LAMOST DR7 Frequently Asked Questions

About the LAMOST Spectral Survey

1. What is the LAMOST Spectral Survey?

LAMOST spectral survey contains two main parts: the LAMOST ExtraGAlactic Survey (LEGAS), and the LAMOST Experiment for Galactic Understanding and Exploration (LEGUE) survey of Milky Way stellar structure. The unique design of LAMOST enables it to take 4000 spectra in a single exposure.

LAMOST has been renamed as ‘Guo Shou Jing Telescope’ in 2010, Guo Shou Jing was a Chinese astronomer, engineer, and mathematician who lived during the Yuan Dynasty (1271–1368).

2. What data does LAMOST DR7 release?

LAMOST DR7 totally releases xxx spectra, include xxx objects of the pilot survey (2011-10-24~2012-06-30), xxx objects of the first-year regular survey (2012-09-28~2013-06-30), xxx objects of the second-year regular survey (2013-09-10~2014-06-30), and xxx objects of the third year regular survey (2014-09-xx~2015-06-xx).
Similar as DR1 and dr7, DR7 also includes two types of data: optical spectra (flux- and wavelength-calibrated, sky-subtracted), and catalog data, which includes both parameters measure from spectra, such as redshifts and signal to noise ratios, and parameters inherited from input catalogs. You should keep in mind that LAMOST is a spectral survey telescope, and the parameters related to photometry, which you get here, all come from other surveys.

3. What help is available for DR7?

If you have a question about the nature of the data, consult the Data Description page.

Frequently Asked Questions (FAQ) in this page provides answers to common questions about the LAMOST DR7, and our data access tools.

Query Introduction tells you not only how to search for information you want but also what the tools mean.

To know more about Structured Query Language (SQL), consult the SQL samples or go to the home of MYSQL.

4. What is the sky coverage of DR7? Where in the sky do DR7 data come from?

This page shows what areas of sky (sky coverage) are included in LAMOST DR7.

5. How can I search for data?

When you search for data in LAMOST DR7, you are going through the LAMOST DR7 database and looking for objects that match criteria you choose. For simple searches of spectra, use catalog search and the Query Introduction. For more complex searches, use SQL.

6. How can I match a list of objects to see what data are available for them in DR7?

If you have a fairly small list of objects to match - a few hundred or so - use the catalog search tool. Paste your list of objects, or upload a file containing 3 columns of ra,dec,radius in format Query Introduction tells you. Click Search. The next page will show only those objects that appear in the LAMOST DR7.

About DR7 data

1. How can I read the wavelengths of FITS files?

The format of LAMOST DR7 FITS files are similar as SDSS FITS files. You can get the wavelengths of FITS files through reading the FITS header. Totally, there are three keywords related to wavelength: NAXIS1, COEFF0, and COEFF1. The NAXIS1 keyword represents the number of wavelength array, the COEFF0 keyword represents the central wavelength (log10) of first pixel, and the COEFF1 keyword represents the dispersion (log10) between every two pixels. You should be careful that both COEFF0 and COEFF1 are given in log10-scale.

2. How do I view individual spectrum files in IRAF?

The IRAF package has been traditionally used in astronomy. For LAMOST DR7 data, the splot task can be used to view individual spectrum files. However, splot only understands spectrum files formatted in a specific way. In LAMOST DR7, spec files were formatted in a manner consistent with splot.

3. How do I read catalogs in format of FITS?

Catalog data summarize quantities measured from the spectra such as redshifts, signal to noise ratios, and object classifications. These are available either from the Catalog Search database, or as binary tables in FITS and CSV file formats.You can find them here, and read them by any common FITS-read softwares.

4. What are the differences between the general catalog and catalogs of A, M ,and AFGK?

The catalogs of ‘A F G K’ type stars, ‘A’ type stars, and ’M’ type stars are all subsets of the LAMOST general catalog, you can find the details here.

5. What do magtype and mag1 to mag7 mean? (How can I get the magnitude I need?)

The targets of LAMOST DR1 are provided by different astronomers, and they are from various photometric catalogs, e.g. SDSS, 2MASS, NVSS, Kepler, etc. Thus, magtype follows and reflects the variety of targets selection.

You can search for the magnitudes according to magtype. For example, if you set magtype as ‘ugrizjh’, then you get ‘mag1’ as magnitude in SDSS u-band, ‘mag2’ as magnitude in g-band, ‘mag3’ as magnitude in r-band, ‘mag4’ as magnitude in i-band, ‘mag5’ as magnitude in z-band, ‘mag6’ as magnitude in j-band, and ‘mag7’ as magnitude in h-band. Besides, if you set magtype as ‘griz’, then you get ‘mag1’ as magnitude in g-band, ‘mag2’ as magnitude in r-band, ‘mag3’ as magnitude in i-band, ‘mag4’ as magnitude in z-band, and ‘mag5’, ‘mag6’, ‘mag7’ all as NULL.

6. Why can`t I plot spectrum in “View Spectrum” page?

The View Spectrum page requires that your browser supports HTML5. Please use the latest version of browsers. In our tests, Chrome, Safari, Firefox and Internet Explorer could work.

7. Why can`t I use Specview or Aladin?

1) Please install Java Runtime Environment.

2) The specview is self-signed, please add to your Java Exception SiteList.