Symbiotic Stars on Asiago Archive PlatesAuthor(s): Rajka Jurdana-Šepić and Ulisse MunariSource: Publications of the Astronomical Society of the Pacific, Vol. 122, No. 887 (January2010), pp. 35-40Published by: The University of Chicago Press on behalf of the Astronomical Society of the PacificStable URL: http://www.jstor.org/stable/10.1086/650319 .

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Symbiotic Stars on Asiago Archive Plates

RAJKA JURDANA-ŠEPIĆPhysics Department, University of Rijeka, Omladinska 14, HR-51000 Rijeka, Croatia

AND

ULISSE MUNARI

INAF, Astronomical Observatory of Padova, Asiago (VI), Italy

Received 2009 October 14; accepted 2009 November 27; published 2009 December 18

ABSTRACT. The Asiago photographic archive has been searched for plates containing the symbiotic starsAS 210, AS 327, AX Per, BF Cyg, CI Cyg, DT Ser, EG And, GH Gem, Hen 2-442, Hen 3-1591, HM Sge,MaC 1-17, NSV 11776, Pe 2-16, Pt 1, PU Vul, RS Oph, T CrB, UV Aur, V1016 Cyg, V1329 Cyg, V352Aql, V4018 Sgr, Wray 15-1470, and Z And. A total of 1617 good-quality plates imaging the program stars havebeen found and their brightness has been estimated using the Henden & Munari UBVRCIC local photometricsequences. The results for the objects with most abundant measurements are discussed.

1. INTRODUCTION

Symbiotic stars are highly energetic binaries, generally com-posed by a cool giant and an accreting white dwarf companion,with orbital periods laying usually between 1 and 4 yr (or a fewdecades in the systems harboring a Mira variable, ∼20% of allknown symbiotic stars; cf. Mikolajewska 2003). There are cur-rently about 300 known symbiotic stars, and various surveysare continuously discovering new ones, both in the Milky Way(e.g., Corradi et al. 2009) and in external galaxies within theLocal Group (e.g., Goncalves et al. 2008). A good fraction ofthe symbiotic stars are powered by stable H burning, at the sur-face of a white dwarf, of the material transfered from a coolgiant companion. This was theoretically predicted by Tutukov& Yungelson (1976), and Pacinski & Rudak (1980), and con-firmed observationally by Munari & Buson (1994), Greiner(1996), and Sokoloski (2003). As such, the symbiotic stars area possible channel to form SN Ia (Munari & Renzini 1992;Hachisu et al. 1999). In fact, at least a fraction of the whitedwarfs in symbiotic stars are massive as indicated by the pres-ence of recurrent novae among them (e.g., RS Oph, T CrB,V3890 Sgr, V745 Sco; Anupama & Mikolajewska 1999),and the accretion process is not accompanied by significantmass loss from the system (e.g., Meier et al. 1994). A paralleland fainter population of symbiotic stars, where the degeneratecomponent is a neutron star, is now being recognized (e.g.,Masetti et al. 2006; Nespoli 2009).

The symbiotic stars show variability over any time scale fromminutes (flickering) and years (orbital motion), to several de-cades (outbursts of symbiotic novae). These long time scalesrequire assembling data from as many different sources as pos-sible to reconstruct a usable light curve. Mining of historicalplate archives still maintained at some observatories around

the world plays a crucial role in this data collection. The large,and sometimes unexpected, wealth of information obtained withthe reconstruction of historical light curves of symbiotic starsis testified by the examples of YY Her (Munari et al. 1997), AXPer (Skopal et al. 2001), or BF Cyg (Leibowitz & Formiggini2006) among others (cf. Kenyon 1986 and Skopal 2008 fordiscussions).

In this article we present abundant new photometric data for25 symbiotic stars, obtained from historical photographic plates(exposed between 1958 and 1998) found in the archives of theAsiago Schmidt telescopes.

2. THE DATA

We have already systematically searched the Asiago archivefor historic plates imaging symbiotic stars. Munari et al. (2001)presented 602 measurements of seven objects, and Munari &Jurdana-Šepić (2002) provided an additional 635 photometricmeasurements of a second sample of eight symbiotic stars.The present article completes the search by proving 1617 mea-surements of other 25 symbiotic stars. Table 1 lists the starsconsidered in this final paper, while Table 2 (full table avail-able in the electronic version of this article) gives all themeasurements.

As for our previous two papers dealing with Asiago plates,the magnitudes of the program stars were estimated at a micro-scope against the local UBVRCIC photometric sequences cali-brated by Henden & Munari (2000, 2001, 2006). During themeasurements, 120 plates imaging the program stars wererejected because of either low quality (poor focus or seeing,fogged background) or unsuitable emulsion-filter combina-tion. Further details (including plate number, exposure time,

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emulsion and filter type, individual plate notes, etc.) are avail-able, as for previous papers in this series.1

The vast majority of the derived magnitudes are in the Bband (1151), followed by V (294), IC (163), and RC (9) bands.The reported data and errors are given in steps of 0.05 mag. InTable 2, symbols < and > are used to indicate that the programstar was, respectively, brighter or fainter than the brightest orfaintest star of the photometric comparison sequence (whosemagnitude is given in the table) imaged on the given plate.

3. RESULTS

A detailed discussion of the photometric data presented foreach program star is far beyond the scope of this article, espe-cially considering the popularity of many of them. In this sec-tion, we briefly outline the results obtained for some of thesystems with the most abundant measurements here presented.

V1329 Cyg. The light curve based on the B-band data givenin this article is presented in Figure 1. It is characterized by alarge sinusoidal modulation (of 953 day period and 1.2 mag

amplitude) superimposed onto a very slow decline (correspond-ing to a loss of one magnitude in 20 yr). Figure 1 also plots thecorresponding data from Stienon et al. (1974), Skopal et al.(1992) and Hric et al. (1994), showing a good agreementbetween the various data sets. V1329 Cyg erupted in outburstin the 1960s, peaking at a maximum B ∼ 11:5 in the summer of1965, and since then it has been very slowly declining towardquiescence. The latter has not been yet reached, the objects stillbeing (at the time of writing) ∼0:75 mag brighter than beforethe outburst, when it rested at B ∼ 15:0. In quiescenceV1329 Cyg displayed sharp eclipses with the same period asthe sinusoidal variation in Figure 1 (Munari et al. 1988b). Thesinusoidal variation has been variously ascribed to a rethermal-ization of the hot star radiation by the red giant atmospherecloser to it (historically termed a reflection effect) or as the resultof a different projection of the optically thick part of the ionizedzone onto the line of sight (e.g., Kenyon 1986; Proga et al. 1996;1998; Skopal 2001, 2008).

V352 Aql. The object was discovered by Hoffmeister et al.(1954) during an outburst that peaked at mpg ¼ 13:3 in 1928and then declined very slowly (t3 > 6 yr). Duerbeck & Seitter(1989) identified the object in quiescence as a symbiotic star

TABLE 1

PROGRAM STARS

Object N Bð Þ N Vð Þ NðRCÞ NðICÞ First Observation Last Observation

AS 210 . . . . . . . . . . . . . . . . . . 5 1 1970 05 02 1976 05 28

AS 327 . . . . . . . . . . . . . . . . . . 16 1 7 1961 06 16 1984 07 31

AX Per . . . . . . . . . . . . . . . . . . 6 1 1976 11 23 1985 12 18

BF Cyg . . . . . . . . . . . . . . . . . . 26 20 1965 10 28 1989 11 27

CI Cyg . . . . . . . . . . . . . . . . . . 217 45 8 1959 07 31 1995 08 14

DT Ser . . . . . . . . . . . . . . . . . . . 11 10 1972 07 16 1977 10 03

EG And . . . . . . . . . . . . . . . . . 257 10 1958 09 06 1993 01 17

GH Gem . . . . . . . . . . . . . . . . . 13 1967 01 11 1981 01 06

Hen 2-442 . . . . . . . . . . . . . . . 40 15 1 3 1965 10 28 1985 07 22Hen 3-1591 . . . . . . . . . . . . . . 41 2 27 1961 06 16 1976 08 02

HM Sge . . . . . . . . . . . . . . . . . 20 14 2 1 1976 07 23 1998 10 22MaC 1-17 . . . . . . . . . . . . . . . 27 6 1961 06 15 1982 09 15

NSV 11776 . . . . . . . . . . . . . . 29 7 1961 06 16 1995 06 27

Pe 2-16 . . . . . . . . . . . . . . . . . . 40 5 1961 06 16 1991 06 15

Pt 1 . . . . . . . . . . . . . . . . . . . . . . 10 1 10 1971 09 11 1974 09 10

PU Vul . . . . . . . . . . . . . . . . . . 37 16 2 1967 07 09 1985 08 13

RS Oph . . . . . . . . . . . . . . . . . . 43 16 1965 03 29 1991 06 15

T CrB . . . . . . . . . . . . . . . . . . . . 39 10 1966 02 16 1986 08 02

UV Aur . . . . . . . . . . . . . . . . . . 1 3 1983 11 10 1970 02 07

V1016 Cyg . . . . . . . . . . . . . . 41 18 1965 11 24 1985 09 11

V1329 Cyg . . . . . . . . . . . . . . 79 36 7 1969 10 13 1987 12 19

V352 Aql . . . . . . . . . . . . . . . . 74 47 1 79 1965 06 27 1995 09 26V4018 Sgr . . . . . . . . . . . . . . . 25 2 1985 09 11 1961 05 10

Wray 15-1470 . . . . . . . . . . . 23 1 8 1966 03 22 1976 05 27

Z And . . . . . . . . . . . . . . . . . . . 32 22 1965 10 23 1981 11 03

NOTE.—The number of plates in each photometric band is listed together with the date of the first and last plate.

1 At http://ulisse.pd.astro.it/symbio_pg/.

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shining atB ∼ 18:3, V ∼ 15:7. Their spectrum shows anM giantabsorption spectrum, with superimposed intense Balmer, He I,and He II emission lines. The UBVRCIC photometric catalogof symbiotic stars of Henden & Munari (2008) reports forV352 Aql on 2001 September the mean values ⟨B⟩ ¼ 18:35,⟨V ⟩ ¼ 16:61, ⟨IC⟩ ¼ 13:13. Not much more is known aboutthis faint symbiotic star. Our B, V , IC light curve of V352Aql covers the period from 1970 to 1995 and is presented inFigure 2. It is characterized by quiet behavior around the meanvalues ⟨B⟩ ¼ 17:66, ⟨V ⟩ ¼ 16:60, ⟨IC⟩ ¼ 13:26, with no otheroutburst recorded after the original one in 1928. A variability ofseveral tenths of a magnitude around these mean values are evi-dent in our data. We performed extensive Fourier analysis butfound no evident periodicity.

Hen 3-1591. It was discovered on objective prism plates byHerbig (1969) as a G/K star with weak [O III], [Ne III], andHβ emission lines. A quite different spectral appearance wasreported by Sanduleak & Stephenson (1973), and further spec-

troscopy by Allen (1978), Medina Tanco & Steiner (1995),Gutierrez-Moreno & Moreno (1996), and Munari & Zwitter(2002) have clearly established a significant spectral variabilityof Hen 3-1591. Apart from a preliminary report of a possiblevariability by Hoffleit (1970), no photometric investigation ofthis star has been carried out. The photometric catalogs of sym-biotic stars by Munari et al. (1992) and Henden & Munari(2008) report U ¼ 14:52, B ¼ 14:06, V ¼ 12:96, RC ¼ 12:26,IC ¼ 11:67 for 1990 March 27, and U ¼ 14:96, B ¼ 14:36,V ¼ 13:14, RC ¼ 12:40, IC ¼ 11:70 for 2002 April, respec-tively. Our light curve of Hen 3-1591 is presented in Figure 3.It covers the period from 1961 to 1976 and it is characterizedby the mean values B ¼ 14:08 and IC ¼ 11:61. In spite of thespectral variability, Hen 3-1591 seems photometrically quitestable. Some slow and low amplitude variability in the B bandseems nevertheless present in Figure 3, with Hen 3-1591 in1972 and 1973 rising to a mean B ¼ 13:85, i.e., 0.2 mag bright-er than the average quiescence value.

EG And. Thanks to its brightness, EG And is a quite popularobject. It has never displayed outbursts and the luminosity of thewhite dwarf companion is lower than in other symbiotic stars(Muerset et al. 1991). Spectroscopic orbits have derived orbitalperiods around 481 days: 481.1 according to Munari et al.(1988a); 480.7, Kenyon (1992); 481.2, Munari (1993); and482.57, Fekel et al. (2000). Wilson & Vaccaro (1997) arguedthat the light curve of EG And in quiescence is dominatedby the ellipsoidal distortion of the cool giant filling its Rochelobe and not by the irradiation effect (caused by the hard radia-tion of the white dwarf being rethermalized by the facing por-tion of the cool giant atmosphere). They modeled the B and Vlight curves adopting a period of 482.0 days, a Roche lobe-filling giant, and a negligible contribution by other sources inthe system. In the bottom panel of Figure 4 we have phase-plotted our observations of EG And using the same T ∘ andP of Wilson & Vaccaro (1997). The light curve looks quite poorand scattered, with no sign of the double maxima and doubleminima typical of ellipsoidal variations. We have searched

FIG. 1.—B band light curve of V1329 Cyg with superimposed sinusoid of P ¼ 953 days and a linear decline of 0:00014 mag day�1. Dots: Asiago photographicplates; crosses: Stienon et al. (1974); plus signs: Hric et al. (1994); triangles: Skopal et al. 1992.

TABLE 2

PHOTOMETRY OF THE PROGRAM STARS ON THE ASIAGO ARCHIVE PLATES

Object Date HJD Magnitude Error

V1329 Cyg . . . . . 1969 10 13 2440508.3415 B ¼ 12:50 0.10V1329 Cyg . . . . . 1969 10 13 2440508.3519 V ¼ 11:80 0.10V1329 Cyg . . . . . 1970 06 11 2440748.5335 B ¼ 12:50 0.10V1329 Cyg . . . . . 1970 06 11 2440748.5870 V ¼ 12:30 0.10V1329 Cyg . . . . . 1970 06 12 2440749.5516 B ¼ 12:65 0.10V1329 Cyg . . . . . 1970 06 25 2440763.4705 V ¼ 12:30 0.10V1329 Cyg . . . . . 1970 07 05 2440773.4684 B ¼ 12:65 0.10V1329 Cyg . . . . . 1970 07 11 2440778.5152 B ¼ 12:85 0.10V1329 Cyg . . . . . 1970 07 11 2440778.5312 V ¼ 12:30 0.10V1329 Cyg . . . . . 1970 07 26 2440794.4966 V ¼ 12:25 0.10V1329 Cyg . . . . . 1970 07 28 2440796.4411 B ¼ 13:20 0.10V1329 Cyg . . . . . 1970 08 25 2440824.4054 B ¼ 13:20 0.10V1329 Cyg . . . . . 1970 08 25 2440824.4186 V ¼ 12:80 0.10

NOTE.—Table 2 is published in its entirety in the electronic edition of thePASP. A portion is shown here for guidance regarding its form and content.

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FIG. 3.—B and IC light curves of Hen 3-1591.

FIG. 2.—B, V , and IC light curves of V352 Aql. v symbol: fainter than.

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the period range 470–490 days looking for a value of the periodthat would produce a light curve of the type expected fromellipsoidal distortion. The only successful period we found isP ¼ 479:28� 0:03 days, and the corresponding light curveis presented in the top panel of Figure 4. It is dominated bythe irradiation effect with an amplitude ΔB≈ 0:2 mag, whilethe secondary minimum that could be ascribed to a superim-posed ellipsoidal distortion has a depth of only ΔB≈ 0:1 mag.We do not attach much significance to this possible detection ofan ellipsoidal distortion for several reasons: (1) the correspond-ing 479.28 day period is too far off the ∼481 day orbital one;

(2) several closely spaced periods around the 481 day orbitalone produce good light curves, all of the irradiation/reflectiontype, with no evidence for the ellipsoidal distortion (i.e., no sec-ondary minimum around phase 0.5); and (3) the secondaryminimum of the 479.28 day light curve occurs at phase 0.6, sig-nificantly off the expected 0.5 phase. In conclusion, we believethere is as yet no convincing evidence for an ellipsoidal distor-tion of the cool giant in EG And, and that beating with the low-level erratic variability of the hot component could introducespurious features in the orbitally phased light curves that couldmimic the presence of ellipsoidal distortions. The very low

FIG. 4.—B-band light curves of EG And folded to 479.28 day and 482.0 day periods (see text for details). To reduce the scatter, the original data in Table 2 have beenbinned into averages spanning 0.05 in phase, and the error bars represent the errors of the mean.

FIG. 5.—B light curve of PU Vul. FIG. 6.—B light curve of CI Cyg.

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luminosity of the WD in EG And also argues in favor of a masstransfer far lighter that expected from Roche lobe filling.

PU Vul. The light curve of the outburst of the symbiotic novaPU Vul has been described in detail by Kolotilov et al. (1995).The light curve built with the data of this article is presented inFigure 5. It is in excellent agrement with that of Kolotilov et al.:it displays the same rise to maximum during 1978–1979, the flatand prolonged maximum, and the deep eclipse with minimumbrightness reached around JD 2,444,500 (1980 September).What is a novel contribution of this article is the two platesimaging the object in 1967 July and November, 10 yr before theoutburst onset and consequent discovery of the object. Theynicely fill a large gap in the pre-outburst light curve of PU Vulpresented by Liller & Liller (1979) and derived from extensiveexamination of the Harvard plate archives. The B ¼ 16:1 wederived on both Asiago plates for 1967 is very close to the aver-age B ¼ 16:0 that Liller & Liller found for PU Vul over theperiod 1895–1957 covered by the Harvard plates. This supports

the notion that PU Vul spent a very long period in quiescenceprior to the outburst started in 1979 that has not yet concluded.

CI Cyg. Our B-band light curve of CI Cyg is presented inFigure 6. It covers the period from 1959 to 1989, with an iso-lated observation from 1995. The mean quiescence value isB ∼ 12:5, identical to that reported by various sources summa-rized by Kenyon (1986). Our light curve covers also the verycomplex outburst phase (composed of several maxima andsuperimposed deep eclipses) that CI Cyg experienced between1971 and 1981. The Asiago plates are however not numerousenough to cover all the ups and downs displayed by CI Cygduring this outburst phase (well depicted by, e.g., Belyakina1983). Our values from the Asiago plates well match the avail-able literature (e.g., Ruitz 1992).

Thanks are due to the anonymous referee for useful com-ments. R. J. Š. wishes to express thanks for the hospitalityof the Asiago Observatory, and to the Primorsko-GoranskaCounty for financial support.

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