![]() |
(1) |
![]() |
(2) |
This star has a moderate value (230 km s-1). The spectrum shows
double-peaked weak emission inside the photospheric absorption core of the
H
profile. After the photospheric absorption correction, the
equivalent width of the emission component is 1.88
0.05 Å. Value of FWHM
of the emission component, measured through Gaussian profile fitting, is
10.88
0.15 Å. The peak separation between the blue and the red emission
components is 8.8
0.09 Å (
402 km s-1). Computed value of the
emission disk radius is 1.2 times the stellar radius.
In the BSC, this star has been classified as a spectroscopic binary. Due to the
superposition of H profiles of two stars of the binary system may
appear as a
single-peak emission at the absorption core of the line. However, in the case of
HR 1544, the H
profile displays double-peak emission at the core of
this line which is very similar to the H
profiles of classical Be
stars. Also the observed velocity difference between the two absorption cores
is about 505 km s-1 and this value is not consistent with the orbital
parameters. The H
profile (Fig. 2a) shows weak emission at both the
wings that may not be clearly evident. To check this, we have compared the
H
profiles of HR 1544 (A1Vn and
km s-1) and
HR 2155 (A1Vn and
km s-1) and they are shown in Fig. 2b. It can be
clearly seen from the subtracted spectrum (shown on the upper part of Fig. 2b)
that HR 1544 displays emission at H
. Measured parameters of the
H
-emission profile and the computed value of the radius of the
emission disk are presented in Table 2.
The value of this star is given as 160 km s-1 in the BSC. However, we
have measured this value as 355 km s-1, using Eq. (1) and the FWHM
value of the
He I (6678 Å) line of this star. This computed value of
is in good
agreement with that computed using the FWHM value of He I line profile of 5876
Å. The observed velocity difference between the two absorption cores is about
670 km s-1. This value indicates that the weak emission is not due to the
superposition of two absorption line stars. The double-peak emission of
H
separated by a strong absorption component may be due to the shell
absorption. The measured values of
), FWHM,
and the
computed value of
are presented in Table 2.
The revised value of (300 km s-1) of this star is taken from the
remarks part of BSC. Also our computed value of
, using the measured FWHM
value of He I (6678 Å), is in close agreement (
310 km s-1) with
this value. Strong double-peak H
-emission profile is separated by an
absorption component. The radius of the emission disk is almost four times the
radius of this star. Table 2 shows the measured parameters of the emission
profile of H
.
This star is a spectroscopic binary with radial velocity of about -12 km
s-1 (BSC). The rotational velocity of this star is 185 km s-1. The
double-peak emission of H suggest that this emission is not due to
the superposition of two H
absorption profiles of the binary system.
Also the observed velocity difference between the two absorption cores is very
high (
450 km s-1). Even though the emission is weak, but the radius
of the emission disk is almost three times the radius of the star.
The value of this star is not available in the BSC. Also the SIMBAD
database does not contain any information about the
value of this star. We
computed the value of
using the FWHM value of He I ( 6678 Å) profile
and the computed value is 255 km s-1 (Table 2). H
profile of
HR 3878 displays two broad emission components with an central absorption that is
similar to quasi-reversal H
profiles of classical Be stars. From
Table 2 it can be seen that the FWHM value of the H
profile (after
photospheric correction and interpolation) is about 731 km s-1 (16.0 Å).
This indicates that probably the projected rotational velocity of this star may
be larger than that we have computed (
255 km s-1). Future high
resolution line profile of He I(4471 Å) may help to resolve this problem.
HR 4552 is not a Bn/An star. We observed this star as a standard star. The
H profile of this star (Fig. 2a) shows clear double-peaked emission
with strong shell absorption, embedded within the photospheric absorption line.
The
value of HR 4552, given in BSC, is about 72 km s-1. We have also
computed the value of
using the FWHM value of He I line (5876 Å) and our
computed value is close to this value. However, using the FWHM value of the
H
-emission profile, the computed value of
is about 206 km
s-1. We have used this value of
to compute the value of
and it is given in Table 2. The BSC lists this star as a double star and the
second star is separated by 0.8'' with a magnitude difference of
.
It may be possible that the seven newly detected early-type emission-line stars,
mentioned above, might have already been detected as emission-line stars. To
check this, we have searched the SIMBAD database and found that no emissions
have yet been detected in these seven stars. Spectral types of these seven stars
are between B0.5 and A1. However, except one star (HR 3878 - B0.5IIIn) all the
six stars have spectral types of B8 or later. These B and A-type emission-line
stars may be called as Be and Ae stars. Some of these Be and Ae stars may also
be Herbig Ae/Be stars. To find out whether these stars belong to Herbig Ae/Be
stars group or not, we have looked for IRAS (12 , 25
, 60
)
fluxes associated with these seven stars. We have found from the IRAS point
source catalogue (Beichman et al. 1988) that only two stars of these seven
stars, were detected with IRAS (HR 1544 - IRAS 04478+0848 and HR 4552 -
IRAS 11503-3337) and this was also confirmed with the search results of the
SIMBAD database. 12
, 25
and 60
fluxes of HR 1544 and HR 4552 and
another 20 known Be stars were converted into magnitudes using the IRAS
definition for the zero-magnitude. [12] - [25] color versus [12] - [60]
color of Be stars and HR 1544 and HR 4552 were plotted and it has been found from
this plot that HR 1544 and HR 4552 were occupying the same position as that of the
Be stars in this color-color diagram. Also we plotted the (
) color
excess versus temperature of HR 1544 and HR 4552 and compared with the Fig. 4 of
Hillenbrand et al. (1992) and find that these two stars lie in a region where
the Be stars are located and the Herbig Ae/Be stars lie much above the Be stars,
in this diagram. Based on these results we suggest that probably these two stars
do not belong to the Herbig Ae/Be stars group. Also, based on only the
H
profiles and non-detection with IRAS, it is difficult to make any
comment about the Herbig Ae/Be associationship of the rest five stars (HR 1056,
HR 2191, HR 2300, HR 3134 and HR 3878). Presently, we will call these seven newly
detected emission-line stars as Be stars, following the definition of Be stars
(rapidly rotating O, B and A-type stars of luminosity classes III-V with Balmer
emission lines are known as Be stars; details can be seen in
Underhill & Dozan
1982).
Presence of He I line (either 5876 Å or 6678 Å) was detected in all the stars that are listed in Table 2, except HR 1544. It may be interesting to find out whether any of these stars be Bp He-weak or He-strong. This can be checked from the He abundance measurements. High-resolution and high signal-to-noise ratio line profiles of He I (4471 Å) which is a photospheric line, are required to compute the He abundance. With our present data (He I lines of 5876 Å or 6678 Å) it may not be possible to draw any such conclusion.
Close inspection of H-emission profiles of these seven stars
indicates that probably three of these stars may be Be-shell stars (HR 1544,
HR 2191 and HR 4552).
Copyright The European Southern Observatory (ESO)