We did not find any optical counterpart in either the prints of the Sky Survey for IRAS sources 02408+5458, 06403-0138 and 12384-4536. We found an optical counterpart for IRAS sources 04179+4145, 04278+2253, 06426-0825, 06510+1200 and 07593-1452 on only the POSS R prints. In the case of IRAS 07430+1115 the optical counterpart is found to be on the edge of the IRAS error ellipse. Our finding charts do not show the optical counterpart of the IRAS source 09032-3953, although an extremely faint one appears on the ESO/SERC print (due to difficulties in copying these survey prints which are enclosed in plastic sheets). We group sources occuring in the same region of the VH diagram together and then discuss selected sources in the order of their increasing serial number in each region. For some of the sources we have shown in Fig. 3 (click here) flux distribution curves based on optical near IR and IRAS data.
IRAS 04184+2008, IRAS 06462-0825, IRAS 06510+1200, IRAS 07593-1452, IRAS 14512-4746, IRAS 18599-2246 are in the region I of VH diagram (Fig. 2 (click here)). The sources in this region are mostly due to the radiation from the photospheres. There is very little contribution to the IRAS fluxes from the circumstellar dust around these stars. The IRAS data does not indicate for the presence of dust envelopes around these stars. # 5 IRAS 04184+2008 We have carried out BVRI photometric observations of this source on three different nights viz., 920124, 921226 and 941229. The star is found to be brighter by about 2.5 magnitudes in V at epochs 920124 and 921226 compared to that at epoch 941229. It thus appears to be variable at the optical wavelengths also. Its position in the V-I versus B-V colour-colour diagram (Fig. 1 (click here)) indicates it to be a star of spectral type M5 or later. Stephenson (1986), assigns a spectral type M6 and from an examination of its spectrum in the 5000-6800 Å region obtained at a dispersion of about at . # 16 IRAS 06510+1200 The large differences in the VRI data at the two epochs of our observation suggest that it is variable at the optical wavelengths even though its IRAS variability index indicates that it is unlikely to be a variable at the far-infrared wavelengths. Its IRAS [12-25] and [25-60] colours and LRS spectrum indicate it to be either a `Bright star' or a carbon-rich star. The position of this star in the V-I versus B-V colour-colour diagram (see Fig. 1 (click here)) shows that it is highly reddened and that a significant fraction of its reddening is perhaps due to circumstellar dust. # 26 IRAS 14512-4746 (CD -47 9519) The B-V value indicates it to be a star of spectral type G8Ia, or K0III or K4V. Its [12-25] and [25-60] colours and LRS spectrum indicate it to be an oxygen rich star. It is identified with CD-47 9519 , with B and V magnitudes of 11.1 and 9.3 respectively, and a spectral type M5III (Simbad database).
Figure 3: The flux distribution of some of the sources listed in Table 1
IRAS 17201-4613, IRAS 17318-3606 are in the region II of VH diagram (Fig. 2 (click here)). Sources in this region have thin oxygen rich circumstellar envelopes. IRAS 17201-4613 is identified with HD 157144 (V =9.2, B =10.9, M6III).
Sources in the region IIIa of VH diagram (Fig. 2 (click here)) are characterized by moderately-thick oxygen rich circumstellar envelopes. Sources in the region IIIb show thick oxygen rich circumstellar envelopes and sources in region IV are characterized by very thick oxygen thick circumstellar envelopes. According to the definition of van der Veen & Habing (1988), most cold AGB circumstellar envelopes are in regions IV, IIIb and coldest part of IIIa and protoplanetary nebulae are in region V. Among the circumstellar envelopes, the coldest ones are: i) AGB circumstellar envelopes with large mass-loss rates which are optically thick in the near infrared and emitting most of their energy in the far infrared. These are most likely to be the (very cold AGB, OH/IR stars and very cold carbon rich AGB stars) very late stages of the AGB with a large initial mass., ii) detached circumstellar envelopes associated with stars of intermediate spectral types believed to be in post-AGB stage or probably proto-planetary nebulae (Parthasarathy & Pottasch 1986). Again, they can be oxygen rich or carbon rich, with various mass-loss rates.
The sources described below which are in regions IIIa, IIIb, IV and V are most likely very cold AGB OH/IR stars, or very cold carbon rich AGB stars and post-AGB stars. # 23 IRAS 12384-4536 We did not find any optical counterpart for this source in the Sky Survey prints. It was detected in the OH(1612 MHz) line by Lintel Hekkert et al. (1991), and was found to have a standard two peak spectrum with a velocity width of and a mean of with flux densities of 4.50 mJy and 4.32 mJy for the blue and red shifted spikes. Nyman et al. (1992) carried out CO(J=1-0) observations of this source and detected it. They found it to have an expansion velocity of and an of . Fouque et al. (1992), carried out near infrared photometric observations of this source and detected it in the JHKLM bands. Its expansion velocity indicates that it is an AGB star undergoing mass loss. The LRS spectrum indicates that it is an oxygen rich circumstellar envelope. The flux distribution is shown in Fig. 3 (click here).
# 24 IRAS 12387-3717 Fouque et al. (1992) have carried out near infrared photometric observations of this source and obtain JHKLM magnitudes. It is seen from a combination of our data with that of Fouque et al. (1992), that it has a V-K of and hence highly obscured. It is perhaps also a variable at the optical wavelengths. The flux distribution is shown in Fig. 3 (click here). # 29 IRAS 17174-4641 The LRS spectrum indicates that it is an oxygen rich circumstellar envelope. Nyman et al. (1992) could not detect CO(J=1-0) emission. # 32 IRAS 18123+0511 This source has been detected in the OH(1612 MHz) line by Eder et al. (1988). Lawrence et al. (1990) have carried out infrared photometric observations of this source in the wavelength range , and give JHKLMN magnitudes. They also list magnitudes of this source in a number of narrow bands around the silicate feature and at . The flux distribution is shown in Fig. 3 (click here).
# 2 IRAS 02408+5458 Blommaert et al. (1993) observed this source in the infrared in K, , , , , and Q bands and obtained magnitudes and classified it as a carbon star. The flux distribution is shown in Fig. 3 (click here). # 8 IRAS 04386+5722 Blommaert et al. (1993) carried out near infrared photometric observations of this source. Its position in B-V vs. V-I is shown in Fig. 1 (click here). # 14 IRAS 06403-0138 Photometric observations of this source in the JHKLM bands were carried out by Blommaert et al. (1993). The flux distribution is shown in Fig. 3 (click here). # 25 IRAS 14429-4539 This source is most likely a post-AGB star. Both Fouque et al. (1992), and Hu et al. (1993), report JHKLM magnitudes of this source which are in very good agreement with one another. Optical data in combination with near-infrared photometric data yields a V-K of 4.5 suggesting that it may be highly obscured object. Its flux distribution is shown in Fig. 3 (click here).
IRAS 04101+3103, IRAS 05089+0459, IRAS 05245+0022, IRAS 08005-2356 and IRAS 09370-4826 are in the region IV of VH diagram (Fig. 2 (click here)). Several of these sources appear to be have thick oxygen rich circumstellar envelopes. The far infrared colours and flux distribution suggest that above mentioned sources are most likely post-AGB stars or proto-planetary nebulae similar to HD 161796 (Parthasarathy & Pottasch 1986). IRAS 08005-2356 and IRAS 09370-4826 were classified as proto-planetary nebulae by Slijkhuis (1992) and Hu et al. (1993) respectively. The LRS spectrum, IRAS colours and BVRI photometry of IRAS 09370-4826 suggest that it is a post-AGB F supergiant.
Sources in region V of VH diagram (Fig. 2 (click here)) is occupied by planetary nebulae and non-variable OH/IR stars with very cool circumstellar envelopes. some of the post-AGB stars and proto-planetary nebulae are also found in this region (van der Veen & Habing 1988). IRAS 04296+3429, IRAS 05113+1347, IRAS 07430+1115 and IRAS 09032-3953 are in region V. Some of these sources show 3.3 m and 21 m emission features indicationg that they are carbon rich. # 7 IRAS 04296+3429 It is a carbon-rich star (Loup et al. 1993). It has been detected in the CO(J=2-1) line by Woodsworth et al. (1990) and by Omont et al. (see Loup et al. 1993), obtaining and of and and and , respectively. This source has been classified as a PPN. Hrivnak et al. (1994), carried out H and K band low-resolution spectroscopic observations of this source. They also find dust features at 3.3, 3.4 and and assign a spectral type G0Ia to this source. The feature is suggested to be related to the polycyclic aromatic hydrocarbon (PAH) molecules commonly found in planetary nebulae (Buss et al. 1990).
Manchado et al. (1989), have detected this source in the JHKL bands. We find its V-K value to be 6.0 indicating that may be a highly obscured star. The observed flux distribution shown in Fig. 3 (click here). # 11 IRAS 05113+1347 Hrivnak et al. (1994) carried out H, K and L band low-resolution infrared spectroscopic observations of this source. They detected HI and CO features in absorption and also the feature (although weak). The available observations indicate that it is G type post-AGB supergiant. # 17 IRAS 07430+1115 Hrivnak et al. (1994), carried out low-resolution infrared spectroscopy of this source. Our photometry and IRAS colours and flux distribution suggest that it is a post-AGB F or G supergiant. # 21 IRAS 09032-3953 This source has been classified as a PPN by Hu et al. (1993). The CO line indicates a of and an expansion velocity of (Loup et al. 1990). A search for the optical counterpart of this source on the ESO and SERC prints by us indicates an extremely faint optical object within the IRAS error ellipse, along with a brighter object towards the north-west boundry of the error ellipse. The finding chart of this source is given in Fig. 4 (click here). Hu et al. (1993), carried out VRIJHKL photometric measurements of this object. On the basis of IRAS colours, LRS spectrum and photometry we conclude that it is a late type post-AGB supergiant. The observed flux distribution is shown in Fig. 3 (click here).
Figure 4: CCD image of the region around IRAS 09032-3953 in the V, R and I photometric bands from observations of 2 Feb. 1993. North is up and East is to the left. The scale of the figure is indicated by the length of the line drawn in the R band image which corresponds to 20 arcsec
Sources in the region VIa are characterized by non-variable stars, carbon-rich circumstellar envelopes with very cold dust at large distances. IRAS 04179+4145 and IRAS 08235-4747 are in region VIa (Fig. 2 (click here)). The LRS spectrum of IRAS 04179+4145 also indicates that it is a carbon rich object.
Sources in region VIb of VH diagram are occupied by variable stars, oxygen rich circumstellar envelopes with very cold dust at very large distances. IRAS 00409+5933 and IRAS 04278+2253 are in region VIb (Fig. 2 (click here)). Their location in B-V vs. V-I diagram suggest that they have very red colours. The IRAS flux distribution of these two sources is rather flat indicating temperature gradiant or multiple shells with a different dust temperatures.
Sources in region VII of VH diagram are characterized by carbon-rich circumstellar envelopes. IRAS 05067+2942 and IRAS 17173-4632 occupy the region VII (Fig. 2 (click here)). # 9 IRAS 05067+2942 The location of this source in the VH diagram shows that it is likely to be in the AGB phase. We present in Fig. 5 (click here) the CCD images of this source in the V, R and I bands. The double images at the position of the IRAS source which are barely resolved on the POSS Sky Survey print E, appear well resolved on the R and I band CCD images. It is seen that the object indicated by the arrow (which is most likely to be the counterpart of the far-infrared source) on the R and I band CCD images does not show up in the V band image. The image of the brighter object close to the IRAS source also appears to get fainter as we go to shorter wavelength bands, but does not show such drastic changes in brightness as the one identified to be the counterpart of the IRAS source. Because of the close proximity of the brighter source to the weaker IRAS counterpart we used ``daophot'' in crowded fields to determine the magnitudes of this source in the different wavelength bands. Our BVRI photometry of this source at two different epochs indicate that the source is a variable at the optical wavelengths also.
Figure 5: CCD image of the region around IRAS 05067+2942 in the V, R and I photometric bands from observations on 11 Jan. 1992. North is up and East to the left. The scale of the figure is indicated by the length of the line drawn in the R band image which corresponds to 20 arcsec
Sources in the region VIII of VH diagram are occupied by different sorts of obejects IRAS 05235+1129 is in the region VIII (Fig. 2 (click here)). Our BVRI photometric observations of these sources are in agreement with those obtained by Torres et al. (1995). The IRAS fluxes of this source show increasing flux from to similar to that of T Tauri stars, young stellar objects, compact H II regions and reflection nebulae.
# 27 IRAS 15269-4400 This source exhibits a silicate feature similar to the one in the spectrum of Pictoris (Fajardo & Knacke 1995) which is a wide feature with two peaks at 9 and . The spectral characteristics indicate that this type of emission originates from oxygen rich circumstellar dust. They obtain a temperature of 300 K for the dust emission from this source after subtracting the contribution from the photospheric continuum. Our BVRI photometry shows that it is a red object (Fig. 1 (click here)).