Marília J. Sartori * marilia@iagusp.usp.br

Jane Gregorio-Hetem* jane@iagusp.usp.br

Annibal Hetem Jr. **annibal.hetem@usa.net

(*) UNIVERSIDADE DE SÃO PAULO (IAG/USP)

(**) UNIVERSIDADE PAULISTA (ICET/UNIP)

We have made a statistical study of Herbig Ae/Be stars (HAeBe). The Pico dos Dias Survey, a search for T Tauri stars (TT) based on IRAS colors, has revealed several new TT, as well other very interesting objects, like a hundred of probable new HAeBe.

The strong H_alpha emission, spectral type earlier than F5 and infrared excess similar to TT have been used to classify the candidates. In order to confirm their young nature, we have obtained low-resolution spectra and UBVRI photometry for 54 candidates.

A model to fit the spectral energy distribution (SED) has been used in order to determine stellar parameters, and the contribution of different components in the total emitted flux. In the present work we show the results obtained for 30% of the sample, including some well-known HAeBe to be compared to our candidates.

After a search for massive pre-main sequence (PMS) stars, companions of TT (Herbig 1960), the HAeBe were introduced as a new class of Young Stellar Objects (YSO), based on three basic criteria:

• spectral type earlier than F0,
• spectral features similar to TT (Balmer),
• association with star forming region.

Their PMS nature was confirmed by Strom et al (1972) based on their position on the H-R Diagram, it was found masses and ages in the ranges of 1.5 - 15 solar masses and 10⁵ - 10⁶ yr. 

The spectrophotometric similarities with TT suggest that HAeBe are intermediate mass YSO having an active disk in their circumstellar structure, explaining the observed infrared excess (Hillenbrand et al. 1992).

Conversely to the disk models, other authors have argued that spherical envelope models could reproduce the infrared excess (Hetem et al. 1994, Miroshnichenko et al. 1997).

We observed 54 stars. In the present work we show the first results obtained for a sample of 16 objects.

The spectra were obtained at Pico dos Dias Observatory, by using: 1.6m telescope; Cassegrain Spectrograph; grating 300 l/mm; spectral range 400 – 800 nm.

UBVRI photometry were performed with the 0.6 m telescope, during the Pico dos Dias Survey data acquisition.

Table 1 shows the spectral type (from PDS photometry); the model parameters T_eff and A_V; the fraction of energy emitted by the circumstellar structure. Last column gives notes from literature.

The obtained spectra are showed in Figures 1 to 4, ordered by spectral type: B2 to B9 (Figure 1); A0 (Figure 2); A2 to A5 (Figure 3); A8 to F0 (Figure 4).

We have used our model to fit the SED of our sample, by comparing theoretical curves with the observed spectra and photometry.

The results from the SED fit, are showed in Figures 1 to 16,

The individual contribution on the SED is indicated as the following legend:

Table 1. Stellar parameters of our sample (click on the Fig. number to see the SED)

Notes:

a. Thé et al. (1994) Catalogue: (1) Herbig Ae/Be members and candidates; (4) Emission line stars with IR excess; (6) Supergiant (rejected as HAeBe).

b. Vega-like stars: spectroscopy (Dunkin et al. 1997)

c. Vega like stars: optical, IR, mm (Sylvester et al. 1997)

d. IRAS sources with planetary nebulae colors (Garcia-Lario et al. 1997)

e. Hipparcos photometry (van den Ancker et al. 1998)

f. UV, optical and IR (Malfait et al. 1998)

g. mm continuum mapping (Henning et al. 1998)

h. Polarimetry (Yudin & Evans 1998) i.

i. Beta-Pic type systems: IR photometry (Fajardo-Acosta et al. 1998)

j. Embedded HAeBe (Grady et al. 1998)

k. Protoplanetary nebulae: SiO masers (Nyman et al. 1998)

l. Vega like stars: isophot observations (Heinrichsen & Walker 1998)

• PDS340 (HD100546), PDS398 (HD141569), PDS473 (HD163296), PDS564 (HD179218) were first identified as HAeBe by Thé et al (1994) and more recently they have been deeply studied by Malfait et al. (1998a), specially PDS340, which has been observed by ISO (Malfait et al. 1998b).
• Besides Thé et al (1994) do not consider PDS514 (HD169142) as HAeBe (Oudmaijer et al 1992 have classified it as Be and as binary), this object has been classified by several authors like Vega- or Beta Pic-type star. Yudin & Evans (1998) observed polarimetric variability and evidences of Rayleigh scattering by small grains in the circumstellar envelope.
• PDS307 (csi-57-10198), PDS339 (100453), and PDS451 (irsv1716-3907) have been studied as proto-planetary nebulae. Several authors classify PDS395 (HD139614) as Vega-like star. Considering the differences found between our data and the spectrum presented by Meeus et al. (1998) we suggest that PDS395 shows H_alpha profile variable.

• PDS286, PDS389, and PDS399 are the better examples of HAeBe detected by us. The spectral type, the H_alpha profile and the dust distribution are in good agreement with the expected characteristics of these objects.
• PDS406 and PDS431 are quite similar to PDS307, but they do not show the HeI (5876Å) absorption line, and PDS431 does not show H_alpha emission. Other tests should be made in order to verify if they could be considered as planetary nebula candidates.
• PDS415 is mostly similar to PDS339, in both circumstellar distribution and spectrum features. We noted an emission of H_alpha in the medium-resolution spectrum of PDS415. The fact that H_alpha appears in absorption could be due to a variation of the profile line.
• PDS457 has a SED similar to PDS564. Unless this star has an H_alpha variable, it cannot be considered an HAeBe.