Photometry of symbiotic stars XI. EG And, Z And, BF Cyg, CH Cyg, CI Cyg, V1329 Cyg, TX CVn,
a r
X
i
v
:a
s t
r o
-
p
h
/
4
2
1
41
v
1
6
F
e b
2
4
Contrib.Astron.Obs.Skalnat′e Pleso 34,1–25,(2004)
?Visiting Astronomer,San Pedro Observatory
2 A.Skopal,T.Pribulla,M.Vaˇn ko,Z.Veliˇc,E.Semkov,M.Wolf,and A.Jones
new visual estimates showed a transient disappearance of a wave-like mod-ulation in the star’s brightness between the minima at epochs E=66and E=68and its reappearance.AG Peg:Our measurements from the end of 2001showed rather complex pro?le of the LC.R W Hya:Observations follow behaviour of the wave-like variability of quiet symbiotics.AX Per:In May 2003a0.5mag?are was detected following a rapid decrease of the light to a minimum.QW Sge:CCD observations in B,V,R C,I C bands cover a period from1994.5to2003.5.An increase in the star’s brightness by about1mag was observed in all passbands in1997.Less pronounced brightening was detected in1999/2000.V934Her:Our observations did not show any larger variation in the optical as a reaction to its X-ray activity.
Key words:Techniques:photometry–Stars:binaries:symbiotic
1.Introduction
The symbiotic stars are currently understood as interacting binary systems con-sisting of a cool giant and a hot compact star,which is in most cases a white dwarf.Typical orbital periods are between1and3years,but they can be sig-ni?cantly larger.The mass loss from the giant represents the primary condition for appearance of the symbiotic phenomenon.A part of the material lost by the giant is transferred to the more compact companion via accretion from the stel-lar wind or Roche-lobe over?ow.This process generates a very hot(T h≈105K) and luminous(L h≈102?104L⊙)source of radiation.On the basis of the way in which the generated energy is being liberated,we distinguish two phases of symbiotic binary.Quiescent phases during which the hot component releases its energy approximately at a constant rate and spectral distribution.Generally, we observe a wave-like variation in their LCs as a function of the orbital phase. During active phases the hot component radiation changes signi?cantly,which leads to a2-3mag brightening of the object in the optical.A common feature of active phases is a high-velocity mass ejection.
Generally,the hot radiation ionizes a fraction of the neutral circumbinary material,which gives rise to a strong nebular emission.This component of ra-diation is physically displaced from the hot star and its optically thick part can be very complex in its shape.In addition,its location and shaping in the binary depend on the level of the activity.As a result we often observe un-expected variation in the LCs as,for example,?ares,drops in brightness,the e?ect of eclipses and outbursts.A very interesting feature of variability in this respect is the e?ect of eclipses,which is very sensitive to physical displacement and radiative contributions of individual components in the system.In the case that a signi?cant fraction of radiation at the wavelength under consideration comes from the region which is subject to eclipse,a minimum in the LC is well observable.In the opposite case,the eclipse e?ect is very faint.Therefore the eclipse e?ect can be observed only at speci?c brightness phases,at which the
Photometry of symbiotic stars XI.3 radiative contribution from a pseudophotosphere in the optical rivals that from the nebula.
Accordingly,to reveal the above mentioned peculiarities in the LCs of sym-biotic stars,it requires a very careful long-term monitoring programme.In this paper we present the recent observational results of such our programme ob-tained during the period December2001to December2003.We note that this paper continues the work of Skopal et al.(2002,hereafter S+02,and references therein).
2.Observations
The majority of the U,B,V,R measurements were performed in the standard Johnson system using single-channel photoelectric photometers mounted in the Cassegrain foci of0.6-m re?ectors at the Skalnat′e Pleso(hereafter SP in Ta-bles)and Star′a Lesn′a observatories(SL).Values in tables represent means of the whole observing https://www.wendangku.net/doc/fa3119661.html,ually,a1-hour cycle contained about10to20 individual di?erences between the target and the comparison.This approach reduced the inner uncertainty of such the means to～0.020,～0.005,～0.005 and～0.005mag in the U,B,V and R?lter,https://www.wendangku.net/doc/fa3119661.html,rger uncertainties (about0.1mag)during some nights are marked in tables by’:’.Further details about observation procedure are given in Skopal et al.(1990).
Some observations in the B and V bands were made with the50/70/172cm Schmidt telescope of the National Astronomical Observatory Rozhen,Bulgaria (R).Other details about utilities and treatment of observations as well as stan-dard stars were already presented in S+02.
The U,B,V observations of RW Hya and IV Vir were carried out at the San Pedro M′a rtir Observatory,Baja California,Mexico(M),in2003April.Also in this case further details are given in S+02.
Observations of QW Sge were performed by one of us(ZV)at his private station Beluˇs a near Povaˇz sk′a Bystrica(PB)with a Newton180/700telescope equipped with a CCD camera based on the Texas Instruments chip TC211 (from01/01/2002the chip was changed to TC-237B).A set of B,V,R,I ?lters for a modi?ed Johnson-Kron-Cousins system was used.All frames were dark subtracted and?at?elded.Transformation to the international system was made by measuring the standard stars in the star-cluster M67.Magnitudes of comparison stars were obtained in the same way as described in Hric et al. (1996).In?uence of a few arcsec distant companion(F0V star reddened with E B?V=0.20,U=13.84,B=13.59,V=13.14,R=12.53and I=11.52, Munari,Buson(1991))has not been subtracted.
In addition,2800visual magnitude estimates of AR Pav were obtained dur-ing1982.2–2003.9by one of us(AJ)with a private12”.5f/5re?ector.Other details concerning observations of AR Pav can be found in Skopal et al.2001).
4 A.Skopal,T.Pribulla,M.Vaˇn ko,Z.Veliˇc ,E.Semkov,M.Wolf,and A.Jones
3.Results
3.1.EG And
We measured EG And (HD 4174,BD+39167)with respect to HD 4143(SAO 63-173,BD+372318).To obtain magnitudes in B and V we used the standard star HD 3914(V =7.00,B ?V =0.44)and conversion between both stars,HD4143–HD3914=4.640,2.722and 1.563in the U ,B and V bands,respectively (Hric et al.1991).
The data are compiled in Table 1.Figure 1shows recent observations in U and B .At/around JD 2452600(November 2002)the primary minimum oc-curred in the U -LC.It is relatively narrow in pro?le with respect to those previously observed (e.g.at ～JD 2451160,see Fig.1).A broad wave-like vari-ation is less pronounced and,in addition,a 0.2–0.3mag brightening in U was detected by the latest observations in the autumn of 2003.These changes mean that the nebular component of radiation decreased and,instead,a pseudopho-tosphere with a more signi?cant contribution in the optical was created around the central star.In such a case the light in U should be rather of stellar nature.This view should be con?rmed by spectroscopic observations.
-2-1.5
-1
50000505005100051500520005250053000
1996
19971998199920002001200220032004M a g n i t u d e Julian date - 2 400 000
Figure 1.The U and B LCs of EG And.Arrows mark positions of the primary min-ima.New data are plotted to the right of the vertical dotted line.
3.2.Z And
This star (HD 221650)was measured with respect to the comparison SAO 53150(BD+474192;V =8.99,B ?V =0.41,U ?B =0.14,V ?R =0.16).Other details are the same as in S+02.Results are given in Table 2.
Figure 2shows our photometric observations from 2000covering a recent major outburst with the beginning at September 2000and a maximum in De-
Photometry of symbiotic stars XI.5 Table1.U and B observations of EG And
Date JD24...Phase??U B V?R Obs
6 A.Skopal,T.Pribulla,M.Vaˇn ko,Z.Veliˇc,E.Semkov,M.Wolf,and A.Jones
Table2.U,B,V,R observations of Z And
Date JD24...Phase?U B V R Obs
Photometry of symbiotic stars XI.7
910
11
12
51500520005250053000
2000200120022003
2004M a g n i t u d e Julian date - 2 400 000
Figure 2.The U,B,V photometry of Z And covering the recent active phase.The eclipse of the active component by the red giant is denoted by E .
of this star.However,the pro?le of the LC is not a simple sinusoid through the orbital cycle.It di?ers in many details from cycle to cycle.Generally,such behaviour re?ects a complex shape and variation of the nebula in the binary (Skopal 2001).For example,the minimum around JD 2452160was rather ?at for about 110days (best seen in B ).The current minimum (～JD 2452930)seems to follow the same behaviour,but very close to its mid (?=0.986,see Table 3)we detected a dip in U (=13.08)and B (=13.52),which represents the lowest brightness ever observed for BF Cyg.We note that shortly after this detection,on 15th October 2003(?=0.996),BF Cyg fell down in its brightness under the limit of detection within our devices (data quality was poor due to high background).The latest observations follow those taken just prior to this dip (Fig.3).Additional peculiarity in the LC developed in February 2003in a form of a short-term ?are.This transient brightening lasted for about 1month (our observations did not record its accurate pro?le)and was most pronounced in B (?B ～0.7mag).It occurred at the orbital phase 0.68,very close in the phase to that observed for AX Per (see below,Sect.3.12).The nature of such brightening is not well understood.It di?ers from ?ares/outbursts currently observed for other symbiotics (e.g.AG Dra,here in Fig.7),amplitude of which is largest in U .
3.4.CH Cyg
Our new photometry of CH Cyg is listed in Table 4.Stars HD 183123(SAO 48428,V =8.355,B ?V =0.478,U ?B =–0.031,V ?R =0.312)and HD 182691(SAO 31623,V =6.525,B ?V =–0.078,U ?B =–0.24,V ?R =0)were used as a comparison and a check star,respectively.In addition,we also measured
8 A.Skopal,T.Pribulla,M.Vaˇn ko,Z.Veliˇc ,E.Semkov,M.Wolf,and A.Jones
1112
13
51500520005250053000
2000200120022003
2004M a g n i t u d e Julian date - 2 400 000
Figure 3.The UBV LCs of BF Cyg.A small ?are developed in February 2003.the nearby star SAO 31628(BD+49?2997)to examine its variability suggested by Sokoloski,Stone (2000).However,our type of measurements was not suitable for such a short-period variable (P orb =3.74783d).We were able to con?rm only the position of the primary minimum according to the ephemeris suggested by Sokoloski,Stone (2000).Further observations are required to determine the whole LC-pro?le.
Figure 4shows the recent photometric observations covering the last 1998-00activity including the eclipse at the outer,14.5-year period,orbit.Our new observations indicated evolution in LCs,which is similar to that occurred after the previous active phases,in 1970,1987and 1996.5(see Fig.1of Eyres et al.2002).This is characterized by a 750-day wave-like variation in LCs and rather bright magnitudes (V ～7?7.5,B ～9?9.5and U ≈10).The colour indices are typical for a quiescent phase of this star.At ～JD 2452730a shallow minimum occurred in the UBV LCs.Its position is very close to that predicted according to the ephemeris,Min =JD 2445888+756×E (Skopal 1995).
3.5.CI Cyg
The photometric measurements of CI Cyg are given in Table 5.Stars HD 226107(SAO 68948;V =8.55,B ?V =–0.04,U ?B =–0.33)and HD 226041(SAO 68923;V =8.60,B ?V =0.35,spectrum F 5)were used as the comparison and check,respectively.
We started monitoring of CI Cyg from September 30,2002(the orbital phase ?=0.53,see Table 5,Fig.5).At that time it was around its maximum,which lasted to about March 2003(?～0.75)with a small diminution in U .Then the star’s brightness was decreasing to a minimum at ?～0by about of 1mag in U and B and by about 0.5mag in V .Such behaviour is typical for a quiescent
Photometry of symbiotic stars XI.9
Table3.U,B,V,R observations of BF Cyg.A few points were added from the VSNET database.
Date JD24...Phase?U B V?R Obs
10
A.Skopal,T.Pribulla,M.Vaˇn ko,Z.Veliˇc ,E.Semkov,M.Wolf,and A.Jones 7
8910
11
12
51000515005200052500530001998
199920002001200220032004M a g n i t u d e Julian date - 2 400 000
Figure 4.The UBV LCs of CH Cyg.
by Belyakina,Proko?eva (1991),who ascribed it to the cool giant in CI Cyg.
11
12
1351500520005250053000
20002001200220032004
M a g n i t u d e Julian date - 2 400 000
Figure 5.The UBV LCs of CI Cyg.
3.6.V1329Cyg
Our observations of the symbiotic nova V1329Cyg (HBV 475)are given in Ta-ble 6.In this paper we present only the CCD observations made at the Rozhen Observatory.The stars BD+354290(V =10.34,B ?V =1.07,U ?B =0.88)and BD+354294(V =10.16,B ?V =1.07)were used as the comparison and check,respectively.
Photometry of symbiotic stars XI.11 Table4.U,B,V,R observations of CH Cyg
Date JD24...Phase?U B V?R Obs
12 A.Skopal,T.Pribulla,M.Vaˇn ko,Z.Veliˇc,E.Semkov,M.Wolf,and A.Jones
Table5.U,B,V observations of CI Cyg
Date JD24...Phase?U B V?R Obs
Oct04,0252552.3620.95514.8613.94R
Oct05,0252553.2700.95614.8613.96R
Oct29,0252577.2670.98114.7813.92R
Oct30,0252578.2500.98314.7613.91R
Nov28,0252607.1960.01314.6213.80R
Apr03,0352732.6090.14414.1513.28R
May03,0352762.5290.17514.0813.20R
May05,0352765.4990.17814.0913.22R
Aug06,0352858.4330.275–13.17VSNET
Aug15,0352867.4580.284–12.98VSNET
Aug28,0352880.4080.298–12.79VSNET
Sep27,0352910.2460.32913.6612.95R
Sep28,0352911.3450.33013.6612.93R
Oct02,0352915.3710.33413.6913.00R
?JD
=2427687+958.0×E(Schild,Schmid1997)
eclipse
Photometry of symbiotic stars XI.13U ?B =–0.07),were used as a comparison and a check star,respectively.
Figure 6shows our recent U,B,V measurements.With respect to the evo-lution in the historical LC,TX CVn still remains at a high level of its activity (B ～10.5),while at low stages the photographic LC was at m pg ～11.6(see Fig.1of Skopal et al.2000b).In addition,we indicated two brightenings on our recent U,B,V LCs.First occurred at the end of 1996and the second one at the beginning of 2003.During both we detected a minimum,which can be ascribed to the eclipse of the active component by its cool giant companion in the TX CVn binary.The reasons are as follows:(i)The minima occurred very close to the inferior conjunction of the giant according to solution for the spectroscopic orbit as proposed by Kenyon,Garcia (1989)and,(ii)both min-ima were more pronounced in U than in B .The mid points of these minima (JD 2450477.6±1.0and JD 2452660±10)suggest the orbital period
P orb =198.4±0.9days,
which agrees within uncertainties with that suggested by Kenyon,Garcia (1989)for a circular orbit solution.The eclipsing nature of the observed minima suggest a high inclination of the orbital plane of TX CVn.
10
11
505005100051500520005250053000
19971998199920002001
200220032004M a g n i t u d e Julian date - 2 400 000
Figure 6.The UBV LCs of TX CVn.Eclipses of the active star by its giant companion are denoted by E .
3.8.AG Dra
Our measurements of AG Dra are summarized in Table 8.Stars BD+67925(SAO 16952,V =9.88,B ?V =0.56,U ?B =–0.04)and BD+67923(SAO 16935,V =9.46,B ?V =1.50,U ?B =1.89)were used as the comparison and check,respectively.
14 A.Skopal,T.Pribulla,M.Vaˇn ko,Z.Veliˇc,E.Semkov,M.Wolf,and A.Jones
Table7.U,B,V,R observations of TX CVn
Date JD24...Phase?U B V?R Obs
Photometry of symbiotic stars XI.15
910
11
5100051500520005250053000
1999
20002001200220032004M a g n i t u d e Julian date - 2 400 000
Figure 7.The UBV LCs of AG Dra.
3.9.R W Hya
The U,B,V measurements of RW Hya (HD 117970)are listed in Table 9.The observation was carried out at the San Pedro Observatory during April 2003,at its orbital phase ?～0.75.Note that the orbital period is very close to just 1year (Table 9).Stars HD 118102(CD-2410984;V =8.944,B ?V =0.528,U ?B =0.105),HD 117971(CD-259879;V =9.688,B ?V =0.439,U ?B =–0.034)and HD 117803(CD-2410970;V =8.925,B ?V =0.417,U ?B =–0.025)were used as standard stars,to which RW Hya was compared.
Magnitudes are brighter,mainly in the U band,with respect to our previous observations made at ?～0.89.This is in a good agreement with the wave-like variation as a function of the orbital phase suggested by visual estimates (see Fig.7of S+02).Observations at other positions of the binary,mainly at ?～0.5,are very desirable.
3.10.AR Pav
Figure 8shows the visual LC from 1982to December 2003.Some qualitative discussion of a major part of these data can be found in Skopal et al.(2000b,2001).Our new visual estimates cover the period from the epoch 67(1999.8,bottom panel of Fig.8).The most interesting feature of LC is a transient disap-pearance of a wave-like modulation of the star’s brightness as a function of the orbital phase for the period of just two cycles,between the minima at epochs E =66and E =68.Also variation in the depth of the minima (e.g.minima at E =61,68are by about 0.3-0.4mag brighter than those at E =64)and in its pro?le (see also Fig.2of Skopal et al.2001)re?ect a strong variation in both geometry and radiation of the active component of AR Pav.The latest obser-
16 A.Skopal,T.Pribulla,M.Vaˇn ko,Z.Veliˇc,E.Semkov,M.Wolf,and A.Jones
Table8.U,B,V,R observations of AG Dra
Date JD24...Phase?U B V?R Obs
Photometry of symbiotic stars XI.17 Table9.U,B,V observations of RW Hya
Date JD24...Phase?U B V Obs
18
A.Skopal,T.Pribulla,M.Vaˇn ko,Z.Veliˇc ,E.Semkov,M.Wolf,and A.Jones 910
11
12
13450004600047000480004900050000510005200053000
1985
199019952000M a g n i t u d e Julian date - 2 400 000
910
11
12
13
5100051500520005250053000
1998
199920002001200220032004M a g n i t u d e Julian date - 2 400 000
Figure 8.Top:Our visual estimates from 1982.2to date (made by Albert Jones).Bottom:Recent evolution covering a low stage between epochs 66and 68.
followed by a rapid decrease of the light.Its phase position (?～0.72)and other characteristics are similar to that observed in the BF Cyg LC (Sect.3.3).
3.13.QW Sge
Figure 11shows our CCD B,V,R J ,I J photometry.We converted our measure-ments in the I C and R C bands of the Cousins system into the Johnson system according to Bessell (1983)by using his transformation equations for M giants:
(V ?R )J =2×(V ?R )C ?0.48,(R ?I )J =(R ?I )C +0.10.(1)Observations cover the period from 1994.5to 2003.5and are given in Table 12.Particularly interesting part of the LCs includes an active phase,which began
Photometry of symbiotic stars XI.19
89
1050000505005100051500520005250053000
1996
19971998
199920002001200220032004M a g n i t u d e Julian date - 2 400 000
Figure 9.UBV LCs of AG Peg.Data to 1998are from Tomov,Tomova (1998).
Table 10.U,B,V,R observations of AG Peg
Date JD 24...Phase ?U B V ?R Obs
20 A.Skopal,T.Pribulla,M.Vaˇn ko,Z.Veliˇc ,E.Semkov,M.Wolf,and A.Jones
1112
13
51500520005250053000
2000200120022003
2004M a g n i t u d e Julian date - 2 400 000
Figure 10.The UBV LCs of AX Per.A small ?are developed here in May/June 2003.at 1997May and showed two maxima in 1997November and at the beginning of 2000in all wavelengths.The latter is poorly covered,because of a season gap.Amplitudes of the ?rst brightening were ?B =1.3mag,?V =1.4mag,?R =1.2mag,and ?I =0.8mag.The brightening in R and I was indicated by our ?rst observations at ～JD 2450580,while in B and V it started later at about JD 2450660.These characteristics make the brightening of QW Sge very di?erent from those usually observed for other symbiotic stars -they are signi?cantly pronounced at shorter wavelengths (mainly in U ,see Figs.1,2,7)and also are ?rst detected here.To reveal the origin of the observed brightenings in the QW Sge LCs requires a more detailed study.
3.1
4.IV Vir
The U,B,V measurements of IV Vir (BD-213873)are listed in Table 13.Ob-servations were carried out at the San Pedro Observatory in 2003April at the orbital phase 0.25.The star HD 124991(BD-213877;V =8.072,B ?V =1.048,U ?B =0.730)was used as the comparison.
The brightness of IV Vir is very close to that obtained by us at the orbital phase 0.84(Table 9of S+02).This con?rms the wave variability of this quiet symbiotic,which produces a roughly symmetrical LC.Here,the measurements at phases 0.84and 0.25lie on the descending and the ascending branch of the broad minimum (see Fig.9of S+02).
3.15.V934Her
This peculiar M giant (HD 154791)is the only optical counterpart of a hard X-ray source (4U1700+24)and can be classi?ed as a LMXB (Gaudenzi,Polcaro