EUVE_BSL (E0): Extreme UltraViolet Explorer Bright Source List (19950222)
FILES:
euve_bsl.e0 (data file; 356 ultraviolet sources)
euve_bsl.ls (position-list for locating EUVE sources)
CONTENTS: Extreme UltraViolet Explorer (EUVE) Bright Source List
DATASET: These files come in HyperSky dataset E-21, version 19950122 Availability on HyperSky CD-ROM: Vol. 2 (1995)
DESCRIPTION: This datafile contains 356 confirmed extreme ultraviolet (EUV) point souces from the EUVE Bright Source List (BSL), which represents the initial results from the analysis of the EUVE all-sky survey (58-740 Angstroms) and deep survey (67-364 A). The BSL consists of bright EUV point sources detected during the 22 July 1992 to 21 January 1993 survey phase of the EUVE mission, as well as bright sources observed during the in-orbit calibration phase.
The EUVE mission's primary scientific goal was to conduct a photometric survey of the entire sky over the whole EUV band, and to conduct a more sensitive survey along the ecliptic. EUVE was launched on 7 June 1992 and placed into a circular orbit of 550 km altitude at an inclination of 28 degrees.
Over the following six months, two distinct surveys, the all-sky survey and the deep survey, were conducted with the four mission telescopes. The all-sky survey was carried out with four distinct filters that cover the wavelength region 58-740 A. From 22 July 1992 to 21 January 1993, the scanners on three of the telescopes were used to map about 80% of the sky. Concurrently, the fourth telescope, the Deep Survey/Spectrometer was used to carry out the "deep" survey (more sensitive by a factor of ten) of a 2 deg by 180 deg strip of the sky along the ecliptic in two filters covering the wavelength region 67-364 Angstroms.
The resulting BSL is not meant to be complete; rather it is the first release of the sources bright enough that their existence as EUV sources is not in doubt. For 341 sources, the BSL includes optical identifications and associated visual magnitudes. Fifteen EUV sources do not have yet any plausible optical counterpart. The two largest source classes detected at the EUV wavelength are late-type stars and white dwarf stars.
The HyperSky file is based on a version of the EUVE BSL available at the following World Wide Web site (as of February 1995):
http://www.cea.berkeley.edu/Archive/Survey/about_survey.html
Also available at this site is additional documentation which more fully describes the EUVE project and results.
DATA:
The HyperSky datafile contains the following data from the BSL:
POSITION: Right Ascension and Declination are taken from the BSL's equinox 2000 positions. BSL positions were provided to an accuracy of 1 second in Right Ascension and 1' in declination.
MAG: Visual magnitudes were provided for optical candidates for each source, and are given in the comments (see below). However, those magnitudes are not related to EUV source intensities. Consequently, a set of artificial HyperSky EUV "magnitudes" is provided strictly to allow use of HyperSky's limiting-magnitude controls. In this way, users can display only those sources above a desired threshold. The artificial magnitude system is based on the relation (from Pogson) used to define visual magnitudes:
m1 - m2 = 2.5 * log10(S1/S2)
where { m1, m2 } are magnitudes, and { S1, S2 } are source count rates from the EUVE Lexan/B scanner filter, as discussed in the comments below. For the HyperSky catalog, the brightest source (S1 = 29370 count rate) is arbitrarily assigned the magnitude m1 = 1.0. Given this, any other source S2 can have its relative magnitude, m2, derived using the relation:
m2 = 1.0 + 2.5 * log10 (29370/S2);
In this system, the faintest BSL source (count rate 4) has a magnitude of 10.7. The following table summarizes the relation between magnitude and count rate for catalog extremes and intermediate magnitudes:
Magnitude Source Count Rate (Lexan/B)
----------|----------------------------
1.0 29370 (strongest BSL source count)
2.6 6590
3.7 2500
4.6 1060
5.5 460
6.5 180
7.6 70
8.5 30
9.7 10
10.7 4 (weakest BSL source count)
Using the above table, you can set HyperSky's limiting magnitude (for emission sources) to mask out BSL sources below a desired count rate. Except for this use, the derived source magnitudes have NO significance. It should be emphasized again that the magnitudes are NOT provided in the BSL; only the count rates are fundamental BSL values.
IDENTIFICATION: The EUVE source name as specified by the International Astronomical Union. Each source is identified by its J2000 coordinates in hours and minutes of RA (Right Ascension) and decimal degrees of declination.
COMMENTS: The comment line contains the following information, provided if available for each EUVE source:
* A line starting with "count=", giving the count rate, in counts per kilosecond, for the source in the scanner's Lexan/B filter. Lexan/B filter counts are provided in the HyperSky file (instead of counts from the other 3 filters) because the BSL provides count rates for many more sources from the Lexan/B filter than the other filters. Lexan/B count rates range from a high of 29370 to a recorded low of 4. Some sources for which the BSL provides only non-Lexan/B counts do not show count rates in the HyperSky file.
* The line "Optical candidate:", if such an object has been identified for the EUV source.
* The name (and possibly a second alternate name) for the optical counterpart candidate identified for the EUV source. Candidates came from a detailed of astronomical catalogs of astronomical catalogs, including the SIMBAD and NED databases, for sources most likely to emit EUV radiation. Such sources include white white dwarf (WD) stars, active late-type stars, cataclysmic variables, and active extragalactic objects in directions having low hydrogen column density. All identified counterparts lie within 1.5 arc minutes of the EUVE source position, except for the deep survey, where the most likely candidate within 3 arc minutes is listed.
* The visual magnitude of the optical counterpart, in parentheses following the above names.
* A line giving the source type or spectral type of the optical candidate for the EUV source. Spectral types generally come from the SIMBAD database and follow the SIMBAD spectral type coding. Extragalactic source types are from NED (the NASA Extragalactic Database).
POSITION-LIST: The position-list euve_bsl.ls, if loaded, enables you to locate an EUV source position using either of two sublists:
* A list ordered by Right Ascension.
* A list in order of decreasing Lexan/B count rate, putting the most intense sources at the top of the position list.
In addition to source positions, each list also shows source count rates ("c=") and the names of the optical counterparts, if known, and their associated visual magnitudes in parentheses.
Remember that this is only a position-list; it does not actually display a souce at the position you select. The source you select will appear at the position only if you have also loaded euve_bsl.e0, or some other HyperSky catalog file which contains the source.
REFERENCES See the URL documentation cited above.