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J/ApJS/99/135 Rotation and Spectral Peculiarities (Abt+ 1995)
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The Relation Between Rotational Velocities and Spectral Peculiarities
Among A-Type Stars
Abt H.A., Morrell N.I.
<Astrophys. J. Suppl. Ser. 99, 135 (1995)>
=1995ApJS...99..135A
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ADC_Keywords: Rotational velocities ; Equivalent widths ; Stars, peculiar
Keywords: stars: chemically peculiar -- stars: early-type --
stars: fundamental parameters -- stars: rotation
Abstract:
We obtained new data to determine whether the spectral appearance of
A-type stars is entirely determined by their rotational velocities.
For this purpose we derived rotational velocities for 1700 northern
A-type stars from CCD coude spectra, calibrated with the new Slettebak
et al. system, and new MK classifications based on wide photographic
Cassegrain spectra for 2000 northern and some southern stars in the
Bright Star Catalogue. In addition we determined the equivalent widths
of the lambda 4481 Mg II lines in the coude spectra. Tables and graphs
show variations of rotational velocities and lambda 4481 line
strengths as functions of type and luminosity, and frequencies of the
normal and abnormal stars.
After deconvolutions of the rotational velocities, assuming random
orientations of rotational axes, we find that all rapid rotators have
normal spectra and nearly all slow rotators have abnormal spectra (Ap
or Am). Those abnormalities are generally attributed to diffusion and
can occur only with little rotational mixing. However at all types
there are overlaps of these distributions, implying that a given
intermediate rotational velocity is insufficient to determine whether
the star should have a normal or abnormal spectrum. However, we
realized that (1) some of our "standards," such as Vega and Alpha Dra,
are really abnormal, causing us to classify similar peculiar stars as
"normal," (2) many of the "normal" stars near A2 IV have the
characteristics of peculiar stars such as low rotational velocities
and weak 4481 Mg II and K lines, and (3) the mean rotational
velocities of "normal" stars are depressed just at those types where
the Ap and Am stars are most frequent. Therefore we conclude that the
overlaps are due to our failure to detect all the abnormal stars and
that a specific rotational velocity is probably enough to determine
whether a star will have a normal or abnormal spectrum.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 57 2092 Summary of Stellar Data
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- HR *Bright Star Catalogue number
7-15 A9 --- HD *Henry Draper or Aitken Double Star number
17-44 A28 --- MK *MK classification
45 A1 --- l_Vsini Limiting character on Vsini
46-48 I3 km/s Vsini []? Vsini, rotational velocity
49-50 A2 --- u_Vsini *[:?pst ] Vsini uncertainty flag
53-56 F4.2 0.1nm W4481 []? Equivalent width for 4481 A line
57 A1 --- u_W4481 *[:pst] W4481 uncertainty flag
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Note on HR, HD:
If both the HR and HD fields are blank, the remaining fields are
continuations of the previous record.
Note on MK:
Explanation of the Classification Terminology (from Table 1):
(standard) Classification standard star
s Sharp lined
n Broad lined
nn Very broad lined
ksn The Ca II K line has both sharp and broad components
st Strong
wk Weak
v. Very
Lam Boo A star in which many of the metals are weak,
indicating underabundances
4481 weak The 4481 Mg II line is weak. Measures may
indicate that other lines are also weak.
This may be a mild version of the Lambda
Boo stars.
Am(A3/A7/F0) A metallic line star in which the spectral
type based on the Ca II K line is A3, on the
Balmer lines is A7, and on the metallic
lines is F0. This is an abbreviation of the
form Am(K/H/M=A3/A7/F0).
p(SrEuCr st, CaMg wk) An Ap star in which the Sr is strongest
relative to the standards, Eu is next
strongest, etc.; the lines of Ca and Mg are
weak relative to those in standards. The
type is based on the hydrogen lines.
shell(Ti,Ca) A shell spectrum that has sharp Ti and Ca
absorption lines.
(:) Uncertainty in the previous symbol.
Note on u_Vsini, u_W4481:
Uncertainty flag, or indication if this is a program star (p) or
a star from Slettebak et al. (1975ApJS...29..137S)
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Origin: AAS CD-ROM series, Volume 5, 1995 Lee Brotzman [ADS] 02-Aug-95
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(End) [CDS] 01-Feb-1996