We present measurements of dust reddening using the colors of stars with spectra in the Sloan Digital Sky Survey. We measure reddening as the difference between the measured and predicted colors of a star, as derived from stellar parameters from the Sloan Extension for Galactic Understanding and Exploration Stellar Parameter Pipeline. We achieve uncertainties of 56, 34, 25, and 29 mmag in the colors u – g, g – r, r – i, and i – z, per star, though the uncertainty varies depending on the stellar type and the magnitude of the star. The spectrum-based reddening measurements confirm our earlier "blue tip" reddening measurements, finding reddening coefficients different by –3%, 1%, 1%, and 2% in u – g, g – r, r – i, and i – z from those found by the blue tip method, after removing a 4% normalization difference. These results prefer an RV = 3.1 Fitzpatrick reddening law to O'Donnell or Cardelli et al. reddening laws. We provide a table of conversion coefficients from the Schlegel et al. (SFD) maps of E(B – V) to extinction in 88 bandpasses for four values of RV , using this reddening law and the 14% recalibration of SFD first reported by Schlafly et al. and confirmed in this work.

https://iopscience.iop.org/article/10.1088/0004-637X/737/2/103/pdf

Measuring Reddening with Sloan Digital Sky Survey Stellar Spectra and Recalibrating SFD

The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST, also called the Guo Shou Jing Telescope) is a special reflecting Schmidt telescope. LAMOST's special design allows both a large aperture (effective aperture of 3.6 m–4.9 m) and a wide field of view (FOV) (5°). It has an innovative active reflecting Schmidt configuration which continuously changes the mirror's surface that adjusts during the observation process and combines thin deformable mirror active optics with segmented active optics. Its primary mirror (6.67 m × 6.05 m) and active Schmidt mirror (5.74m × 4.40m) are both segmented, and composed of 37 and 24 hexagonal sub-mirrors respectively. By using a parallel controllable fiber positioning technique, the focal surface of 1.75 m in diameter can accommodate 4000 optical fibers. Also, LAMOST has 16 spectrographs with 32 CCD cameras. LAMOST will be the telescope with the highest rate of spectral acquisition. As a national large scientific project, the LAMOST project was formally proposed in 1996, and approved by the Chinese government in 1997. The construction started in 2001, was completed in 2008 and passed the official acceptance in June 2009. The LAMOST pilot survey was started in October 2011 and the spectroscopic survey will launch in September 2012. Up to now, LAMOST has released more than 480000 spectra of objects. LAMOST will make an important contribution to the study of the large-scale structure of the Universe, structure and evolution of the Galaxy, and cross-identification of multi-waveband properties in celestial objects.

https://iopscience.iop.org/article/10.1088/1674-4527/12/9/003/pdf

The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST)

LAMOST (Large sky Area Multi-Object fiber Spectroscopic Telescope) is a Chinese national scientific research facility operated by National Astronomical Observatories, Chinese Academy of Sciences (NAOC). After two years of commissioning beginning in 2009, the telescope, instruments, software systems and operations are nearly ready to begin the main science survey. Through a spectral survey of millions of objects in much of the northern sky, LAMOST will enable research in a number of contemporary cutting edge topics in astrophysics, such as discovery of the first generation stars in the Galaxy, pinning down the formation and evolution history of galaxies — especially the Milky Way and its central massive black hole, and looking for signatures of the distribution of dark matter and possible sub-structures in the Milky Way halo. To maximize the scientific potential of the facility, wide national participation and international collaboration have been emphasized. The survey has two major components: the LAMOST ExtraGAlactic Survey (LEGAS) and the LAMOST Experiment for Galactic Understanding and Exploration (LEGUE). Until LAMOST reaches its full capability, the LEGUE portion of the survey will use the available observing time, starting in 2012. An overview of the LAMOST project and the survey that will be carried out in the next five to six years is presented in this paper. The science plan for the whole LEGUE survey, instrumental specifications, site conditions, and the descriptions of the current on-going pilot survey, including its footprints and target selection algorithm, will be presented as separate papers in this volume.

https://iopscience.iop.org/article/10.1088/1674-4527/12/7/002/pdf

LAMOST spectral survey — An overview

We demonstrate a novel technology that combines the power of the multi-object spectrograph with the spatial multiplex advantage of an integral field spectrograph (IFS). The SydneyAAO (Australian Astronomical Observatory) Multi-object IFS (SAMI) is a prototype widefield system at the Anglo-Australian Telescope (AAT) that allows 13 imaging fibre bundles (‘hexabundles’) to be deployed over a 1-degree diameter field of view. Each hexabundle comprises 61 lightly fused multi-mode fibres with reduced cladding and yields a 75 per cent filling factor. Each fibre core diameter subtends 1.6 arcsec on the sky and each hexabundle has a field of view of 15 arcsec diameter. The fibres are fed to the flexible AAOmega double-beam spectrograph, which can be used at a range of spectral resolutions (R = λ/δλ ≈ 1700–13 000) over the optical spectrum (3700–9500 A). We present the first spectroscopic results obtained with SAMI for a sample of galaxies at z ≈ 0.05. We discuss the prospects of implementing hexabundles at a much higher multiplex over wider fields of view in order to carry out spatially resolved spectroscopic surveys of 10 4 –10 5 galaxies.

/pdf/the-sydney-aao-multi-object-integral-field-spectrograph-2jt8r4ekm4.pdf

The Sydney-AAO Multi-object Integral field spectrograph

Using the "standard pair" technique of paring stars of almost nil and high extinction but otherwise of almost identical stellar parameters from the SDSS, and combing the SDSS, GALEX, 2MASS and WISE photometry ranging from the far UV to the mid-IR, we have measured dust reddening in the FUV-NUV, NUV-u, u-g, g-r, r-i, i-z, z-J, J-H, H-Ks, Ks-W1 and W1-W2 colors for thousands of Galactic stars. The measurements, together with the E(B-V) values given by Schlegel et al. (1998), allow us to derive the observed, model-free reddening coefficients for those colors. The results are compared with previous measurements and the predictions of a variety of Galactic reddening laws. We find that 1) The dust reddening map of Schlegel et al. (1998) over-estimates E(B-V) by about 14 per cent, consistent with the recent work of Schlafly et al. (2010) and Schlafly & Finkbeiner (2011); 2) All the new reddening coefficients, except those for NUV-u and u-g, prefer the R(V) = 3.1 Fitzpatrick reddening law rather than the R(V) = 3.1 CCM and O'Donnell (O'Donnell 1994) reddening laws. Using the Ks-band extinction coefficient predicted by the R(V) = 3.1 Fitzpatrick law and the observed reddening coefficients, we have deduced new extinction coefficients for the FUV, NUV, u, g, r, i, z, J, H, W1 and W2 passbands. We recommend that the new reddening and extinction coefficients should be used in the future and an update of the Fitzpatrick reddening law in the UV is probably necessary. We stress however that the FUV- and NUV-band coefficients should be used with caution given their relatively large measurement uncertainties. Finally, potential applications of the "standard pair" technique with the LAMOST Galactic surveys are discussed.

Empirical extinction coefficients for the GALEX, SDSS, 2MASS and WISE passbands

A special reflecting Schmidt telescope is used to observe celestial objects The telescope has an aperture of 4m, f ratio of 5, and a 5° field of view Its optical axis is fixed and tilted 25° to the horizontal that runs from south to north The celestial objects were observed for 15 h as they passed through the meridian The shape of the reflecting Schmidt plate has to be changed with each different declination δ and in the tracking process This is achieved with active optics The sky area to be observed is -10° ≤ δ ≤ +90° There are plans to place ~4000 optical fibers on the telescope focal surface that will lead to a dozen spectrographs

Special configuration of a very large Schmidt telescope for extensive astronomical spectroscopic observation

The optical system of LAMOST is a special reflecting Schmidt system. It has an aperture of 4 m, f ratio of 5 and a 5 degree(s) field of view. The main optical axis is fixed on the meridian plane and tilted 25 degree(s) to the horizontal from south to north. The celestial objects were observed for 1.5 hours when they pass through the meridian. The reflecting Schmidt plane, MA, and the spherical mirror, MB, are segmented mirrors. MB is fixed on the foundation. The shape of the reflecting Schmidt plate has to be changed with different declination (delta) and in the tracking process. This is achieved with active optics. About 4000 optical fibers are planed to put on the focal surface. Some key technologies for LAMOST have been studied and presented in this paper: the calculation and testing method for thin mirror and segmented mirror active optics; the preliminary calculation and the experiment for active optics; the simulated calculation for optical image quality in 1.5 hours observation; a preliminary design of the alt-azimuth mounting and tracking system of MA.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Large-sky-area multiobject fiber spectroscopic telescope (LAMOST) and its key technology

This paper presents the recent progress in the optical system of LAMOST project: (1) The image quality at the edge of the field of view and the worst sky area is about 1.76 arc seconds. To improve this value, many aspherical lenses with 3 mm in diameter will be attached to some of 4000 optical fibers. With maximum 6.6 microns asphericity, these lenses could compensate the residual off-axis aberration of the optical system and obtain much better image quality, thus in any case the image quality could less than 0.6 arc seconds in diameter. (2) At the open air, an outdoor experiment program for creating the aspherical surface and accurately measuring the wave front shape of the active Schmidt correcting plate, which is with the full scale of the sub-system of the telescope, is introduced here. (3) Some further consideration and modification for the active support of each sub-mirror of the Schmidt correcting plate is discussed also in this paper. The presentation in this paper showed that the LAMOST is very likely to get much better quality even it is with a very large field of view, and its key technology - active optics is also reaching the realization.

Progress in LAMOST optical system

This paper presents the recent progress in the optical system of LAMOST project: (1) The image quality at the edge of the field of view and the worst sky area is about 176 arc seconds To improve this value, many aspherical lenses with 3 mm in diameter will be attached t some of 4000 optical fibers With maximum 66 microns asphericity, these lenses could compensate the residual off-axis aberration of the optical system and obtain much better image quality, thus in any case the image quality could less than 06 arc seconds in diameter (2) At the open air, an outdoor experiment program for creating the aspherical surface and accurately measuring the wave front shape of the active Schmidt correcting plate, which is with the full scale of the sub-system of the telescope, is introduced here (3) Some further consideration and modification for the active support of each sub-mirror of the Schmidt correcting plate is discussed also in this paper The presentation in this paper showed that the LAMOST is very likely to get much better quality even it is with a very large field of view, and its key technology--active optics is also reaching the realization

Progress in the LAMOST optical system

In this paper four 30 m to 100 m telescope configurations are put forward. (1) A transit mounting telescope with spherical primary mirror which can be rotated continuously only around the level axis, and a corrector on the prime focus is used to track the objects during they passing through the meridian cycle about 1.5 hours. (2) The mounting is the same as the first one, but to get higher image quality and smaller corrector, we applied the idea, which Su et al put forward in 1986, to actively change the shape of the area in use on the primary mirror during tracking in this telescope. (3) The third one is a fully fixed mounting telescope, but it is composed of several telescopes like the first or the second configuration in parallel along south and north direction. (4) An alt-az mounting telescope with a f/0.6 aspherical primary mirror. There are three important ideas in this paper: (a) transit mounting; (b) primary mirror with continuous variable shape during observation; (c) very fast f ratio telescope with fixed shape aspherical primary mirror. All these configurations can be used in optical, infrared, sub-millimeter and radio telescopes and also can be used on the moon.

Ding-qiang Su

Papers

Special configuration of a very large Schmidt telescope for extensive astronomical spectroscopic observation

Large-sky-area multiobject fiber spectroscopic telescope (LAMOST) and its key technology

Progress in LAMOST optical system

Progress in the LAMOST optical system

Configurations for an extremely large telescope with a spherical or aspherical primary mirror