Information on Service 'DFBS spectra preview maker'

The First Byurakan Survey (FBS) is the largest and the first systematic objective prism survey of the extragalactic sky. It covers 17,000 sq.deg. in the Northern sky together with a high galactic latitudes region in the Southern sky. The FBS has been carried out by B.E. Markarian, V.A. Lipovetski and J.A. Stepanian in 1965-1980 with the Byurakan Observatory 102/132/213 cm (40"/52"/84") Schmidt telescope using 1.5 deg. prism. Each FBS plate contains low-dispersion spectra of some 15,000-20,000 objects; the whole survey consists of about 20,000,000 objects.

For a list of all services and tables belonging to this service's resource, see Information on resource 'Digitized First Byurakan Survey (DFBS) Extracted Spectra'

Service Documentation

Usage Hints

Note that the spectra are not flux calibrated. Indeed, they were scanned off of different emulsions, and only spectra from compatible emulsions should be compared. The following emulsions occur in the database:

n emulsion
334409 103aF
18695 103aO
3622 IF
13555 IIAD
2409058 IIAF
16545 IIAF bkd
3254370 IIF
313287 IIF bkd
7871 IIIAJ bkd
6645 IIIF
18967 IIIaF
8122 IIaD
3565737 IIaF
6735 IIaO
16755 OAF
8794 ORWO CP-3
8097 ZP-3
23702 Zu-2

Upper- and lowercase versions of the emulsions are actually different (e.g., IIAD was produced in England, IIaD in the US). Their properties are different enough to make mixing spectra for the different emulsions unwise.

Also note the sp_class column. Unless you take great precaution, you probably should only use spectra with sp_class='OK'.

Spectra can be retrieved in VOTable form (via SSA or the accref field from the TAP table), but it will usually be faster to directly pull them from the spectral and flux arrays.

Actually, array indices in the flux arrays correspond to fixed wavelengths. In other words, the spectral column is constant in the database.

The flux arrays are actually of different length. The always start at index 1, corresponding to 690 nm. The blue end depends on how far some signal was suspected.

Use Cases

Locate Spectra by Features

While ADQL support for array operations is rather weak, you can subscript arrays. Because of the fixed bins, you can therefore select by flux ratios (never use absolute numbers here; they are meaningless). For instance, to select objects with a high (apparent) Halpha emission (656 nm, corresponding to array index 3), you might so something like:

select * from dfbsspec.spectra
where
  flux[3]/(flux[40]+flux[41]+flux[42])>30
  and sp_class='OK'

Since the table needs to be sequentially scanned for this, it will take a minute or so. Combine with an object selection (see below) or other criteria if possible.

Get Average Spectra

You cannot currently use the ADQL aggregate function AVG with arrays (which should be fixed at some time in the future). Meanwhile, you can work around this with a clumsy construction like this (this query will give you average spectra by magnitude bin; don't run it just for fun, it'll take a while):

select round(magb) as bin, avg(flux[1]) as col1, avg(flux[2]) as col2,
  avg(flux[3]) as col3, avg(flux[4]) as col4, avg(flux[5]) as col5,
  avg(flux[6]) as col6, avg(flux[7]) as col7, avg(flux[8]) as col8,
  avg(flux[9]) as col9, avg(flux[10]) as col10, avg(flux[11]) as col11,
  avg(flux[12]) as col12, avg(flux[13]) as col13, avg(flux[14]) as col14,
  avg(flux[15]) as col15, avg(flux[16]) as col16, avg(flux[17]) as col17,
  avg(flux[18]) as col18, avg(flux[19]) as col19, avg(flux[20]) as col20,
  avg(flux[21]) as col21, avg(flux[22]) as col22, avg(flux[23]) as col23,
  avg(flux[24]) as col24, avg(flux[25]) as col25, avg(flux[26]) as col26,
  avg(flux[27]) as col27, avg(flux[28]) as col28, avg(flux[29]) as col29,
  avg(flux[30]) as col30, avg(flux[31]) as col31, avg(flux[32]) as col32,
  avg(flux[33]) as col33, avg(flux[34]) as col34, avg(flux[35]) as col35,
  avg(flux[36]) as col36, avg(flux[37]) as col37, avg(flux[38]) as col38,
  avg(flux[39]) as col39, avg(flux[40]) as col40, avg(flux[41]) as col41,
  avg(flux[42]) as col42, avg(flux[43]) as col43, avg(flux[44]) as col44,
  avg(flux[45]) as col45, avg(flux[46]) as col46, avg(flux[47]) as col47,
  avg(flux[48]) as col48, avg(flux[49]) as col49, avg(flux[50]) as col50,
  avg(flux[51]) as col51, avg(flux[52]) as col52, avg(flux[53]) as col53,
  avg(flux[54]) as col54, avg(flux[55]) as col55, avg(flux[56]) as col56,
  avg(flux[57]) as col57, avg(flux[58]) as col58, avg(flux[59]) as col59
from dfbsspec.spectra
where sp_class='OK'
group by bin

To map col<n> to wavelenghts, see the contents of (any) spectral column.

Build Templates

To compute an average spectrum for a class of objects, we suggest to pull positions of such objects from SIMBAD and then fetch the associate spectra from this database. Since the response function of the photographic plates had a strong magnitude dependence, restrict the objects to a small magnitude range, for instance:

select
    otype, ra, dec, flux
from basic
join flux
on (oid=oidref)
where
    otype='HS*'
    and dec>-15
    and filter='G'
    and flux between 12.5 and 13.5

(to be executed on SIMBAD's TAP service, see also SIMBAD object types).

With the resulting table, go do this service and execute a query like:

SELECT
specid, spectral, flux
FROM dfbsspec.spectra AS db
JOIN TAP_UPLOAD.t1 AS tc
ON DISTANCE(tc.ra, tc.dec, db.ra, db.dec)<5./3600.
WHERE sp_class='OK'

(adjust t1 according to your client's rules; in TOPCAT, that's t plus the table number from the control window).

History of this Data Collection

The original aim of the First Byurakan Survey was to search for galaxies with UV excess (1986ApJS...62..751M, Markarian et al. 1989,1997- catalogue No. VII/172 at CDS). Successively, the amount of spectral information contained in the plates allowed the development of several other projects concerning the spectral classification of Seyfert Galaxies (Weedman and Kachikian 1971), the first definition of starburst galaxies (Weedman 1977 ), the discovery and investigation of blue stellar objects (Abrahamian and Mickaelian, 1996, Mickaelian et al 2001, 2002, CDS catalogue No II/223) and a survey for late-type stars (Gigoyan et al. 2002). All these results were obtained by eye inspection of the plates performed with the aid of a microscope at the Byurakan Observatory. The number and classes of new objects discovered FBS made clear the need of open access to FBS for the entire astronomical community.

Overview

You can access this service using:

This service is not published. This can mean that it was deemed too unimportant, for internal use only, or is just a helper for a published service. Equally likely, however, it is under development, abandoned in development or otherwise unfinished. Exercise caution.

Other services provided on the underlying data include:

Spatial Coverage

Input Fields

The following fields are available to provide input to the service (with some renderers, some of these fields may be unavailable):

NameTable Head DescriptionUnitUCD
specid Specid ID of the spectrum to produce a preview for N/A N/A

VOResource XML (that's something exclusively for VO nerds)