome the problem of line blanketing encountered in usual simulation work. With supporting programs providing the density and abundance distributions in the envelope, our software package can be effectively used for a study of the early spectrum of supernovae. We give an application to the observed spectrum of SN 1993J on 1993-04-13.

We present the modeling of the ultraviolet and optical spectra obtained simultaneously on 1993 April 15 with the HST and at Lick Observatory. A Monte Carlo code is employed in the modeling and a comparison is made between models reported by different groups. With an atmosphere similar to the Sun in chemical composition, the observed spectral lines are well reproduced by a power law density structure of index around 20 except the strong Hα and HeI λ5876 lines which have peculiar absorption profiles. The photospheric velocity is found to be 9500 km/s and the blackbody temperature of the spectrum is 7990 K. For Hα and HeI λ5876, we suggest a two-component density structure which has a smoother layer located immediately outside the steeply decreasing inner envelope. The power law indices are most probably 20 and 3, respectively, with the transition point at about 13 000 km/s. In addition, this outer smooth layer serves to flatten the far UV spectrum as observed.

We present a catalogue including 11,204 spectra for 10,436 early-type emission-line stars from LAMOST DR2, among which 9,752 early-type emission-line spectra are newly discovered. For these early-type emission-line stars, we discuss the morphological and physical properties from their low-resolution spectra. In this spectral sample, the H$\alpha$ emission profiles display a wide variety of shapes. Based on the H$\alpha$ line profiles, these spectra are categorized into five distinct classes: single-peak emission, single-peak emission in absorption, double-peak emission, double-peak emission in absorption, and P-Cygni profiles. To better understand what causes the H$\alpha$ line profiles, we divide these objects into four types from the view of physical classification, which include classical Be stars, Herbig Ae/Be stars, close binaries and spectra contaminated by HII regions. The majority of Herbig Ae/Be stars and classical Be stars are identified and separated using the (H-K, K-W1) color-color diagram. We also discuss thirty one binary systems as listed in SIMBAD on-line catalogue and identify 3,600 spectra contaminated by HII regions after cross matching with positions in the Dubout-Crillon catalogue. A statistical analysis of line profiles versus classifications is then conducted in order to understand the distribution of H$\alpha$ profiles for each type in our sample. Finally, we also provide a table of 172 spectra with FeII emission lines and roughly calculate stellar wind velocities for seven spectra with P-Cygni profiles., Comment: 18 pages, 10 figures and 4 tables

In this paper the Kurucz stellar atmosphere model is fitted to the observed IUE, IRAS, ground-based optical and near-infrared data of 22 Herbig Ae/Be stars. A statistical analysis is made based on energy balance between the central star and the circumstellar shell. It is concluded that the shells are disk-shaped.

From June 19 to August 27, using the 2.16m telescope in the Beijing Astronomical Observatory, we obtained some low resolution spectra of SN1993J. The forbidden emission lines [O I], [Ca II] were very strong and dominated the spectra. However, the Hα and He lines were very weak. Many fine structures appeared in the Hα and [O I] lines. We found that the supernova had entered the nebular phase and strong instability and chemical mixing had occurred in the ejecta.

Using 2.16m telescope with CCD system at Xinglong station of Beijing Astronomical Observatory, IRAS 04000+5052 has been observed at VRI bands respectively. The R-filter image of the source shows very distinct extension feature. Radiation of the source at R band is much stronger than that at V and I bands. By using the 1.26m infrared telescope, a large variation at near infrared bands was also found. From the IRAS fluxes and LRS spectrum, as well as the morphology of the source, we conclude that it may possibly be a young object in the process forming new stars.

The i-band observing conditions at Dome A on the Antarctic plateau have been investigated using data acquired during 2008 with the Chinese Small Telescope Array. The sky brightness, variations in atmospheric transparency, cloud cover, and the presence of aurorae are obtained from these images. The median sky brightness of moonless clear nights is 20.5 mag arcsec−2 in the SDSS i band at the south celestial pole (which includes a contribution of about 0.06 mag from diffuse Galactic light). The median over all Moon phases in the Antarctic winter is about 19.8 mag arcsec−2. There were no thick clouds in 2008. We model contributions of the Sun and the Moon to the sky background to obtain the relationship between the sky brightness and transparency. Aurorae are identified by comparing the observed sky brightness to the sky brightness expected from this model. About 2% of the images are affected by relatively strong aurorae.

The Chinese Small Telescope ARray (hereinafter CSTAR) is the first Chinese astronomical instrument on the Antarctic ice cap. The low temperature and low pressure testing of the data acquisition system was carried out in a laboratory refrigerator and on the 4500m Pamirs high plateau, respectively. The results from the final four nights of test observations demonstrated that CSTAR was ready for operation at Dome A, Antarctica. In this paper we present a description of CSTAR and the performance derived from the test observations., Accepted Research in Astronomy and Astrophysics (RAA) 1 Latex file and 20 figures

In 2008 January the 24th Chinese expedition team successfully deployed the Chinese Small Telescope ARray (CSTAR) to DomeA, the highest point on the Antarctic plateau. CSTAR consists of four 14.5cm optical telescopes, each with a different filter (g, r, i and open) and has a 4.5degree x 4.5degree field of view (FOV). It operates robotically as part of the Plateau Observatory, PLATO, with each telescope taking an image every 30 seconds throughout the year whenever it is dark. During 2008, CSTAR #1 performed almost flawlessly, acquiring more than 0.3 million i-band images for a total integration time of 1728 hours during 158 days of observations. For each image taken under good sky conditions, more than 10,000 sources down to 16 mag could be detected. We performed aperture photometry on all the sources in the field to create the catalog described herein. Since CSTAR has a fixed pointing centered on the South Celestial Pole (Dec =-90 degree), all the sources within the FOV of CSTAR were monitored continuously for several months. The photometric catalog can be used for studying any variability in these sources, and for the discovery of transient sources such as supernovae, gamma-ray bursts and minor planets., Comment: 1 latex file and 9 figures The paper is accepted by PASP

A gamma-ray burst (GRB) optical photometric follow-up system at the Xinglong Observatory of National Astronomical Observatories of China (NAOC) has been constructed. It uses the 0.8-m Tsinghua-NAOC Telescope (TNT) and the 1-m EST telescope, and can automatically respond to GRB Coordinates Network (GCN)alerts. Both telescopes slew relatively fast, being able to point to a new target field within about 1 min upon a request. Whenever available, the 2.16-m NAOC telescope is also used. In 2006, the system responded to 15 GRBs and detected seven early afterglows. In 2007, six GRBs have been detected among 18 follow-up observations. TNT observations of the second most distant GRB 060927 (z=5.5) are shown, which started as early as 91s after the GRB trigger. The afterglow was detected in the combined image of first 19x20s unfiltered exposures. This GRB follow-up system has joined the East-Asia GRB Follow-up Observation Network (EAFON)., Comment: Published in ChJAA, 2008, 8, 693 (accepted 2008 March 27); 8 pages, 2 figures, 2 tables

We give a catalogue of early-type emission-line stars with V−[25]⩾8, obtained by cross-identification between Wackerling's catalogue and the IRAS catalogue of point sources. A study of the distribution in space of the stars show that these stars belong to the extreme Population I, thus the present compilation provides a rather complete sample for further study of the evolution of pre- and post-main sequence stars of medium and high masses.

We have developed an empirical and effective set of criteria, based on the 2MASS colors, to select candidate classical T Tauri stars (CTTS). This provides a useful tool to study the young stellar population in star-forming regions. Here we present our analysis of the bright-rimmed clouds (BRCs) B 35, B 30, IC 2118, LDN 1616, LDN 1634, and Orion East to show how massive stars interact with molecular clouds to trigger star formation. Our results support the radiation-driven implosion model in which the ionization fronts from OB stars compress a nearby cloud until the local density exceeds the critical value, thereby inducing the cloud to collapse to form stars. We find that only BRCs associated with strong IRAS 100 micron emission (tracer of high density) and H-alpha emission (tracer of ionization fronts) show signs of ongoing star formation. Relevant timescales, including the ages of O stars, expanding HII regions, and the ages of CTTS, are consistent with sequential star formation. We also find that CTTS are only seen between the OB stars and the BRCs, with those closer to the BRCs being progressively younger. There are no CTTS leading the ionization fronts, i.e., within the molecular clouds. All these provide strong evidence of triggered star formation and show the major roles massive stars play in sustaining the star-forming activities in the region., Comment: To appear in ApJ

Part results of optical observations made at Fuzhou and Urumqi during the period of Comet Shoemaker-Levy impacts on Jupiter (1994 July 17–22), are given in this Note.

We present photometry of 12 recent supernovae (SNe) recovered in a {\it Hubble Space Telescope} Snapshot program, and tie the measurements to earlier ground-based observations, in order to study the late-time evolution of the SNe. Many of the ground-based measurements are previously unpublished, and were made primarily with a robotic telescope, the Katzman Automatic Imaging Telescope. Evidence for circumstellar interaction is common among the core-collapse SNe. Late-time decline rates for Type IIn SNe are found to span a wide range, perhaps due to differences in circumstellar interaction. An extreme case, SN IIn 1995N, declined by only 1.2 mag in $V$ over about 4 years following discovery. Template images of some SNe must therefore be obtained many years after the explosion, if contamination from the SN itself is to be minimized. Evidence is found against a previous hypothesis that the Type IIn SN 1997bs was actually a superoutburst of a luminous blue variable star. The peculiar SN Ic 1997ef, a "hypernova," declined very slowly at late times. The decline rate of the SN Ia 2000cx decreased at late times, but this is unlikely to have been caused by a light echo., Comment: 6 figures. Accepted by PASP

1RXS J232953.9+062814 was identified as a cataclysmic variable by Wei et al. (1999). Four low-resolution spectra of 1RXS J232953.9+062814 were obtained by using the 2.16-m telescope of the National Astronomical Observatories, in which two of them were at outburst, and the other two were at quiescence. The system is about 16.8 B and 16.5 V at quiescence, and 12.6 B and 12.6 V at outburst. The quiescent spectra were dominated by double-peaked Balmer emissions, which indicates a hydrogen-rich system with a high-inclination accretion disc. MgH and TiO absorption bands appeared in the quiescent spectrum imply a companion with a spectral type of early M dwarf. If we take it as a M0 dwarf, the system is located at a distance of 350 pc with a proper motion velocity 150 km s$^{-1}$. The superhump period of 0.046311 days (Uemura et al. 2001) was confirmed by our V photometry. The short period and the hydrogen-rich nature reveal that this system is another SU Ursae Majoris-type dwarf nova below the period minimum after V485 Centauri. 1RXS J232953.9+062814 is one of the most important systems for studying the evolutionary scenario of cataclysmic variables since it is much brighter than V485 Cen., 4 pages, 2 figures, accepted by Chin. J. Astron. Astrophys

We have compiled a sample of 45 Type Ia supernovae (SNe Ia) discovered by the Lick Observatory Supernova Search (LOSS) and the Beijing Astronomical Observatory Supernova Survey (BAOSS), and determined the rate of spectroscopically peculiar SNe Ia (i.e., SN 1986G-like, SN 1991bg-like, and SN 1991T-like objects) and the luminosity function of SNe Ia. Because of the nature of the two surveys (distance-limited with small baselines and deep limiting magnitudes), nearly all SNe Ia have been discovered in the sample galaxies of LOSS and BAOSS; thus, the observed peculiarity rate and luminosity function of SNe Ia are intrinsic. We find that 36$\pm$9% of nearby SNe Ia are peculiar; specifically, the luminosity function of SNe Ia consists of 20% SN 1991T-like, 64% normal, and 16% SN 1991bg-like objects. We have compared our results to those found by earlier studies, and to those found at high redshift. The apparent dearth of SN 1991T-like objects at high redshift may be due to extinction, and especially to the difficulty of recognizing them from spectra obtained past maximum brightness or from spectra with low signal-to-noise ratios. Implications of the high peculiarity rate for the progenitor systems of SNe Ia are also briefly discussed., Comment: 20 pages, 7 figures, accepted for publication in the ApJ

The energy source has remained to be the great mystery in understanding of the gamma-ray bursts (GRBs) if the events are placed at cosmological distances as indicated by a number of recent observations. The currently popular models include (1)the merger of two neutron stars or a neutron star and a black hole binary and (2)the hypernova scenario of the collapse of a massive member in a close binary. Since a neutron star will inevitably collapse into a black hole if its mass exceeds the limit $M_{max}\approx3M_{\odot}$, releasing a total binding gravitational energy of $\sim10^{54}$ erg, we explore semi-empirically the possibility of attributing the energy source of GRB to the accretion- induced collapse of a neutron star (AICNS) in a massive X-ray binary system consisting of a neutron star and a type O/B companion. This happens because a significant mass flow of $\sim10^{-3}$--$10^{-4}M_{\odot}$ yr$^{-1}$ may be transferred onto the neutron star through the Roche-lobe overflow and primarily during the spiral-in phase when it plunges into the envelope of the companion, which may eventually lead to the AICNS before the neutron star merges with the core of the companion. In this scenario, a ``dirty'' fireball with a moderate amount of beaming is naturally expected because of the nonuniformity of the stellar matter surrounding the explosion inside the companion, and a small fraction ($\sim0.1%$) of the energy is sufficient to create the observed GRBs. In addition, the bulk of the ejecting matter of the companion star with a relatively slow expansion rate may act as the afterglow. Assuming a non-evolutionary model for galaxies, we estimate that the birthrate of the AICNS events is about 2 per day within a volume to redshift $z=1$ for an $\Omega_0=1$ universe, consistent with the reported GRB rate., Comment: 4 pages, no figures, emulateapj.sty, to appear in ApJ Letters, several paragraphs added, references added and updated

Hu et al (1993) have selected a sample of proto-planetary nebula candidates based on the IRAS color-color diagram. IRAS 01005+7910 is one object of this sample. We have observed this object photometrically (Table 1) and spectroscopically (Fig. 1). From its spectral type of B2I and optical color of B - V = 0.23, we can derive the reddening as E(B - V) = 0.39 and interstellar/circumstellar absorption Av = 1.20. If it is a normal B-type supergiant, the distance module will be m - M = 16.05 and distance d = 16.2 kpc. Due to the galactic latitude b = 16.6, it should be located at about 4.6 kpcabove the galactic plane. This does not fit with normal B-type supergiant and we considered that it is a post-AGB star located at high galactic latitude. Recently Hrivnak et al (2000) found that this object shows carbon-rich features in the infrared. A paper on observations, reduction and discussions of this object has been submitted to the Chinese Journal of Astronomy and Astrophysics.

In our observations of the young open star cluster NGC 6913, we discovered a star with a peculiar variation in its Hα profile. A preliminary analysis of the data is given.

Continuous spectrascqpic observations of SN1993J have been conducted in Beijing Observatory's 2. 16 meter telescope. We discuss in this letter the data obtained from April 7 to May 5, 1993. Investigations of the time evolution of the various absorption and emission lines show that the supernova debris is not spherically symmetric. Possible structures are discussed.