3 Results and discussion

Spectra of 33 Bn, 49 An and 24 B and A stars were analyzed. It has been found from the spectra of 82 Bn and An stars that seven stars displayed the presence of emission in their H$_\alpha$. These are the new emission-line Bn and An stars. Also we have independently detected H$_\alpha$-emission in two more Bn and An stars (Fig. 1) that were earlier reported as emission-line stars (HR 1037, Cote & van Kerwijk 1993 and HR 2244, Irvine 1990). Comparison of Fig. 3 of Cote & van Kerwijk (1993) and Fig. 1 of the present paper, clearly shows that the H$_\alpha$-emission strength of HR 1037 decreased between August 1990 and January 1997. However, the H$_\alpha$-emission strength of HR 2244 increased considerably since Irvine's detection (from the comparison of Fig. 1 of the present paper and Fig. 3 of Irvine 1993). Observed H$_\alpha$-emission profiles of seven new Be stars (four Bne and three Ane stars) are shown in Figs. 2a-c. Figure 2a shows the H$_\alpha$emission profiles of HR 1544 and HR 4552 that were observed using the Coudé Echelle spectrograph. It appears from this figure that the emission in H$_\alpha$ profile may be doubtful. To check this we also obtained the spectrum of HR 2155 that has similar spectral type, luminosity class and rotational velocity as that of HR 1544. Lower part of Fig. 2b presents superimposed H$_\alpha$ profiles of HR 1544 (A1Vn and $v\sin i =212$km s^-1) and HR 2155 (A1Vn and $v\sin i =211$ km s^-1). From the comparison of these two profiles, it may be seen that HR 1544 is an emission-line star (subtracted spectrum is presented in the upper part of Fig. 2b). Cassegrain spectra of five new Be stars are shown in Fig. 2c. We have computed the projected rotational velocities ($v\sin i$) of three Bn and An stars, using the full width at half intensity maximum (FWHM) values of He I lines (5876 Å and 6678 Å) where the He I lines have been assumed to be Gaussian profiles. Under this assumption the $v\sin i$ values were computed using the following formula (Buscombe 1969):

$$\frac{v\sin i}{c}=\frac{FWHM}{2\lambda_{0}(\ln 2)^{1/2}}$$ (1)

where $\lambda_{0}$ is the laboratory wavelength and c is the velocity of light. The $v\sin i$ values of other four Bn and An stars were obtained from the Bright Star Catalogue (Hoffleit & Jaschek 1982). Measured equivalent widths [$W(\alpha$)], FWHM (instrumental broadening corrected) and the peak separations ($\Delta V_{\rm peak}$) of seven new Be stars are given in Table 2, along with the $v\sin i$ values. We have also computed the radii of the emission disk of the Be stars, using the following equation (Huang 1972):

$$\frac{R_{\rm e}}{R_{*}}=(\frac{2 v\sin i}{\Delta V_{\rm peak}})^{1/j}$$ (2)

where $R_{\rm e}$ is the radius of the emission-disk and R_* is the photospheric radius and j is an exponent that characterizes the rotation law (j=0.5 for Keplerian rotation of the disk and j=1.0 for rotation with conservation of angular momentum). To compute the values of $R_{\rm e}$/R_*, we have used j=0.5. Computed values of $R_{\rm e}/R_{*}$ of the new Be stars are given in the last column of Table 2. Errors in $W(\alpha$) measurements were computed using the expression of $\sigma[W(\alpha$)] given in Ghosh (1988) and Ghosh et al. (1990) and the errors in FWHM, $\Delta V_{\rm peak}$, $R_{\rm e}/R_{*}$ were computed using the errors of wavelength calibration. Brief discussion about the seven new Be stars is given below:

  

Table 1: List of observed An/Bn stars

  

Table 2: The new Be stars

HR 1056, HD 21620 (A0Vn)

This star has a moderate $v\sin i$ value (230 km s^-1). The spectrum shows double-peaked weak emission inside the photospheric absorption core of the H$_\alpha$ profile. After the photospheric absorption correction, the equivalent width of the emission component is 1.88 $\pm$ 0.05 Å. Value of FWHM of the emission component, measured through Gaussian profile fitting, is 10.88 $\pm$ 0.15 Å. The peak separation between the blue and the red emission components is 8.8 $\pm$ 0.09 Å ($\sim$402 km s^-1). Computed value of the emission disk radius is 1.2 times the stellar radius.

HR 1544, HD 30739 (A1Vn)

In the BSC, this star has been classified as a spectroscopic binary. Due to the superposition of H$_\alpha$ 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$_\alpha$ profile displays double-peak emission at the core of this line which is very similar to the H$_\alpha$ 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$_\alpha$ profile (Fig. 2a) shows weak emission at both the wings that may not be clearly evident. To check this, we have compared the H$_\alpha$ profiles of HR 1544 (A1Vn and $v\sin i =212$ km s^-1) and HR 2155 (A1Vn and $v\sin i =211$ 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$_\alpha$. Measured parameters of the H$_\alpha$-emission profile and the computed value of the radius of the emission disk are presented in Table 2.

HR 2191, HD 42477 (A0Vnn)

The $v\sin i$ 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 $v\sin i$ 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$_\alpha$ separated by a strong absorption component may be due to the shell absorption. The measured values of $W(\alpha$), FWHM, $\Delta V_{\rm peak}$ and the computed value of $R_{\rm e}/R_{*}$ are presented in Table 2.

HR 2300, HD 44783 (B8Vn)

The revised value of $v\sin i$ (300 km s^-1) of this star is taken from the remarks part of BSC. Also our computed value of $v\sin i$, using the measured FWHM value of He I (6678 Å), is in close agreement ($\sim$310 km s^-1) with this value. Strong double-peak H$_\alpha$-emission profile is separated by an absorption component. The radius of the emission disk is almost four times the radius of this star. Table 2 shows the measured parameters of the emission profile of H$_\alpha$.

HR 3134, HD 65873 (B9.5 Vn)

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$_\alpha$ suggest that this emission is not due to the superposition of two H$_\alpha$ absorption profiles of the binary system. Also the observed velocity difference between the two absorption cores is very high ($\sim$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.

HR 3878, HD 84567 (B0.5 IIIn)

The $v\sin i$ value of this star is not available in the BSC. Also the SIMBAD database does not contain any information about the $v\sin i$ value of this star. We computed the value of $v\sin i$ using the FWHM value of He I ( 6678 Å) profile and the computed value is 255 km s^-1 (Table 2). H$_\alpha$ profile of HR 3878 displays two broad emission components with an central absorption that is similar to quasi-reversal H$_\alpha$ profiles of classical Be stars. From Table 2 it can be seen that the FWHM value of the H$_\alpha$ 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 ($v\sin i$ $\sim$ 255 km s^-1). Future high resolution line profile of He I(4471 Å) may help to resolve this problem.

HR 4552, HD 103192 (B9IIIpSi)

HR 4552 is not a Bn/An star. We observed this star as a standard star. The H$_\alpha$ profile of this star (Fig. 2a) shows clear double-peaked emission with strong shell absorption, embedded within the photospheric absorption line. The $v\sin i$ value of HR 4552, given in BSC, is about 72 km s^-1. We have also computed the value of $v\sin i$ 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$_\alpha$-emission profile, the computed value of $v\sin i$ is about 206 km s^-1. We have used this value of $v\sin i$ to compute the value of $R_{\rm e}/R_{*}$ 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 $0\hbox{$.\!\!^{\rm m}$}9$.

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 $\mu$, 25 $\mu$, 60 $\mu$) 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 $\mu$, 25 $\mu$ and 60 $\mu$ 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 ($V-12~\mu$) 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$_\alpha$ 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$_\alpha$-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).