The Dachs photometric system
Basic Reference
Dachs J., Schmidt-Kaler Th. 1975, A&AS 21, 81
Abstract
100 bright equatorial and southern stars of spectral type O, B, A, F, to G0
and of luminosity classes I through V have been measured with a photoelectric
photometer equipped with two interference filters of 13 Å and 157
Å bandwidth centered on Halpha.
The stars are evenly distributed in right ascension and
intended to provide a standard system of Halpha line photometry. The
observing technique and the method used in establishing the standard system
are described. The resulting photometric indices alpha of the Halpha line
strength are compiled in table 3. They are compared with the equivalent
widths of Halpha known for 25 programme stars. With Crawford's beta index
of the strength of the Hbeta line for 94 stars in common with Crawford's
lists. With Feinstein's photoelectric Halpha indices measured with
a pair of interference filters of 54 Å and 159 Å bandwidth,
and with the spectrophotometric Ralpha index of Halpha line
strength measured by Andrews for 36 of our programme stars. The
advantage of using an interference filter of very small half-bandwidth in
photoelectric Halpha line photometry is emphasized.
Principal objectives of the alpha system are: (1) The value of alpha is an
excellent luminosity criterion especially for early-type supergiants and
heavily reddened OB type stars of spectral type later than about O9. (2)
By measuring simultaneously the alpha and beta indices for OB type stars it
is possible to discriminate between emission-line stars of low luminosity
and non-emission stars of high luminosity of the same spectral type. (3)
Stars with variable hydrogen-line emission and peculiarities in their spectra
may be identified from their location in the alpha - beta diagram which
deviates from the mean relation for normal stars.
Several stars with variable strength of alpha emission are noted. The shell
event which occured in dzeta Oph between 1971 and 1973 is also found in our
observations.
Content
Access to the data and references
Asiago Database on Photometric System (ADPS)
Indices and Parameters
alpha
Filters
Peak
Filter wavelength Width Name
[Å] [Å]
Narrow 6560.5 13 Baird Atomic B11(X)
Wide 6566. 157 Baird Atomic B2
Photomultiplier
EMI 9558A
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Last update: 21 May 1996