10 research outputs found
The atmospheric dispersion corrector for the Large Sky Area Multi--object Fibre Spectroscopic Telescope (LAMOST)
The Large Sky Area Multi--object Fibre Spectroscopic Telescope (LAMOST) is
the largest (aperture 4 m) wide field of view (FOV) telescope and is equipped
with the largest amount (4000) of optical fibres in the world. For the LAMOST
North and the LAMOST South the FOV are 5 deg and 3.5 deg, the linear diameters
are 1.75 m and 1.22 m, respectively. A new kind of atmospheric dispersion
corrector (ADC) is put forward and designed for LAMOST. It is a segmented lens
which consists of many lens--prism strips. Although it is very big, its
thickness is only 12 mm. Thus the difficulty of obtaining big optical glass is
avoided, and the aberration caused by the ADC is small. Moving this segmented
lens along the optical axis, the different dispersions can be obtained. The
effects of ADC's slits on the diffraction energy distribution and on the
obstruction of light are discussed. The aberration caused by ADC is calculated
and discussed. All these results are acceptable. Such an ADC could also be used
for other optical fibre spectroscopic telescopes, especially those which a have
very large FOV.Comment: 14 pages, 8 figures, Accepted for publication in MNRA
The First Release of the CSTAR Point Source Catalog from Dome A, Antarctica
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 PAS
The sky brightness and transparency in i-band at Dome A, Antarctica
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
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.Comment: There are 1 Latex file and 14 figures accepted by A
Progress and results from the chinese small telescope ARray (CSTAR)
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.8 page(s