3 Discussion

3.1 Candidates to cataclysmic variables

A total of 8 cataclysmic variables were identified in our study. The finding charts for these objects, obtained from the Digitized Sky Survey (SkyView), are shown in Fig. 6.

3.1.1 CZ Aquilæ

CZ Aql was observed frequently in the 1986 mission and, on all occasions, it showed a weak blue continuum with emission lines of the hydrogen Balmer series, HeI $\lambda$5876, HeI $\lambda$6678 and a very weak HeII $\lambda$4686 (Fig. 1a).

Additional photometric and spectroscopic data collected at LNA indicate a probable value of 4.8 hours for its orbital period. The available data, including the historical photometric data of Reinmuth (1925), do not allow a description of the eruptive behaviour of this object, however the spectral signatures presented are common in dwarf novæ in quiescence (see, e.g., Warner 1995 and references therein).

  

Figure 1: Spectra of CZ Aql a), OQ Car b,c), V342 Cen d,e,f), ST Cha g,h) and KQ Mon i,j). The fluxes are in units of 10-14 erg cm-2 s-1 Å-1

3.1.2 OQ Carinæ

Spectroscopic observations of OQ Car obtained on Feb. 12, 1992 show a blue continuum with H$\alpha$ in emission (Figs. 1b and 1c), while the photometric observations reveal UV excess (Paper I) and the presence of flickering, which confirm OQ Car as a cataclysmic variable. These data are far from enough to characterize the system, however a dwarf nova classification is suggested by the amplitude of variation seen in our UBVRI data ($\sim$1 mag, in measurements separated by 3 days) and in the GCVS4 (2.5 mag). The spectral characteristics presented are also compatible with such classification. No historical photometric data have been published for this object.

3.1.3 V342 Centauri

The star V342 Cen was observed on three occasions in the CTIO mission. On the first two, it showed a blue continuum with lines of the Balmer series in absorption while in the last (9 days later) the continuum weakened and the Balmer series appeared in emission (Figs. 1d and 1e). The brightness of V342 Cen in the later occasion was about 2 mag fainter, suggesting that the first two spectra were, probably, collected while the star was in eruption. HeI $\lambda$5876 and H$\alpha$ are seen in emission in a spectrum collected at LNA on Feb. 11, 1992 (Fig. 1f).

Historical photometric data (Kruytbosch 1936) show that the brightness of V342 Cen varies in the range 14.6-16.6 mag with indication of abrupt transitions, as in eruptions. A variation of brightness of 1.7 mag in two consecutive days is seen in our UBVRI measurements, also suggesting an eruption. The same data show the occurrence of two eruptions in 15 days. The presence of a such behaviour indicate V342 Cen as a candidate to dwarf nova class, possibly of U Gem type.

3.1.4 ST Chamaeleontis

Spectroscopy of ST Cha obtained on two consecutive nights in the 1986 mission shows a blue continuum with broad and shallow Balmer absorption lines (Fig. 1g). Additional spectroscopy obtained at LNA on February 10-11, 1992 and on May 07-12, 1992 also shows a blue continuum, however H$\alpha$ and HeI $\lambda$6678 (very weak) appear in emission (Fig. 1h).

An analysis of the published photometric data of Mauder & Sosna (1975) shows that ST Cha could be an eclipsing variable, with possible values of 6.8 or 9.6 hours for the orbital period. Time series CCD photometry with $\sim$7.5 hours of duration in two consecutive nights (March 11/12, 1997) failed to detect any evidence of eclipses with such periods. Our UBVRI photometry shows on the other hand an amplitude of variation of about 2.7 mag (Paper I) while the amplitude quoted in the GCVS4 is $\Delta m=4.8$ mag. Variations of brightness with such amplitudes seem to indicate an eruptive behaviour and suggest a dwarf nova classification for this object.

3.1.5 KQ Monocerotis

In the course of our study we learned that KQ Mon is a known cataclysmic variable discovered by H.E. Bond in 1978, and classified as being of UX UMa type. Our UBV data as well as the historical data of Hoffmeister et al. (1954) do not show large fluctuations in brightness that characterize eruptions. This is consistent with the interpretation that KQ Mon is a cataclysmic variable of the UX UMa type, since these objects usually vary less than 0.5 mag on a time scales of years.

Our spectra (Figs. 1i and 1j) show a strong blue continuum with H$\alpha$, H$\beta$ and HeI $\lambda$6678 in emission, contrary to the absorption Balmer lines seen previously (Sion & Guinan 1983, and references therein). H$\alpha$ and HeI $\lambda$6678 are also seen in emission in a spectrum obtained by Zwitter & Munari (1994). KQ Mon is also classified as UX UMa by Downes & Shara (1993) and Zwitter & Munari (1994).

3.1.6 V729 Sagittarii

A spectrum obtained for this object on July 05, 1986 shows a flat continuum with Balmer lines in emission (Fig. 2a). Historical data (Ferwerda 1934) show brightness variations of $\sim$1.5 mag with recurrence time of 20-30 days. The rising part of the variations is fast ($\sim$1-2 days), even though longer (5-6 days) episodes also take place. The decline from the maximum is always longer, typically 5-8 days. Brightness variations with such time scales and characteristics suggest a dwarf nova classification for V729 Sgr. Additional observations using CCD photometry show that V729 Sgr is an eclipsing cataclysmic variable with an orbital period of 0.173 d.

  

Figure 2: Spectra of V729 Sgr a), V730 Sgr b), AN Gru c), AY Oct d), V2323 Sgr e,f), SY Vol g), V617 Sgr h), V1082 Sgr in low state i) and in high state j). The fluxes are in units of 10-14 erg cm-2 s-1 Å-1

3.1.7 V730 Sagittarii

V730 Sgr was observed spectroscopically on July 05, 1986. The spectrum showed a prominent blue continuum with H$\alpha$ weakly in emission while the other members of the Balmer series are in absorption (Fig. 2b). The presence of eruptions with amplitudes of $\sim$2-3 mag and recurrence time of 20-40 days is indicated by historical data of Ferwerda (1934). The eruptions last a few days and present a steeper rise ($\sim$1-2 days) than decline. Eruptions with such characteristics are typical of dwarf nova of U Gem type and suggest V730 Sgr as probable variable of the same type. A U Gem type for this object was also suggested by Ferwerda (1934).

3.2 Suspected cataclysmic variables

The stars AN Gru, AY Oct, V2323 Sgr and SY Vol are quoted in the literature as suspected cataclysmic variables (Vogt & Bateson 1982; Downes & Shara 1993; Kholopov et al. 1987; Downes et al. 1997).

The spectroscopic and photometric observations we made for AN Gru and AY Oct did not show the presence of characteristics usually found in cataclysmic variables, like emission lines and UV excess (Figs. 2c and 2d, Paper I). The data show brightness variations in AN Gru consistent with time scales of pulsation of RR Lyræ variables while CCD photometry of AY Oct on three consecutive times, with two days of separation, did not show brightness variation. A possible problem in the correct identification of AY Oct is pointed out by Downes & Shara (1993). Our observations refer to the object indicated in the Hoffmeister's chart (Hoffmeister 1963). Downes et al. (1997) in the 2nd ed. of their cataclysmic variables catalogue mention the presence of a RR Lyræ star 6$^{\rm s}$ east and 6$\hbox{$^{\prime\prime}$}$ north of the previous position of AY Oct. It is possible therefore that this RR Lyræ is the only variable in the field.

The star V2323 Sgr was observed spectroscopically on several occasions (see Table 1). Very prominent Balmer emission lines are seen in some spectra superposed on a continuum with very weak TiO absorption bands. In others, the continuum is fainter and of later spectral type, with the TiO bands clearly visible while the emission lines are weak or absent (Figs. 2e and 2f). These data do not confirm V2323 Sgr as cataclysmic since such variables do not display reddened optical continuum or TiO bands which such intensities. Additionally, the emission lines in cataclysmics are broader than the lines seen in this object. On the other hand, a classification as symbiotic star is also improbable since our observations do not reveal emission lines like [OIII] and HeII, whose presence associated with a late spectrum, is characteristic of this class of variables. The true classification of V2323 Sgr is not possible with our data, although the presence of a late spectrum with emission lines is seen in semiregular variables and Miras.

The variable SY Vol was observed spectroscopically on Feb. 12, 1992. The spectrum shows a blue continuum with H$\alpha$ in emission (Fig. 2g). Our CCD photometry shows flickering as well as the presence of a brightness variation of 1.8 mag in data separated by 14 days. Such characteristics confirm SY Vol as a cataclysmic variable, probably a dwarf nova. We would like to call attention to a possible problem in the correct identification of this variable in the catalogue of Downes & Shara (1993). The star we observed is the one indicated in the Hoffmeister's chart (Hoffmeister 1963), which is 2.7$^{\rm s}$ west and 19$\hbox{$^{\prime\prime}$}$ south from the object marked in the Downes & Shara's chart (see Fig. 6).

3.3 Peculiar objects

3.3.1 V617 Sagittarii

V617 Sgr is one of the most interesting objects identified in our program. It presents a very high excitation emission spectrum displaying besides the lines of the Balmer series, lines of NIII-CIII $\lambda$4640-4650, HeII $\lambda$4686 ($\sim$2.5 times stronger than H$\beta$), NV $\lambda$4945, OVI $\lambda$5290, HeII $\lambda$5412, OVI $\lambda$5584, CIV $\lambda$5802 and NIV $\lambda$6383 (Fig. 2h). Such lines are quite common in Wolf-Rayet stars. In fact, this object has number 109 in Wolf-Rayet catalogues (van der Hucht et al. 1981; van der Hucht et al. 1988).

Lundström & Stenholm (1984, 1989) have also observed this star. The incompatibility between the distance derived assuming standard intrinsic parameters of W-R stars and the small reddening seen in the direction of WR 109, led those authors to suggest a lower luminosity and indicate a classification of cataclysmic variable or low-mass X-ray binary for V617 Sgr. Our data show the presence of short time scale variability (flickering) and a short orbital period (Steiner et al. 1988). Few objects with spectra like V617 Sgr are known. Among them, V Sge (Herbig et al. 1965; Williams 1983; Echevarría et al. 1989), WX Cen (Diaz & Steiner 1995) and GQ Mus (Krautter & Williams 1989; Diaz & Steiner 1994). Figure 6 shows the finding chart for V617 Sgr.

3.3.2 V1082 Sagittarii

V1082 Sgr, like V617 Sgr, is an odd case. This object presents two brightness states in which its photometric and spectroscopic properties change completely. In the high state ($V \sim 14.0 - 14.5$), V1082 Sgr presents flickering, UV excess, and a spectrum with prominent emission lines of Balmer series, HeI and HeII while in the low state ($V\sim 15.0 - 15.5$), flickering is practically absent, the colours are red and the spectrum does not show emission lines. Figures 2i and 2j show the spectrum of V1082 Sgr in these two states. They were collected on June 28, 1986 and July 03, 1986, respectively. The continuum of the cool star is visible even in the high state and can be classified as K2-K4III.

Published photometric data (Uitterdijk 1949) show that the brightness of V1082 Sgr varies in the range 13.6-15.7 mag. These data also show the occurrence of light changes of $\sim$1 mag with time scales of $\sim$1-2 days. We propose V1082 Sgr to be a symbiotic star. A finding chart for this object is shown in Fig. 6.

3.4 Symbiotic star candidates

In our study on irregular variables we found 7 other stars which show a late-type continuum with prominent emission lines of the Balmer series, HeI and [OIII] (Table 1). The stars RT Cru, DQ Ser, DT Ser, NSV 10435 and NSV 11776 are classified as true symbiotics while V417 Cen and V704 Cen are quoted as possible candidates to this class, since these two objects did not show lines of higher excitation as HeII or [FeVII]. A more detailed discussion on these objects can be found in Cieslinski et al. (1994, 1997b).

 

Table 1: Spectroscopic data

 

Table 1: continued

 

Table 1: continued

  

Table 1: continued

3.5 NSV 07105: A Be-type object

The presence of peculiar colours in NSV 07105 (Paper I) motivated us to do spectroscopy of this object on several occasions (Table 1). The spectra show a strong blue continuum with absorption lines of the Balmer series, HeI ($\lambda\lambda$4714, 5015, 5876, 6678), SiII ($\lambda\lambda$6347, 6371), FeII $\lambda$6517 and NaI ($\lambda\lambda$5890, 5896). H$\alpha$ displays a broad component with FWHM $\sim$ 1000 km s$^{\rm -1}$ and a narrow component with FWHM $\sim$ 200 km s$^{\rm -1}$, while the other lines present only the narrow component (Figs. 3a, 3b and 3c).

  

Figure 3: Spectra of NSV 07105 a,b,c,d), V1003 Oph e), DG CrA f), V499 Ori g), XX Sct h), BN CrA i) and V576 Aql j). The fluxes are in units of 10-14 erg cm-2 s-1 Å-1. The inserted box in Fig. 3d shows a Coudè spectrum of NSV 07105 in the H$\alpha$ and HeI $\lambda$6678 region (this spectrum is not calibrated in flux)

Broad H$\alpha$ in absorption with a double peak in emission is seen in a higher resolution spectrum taken with the Coudè Spectrograph of the LNA on August 24, 1989. The separation of the emission component features is $\sim$300 km s$^{\rm -1}$ (see inserted box in Fig. 3d). H$\alpha$ with double peak in emission is seen again in a spectrum taken on March 11, 1996 (Fig. 3d).

3.6 Candidates to T Tauri stars and related objects

Three stars in our sample showed spectroscopic characteristics which permit to classify them as possible young objects. They are DW CMa, V1003 Oph and DM Ori.

The star V1003 Oph shows a weak red continuum with emission lines of the Balmer series, HeI ($\lambda\lambda$5876, 6678) and H ($\lambda$3968) and K ($\lambda$3934) of CaII (Fig. 3e). The LiI $\lambda$6707 line in absorption is seen in observations carried out by Quast & Torres (private communication) with the Coudè Spectrograph of the LNA on April 24, 1988. The presence of lines of the Balmer series and CaII in emission and LiI in absorption is characteristic of T Tauri variables (Herbig 1962). Consequently, we classify V1003 Oph as new T Tauri star. This object is listed as IN: in the GCVS4 catalogue, i.e., a probable irregular variable associated with nebulosity.

The other two stars were observed spectroscopically by Gregorio-Hetem et al. (1992) and Torres et al. (1995) in a program aiming to discover new T Tauri stars. Those authors classified DW CMa as Herbig Ae/Be object and DM Ori as T Tauri.

3.7 Objects with G-spectral type and Balmer lines in emission

Four of the observed objects present G-type continua and emission of lines of Balmer series (Table 1). In XX Sct and BN CrA only H$\alpha$ is visible while in DG CrA and V499 Ori the other members of the series can be seen (Figs. 3f, 3g, 3h and 3i).

A definitive classification for such objects is not possible with our data. The classification quoted in the GCVS4 for these variables is INS (i.e., a rapid irregular variable associated with nebulosity) for DG CrA, INS: for V499 Ori, IS (i.e., a rapid irregular with no apparent connection with nebulosities) for BN CrA and IS: for XX Sct.

3.8 Objects with K-M spectral type and Balmer lines in emission

We have found 17 objects which display late-type continua (K-M) with the Balmer series in emission (Table 1). V576 Aql, KZ Ara, V514 Ara, OQ Nor, OO Pav and V432 Sco are variables which show lines from H$\alpha$ to H$\delta$ while the others present only H$\gamma$ and/or H$\delta$ lines. Among these objects, V651 CrA shows only H$\alpha$ in emission. Examples of spectra of this group of objects are shown from Fig. 3j to Fig. 4h.

The correct classification of these variables is not obvious since Mira variables as well as red semiregular variables can sometimes present phases in which emission lines are visibles in their spectra. Consequently, more photometric and/or spectroscopic information is necessary in order to better characterize such objects. Some of them showed, however, very late M spectral type and H$\delta$ and H$\gamma$with intensities normally found in Mira variables. They are V720 Ara, V814 Ara, V531 Cen, V1257 Sgr, NSV 07097 (see Fig. 4h) and NSV 13052.

  

Figure 4: Spectra of KZ Ara a), V514 Ara b), OQ Nor c), OO Pav d), V432 Sco e), V651 CrA f,g), NSV 07097 h), NSV 05443 i) and VV Pav j). The fluxes are in units of 10-14 erg cm-2 s-1 Å-1

3.9 Carbon star candidates

NSV 05443 and VV Pav are variables whose spectra showed the presence of characteristics of carbon stars like very strong Swan bands of the $C_{\rm 2}$ molecule (with band heads at 4737, 5165 and 5635 Å) and bands of CN in the near infrared (Figs. 4i, 4j and 5a). FH Sct is another object which showed the Swan bands of $C_{\rm 2}$ at 4737, 5165 and 5635 Å (Fig. 5b). This object is classified as a variable of type R Coronæ Borealis in the GCVS4 (Kholopov et al. 1987).

Two of the stars, IK Pup and NSV 03482, show extreme red colours, similar to the NSV 05443 (Paper I). They are, consequently, candidates to carbon stars also. In fact, for IK Pup a C(N) spectral type has been assigned in the GCVS4 while for NSV 03482 we do not have spectroscopic information.

  

Figure 5: Spectra of VV Pav a), FH Sct b,c), NSV 06627 d), NSV 06989 e), MU Nor f), HR Nor g), NSV 11826 h), TU Oct i) and V688 Ara j). The fluxes are in units of 10-14 erg cm-2 s-1 Å-1

3.10 Other objects

The remaining objects of our sample (a total of 123) did not show emission lines in their spectra. The range of spectral types presented by these objects varies from early A to late M (see Figs. 5d to 5j).

The correct classification for those objects is also not possible with our data since several classes of variables can display overlapping spectral types. For example in the range F-K one can find variables like $\delta$ Cephei (Population I Cepheids), W Virginis (Population II Cepheids), RR Liræ, semiregular variables of SRD type (Kholopov et al. 1985) or even the yellow semiregular variables of RV Tauri group. On the other hand, $\delta$ Scuti and RR Liræ objects may present spectral types earlier than F, while semiregular variables of types SRA, SRB and SRC show M spectral type (Kholopov et al. 1985).

As examples of objects better observed we mention BY Aps classified by us as a Mira variable (Cieslinski et al. 1997c), V529 CrA as a probable RV Tauri variable of RVb subgroup (Cieslinski et al. 1998) and NSV 06627 as a RR Lyræ variable of ab sub-type (more information on this star will be published elsewhere).

  

Figure 6: Finding charts for CZ Aql, OQ Car, V342 Cen, ST Cha, KQ Mon, V617 Sgr, V729 Sgr, V730 Sgr, V1082 Sgr and SY Vol. The images cover 6$\times$6 arcmin, with North up and East left

Acknowledgements

We are grateful to the CTIO and LNA staffs for the observing assistance during the missions. We thank S.D. Kirhakos, G. Quast and C.A.O. Torres for sharing telescope time and the referee, U. Munari, for his valuable comments and suggestions. D. Cieslinski acknowledges the support of CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico) and FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo).