- Email: [email protected]
Photometric study of the eclipsing binary IU Aurigae
Chin.Astron.Astrophys.
12 (1988)
298-303
Pergamon
Press
plc.
Printed
in Great
Britain
0275-1062/88$10.00+.00
Act.Astron.Sin. -29 (1988T 138-145
PHOTOMETRIC STUDY OFTHEECLIPSING BINARY IU AURIGAE LIU Xue-fu K.C.
Department of Astronomy, Beijing Normal University
LEUNG, Department of Physics and Astronomy, University of
Nebraska, U.S.A. TAN Hui-song,
Yunnan Observatory, Academia Sinica
ABSTRACT New UBV photometric observations of IU Aur were made at McDonald Observatory in December 1984 and January 1985, showing that the eclipse depth had kept on increasing and the light minimum time had shown periodic changes. Orbital elements were obtained using the Wilson-Devinney method. The inclination is now close to 90’. The continuous variation of inclination over the last few decades suggests the presence of a third body. Absolute parameters of IU Aur were calculated with the help of Mammano’s spectral data.
Received
1.
1987 September
3
INTRODUCTION
IU Aur is a 8 Lyr type eclipsing binary. Its light variability was first discovered in 1962 by Mayer [ll. A number of people have since carried out photoelectric photometry of this object [2-g]. Mayer (1976) discovered periodic variations in the (O-C) of the light minimum time, which he interpreted as due to precession of the orbital plane caused by the perturbation of a third body. Eaton (1978, 1979) observed the binary in the V band and concluded the rate of increase in the orbital inclination to be 0.5’/y. Nearly the same result was obtained by Giuricin (1979, [lo]), who found the rate to be 0.3-0.4&/y. IU Aur is also a two-spectrum Mammano et al. (1969, spectroscopic binary. 1977) made spectral observations. They determined the spectral type to be B 0 p, for the primary, and B 0.5 p for the and found the mass functions to secondary, be 15.3 m, and 10.5m,. Mayer (1965), basing on the observed colour index, found an intrinsic B-V colour index of -0.29, hence deduced a spectral type of B 0.5 for the system. At present, there is still no definite answer to the question whether or not a third body is present, because spectral On the other hand, it evidence is lacking. is of interest to ask: does the eclipse Does the orbital continue to get deeper? inclination continue to increase? And what happens when i is close to 90’? We have
therefore carried out some UBV observations using the Wilson-Devinney method and derived its absolute parameters.
2.
RESULTS OF OBSERVATIONS
Between 1984 December 7 and 1987 January 6, LIU Xue-fu and TAN Hui-song made UBV photoelectric observations of IU Aur using the 91-cm reflector of McDonald Observatory, fitted with a P34B photometer and obtained We took, as useful data on nine nights. comparison star, HD 35619 (SAO 58048), the same star as used by Mayer and Eaton and found no light changes in this star over our To determine the period of observation. magnitude reduction coefficients, we selected suitable nights and observed between 8 and 12 standard stars in the equatorial region and reduced accordingly our observations of IU Aur for atmospheric extinction and magnitude reduction. Fig. 1 shows the UBV light curves. The points are the observations and the continuous curves the theoretical curves from our orbital solution. The two colour curves A (B-V) and A (U-B) are shown in Fig. 2. The observed times of light minimum are given in TABLE 1, where (O-C), refers to Mayer’s (1971) ephemeris formula Min(1)
= JDhel
and (0-C)c
refers
2438448.4076to
the
1.811474E
same author’s
(1) other
IU Aur
formwltr
incorporating -
~.~~~2~~
f45
a pericsdic
f222lE
-i”
term*
zk%
points. In the ca~~ula~iuu~ the following parameters were fixed: the temperature of the primary Tf,, the gravity darkening coefficients .gzr gX% the albedos Al, As, and the limb-darkening coefficients Xl? x2* In accordance with the spectral type being B 0, we put Z’( = 30900 K; following the usual practice For early type stars, we nut gi = g2 = 2.0, and Ai = Ae = 1.0. The limb dsrkeneing coefficients were selected in accordance with aaodel atmospheres 1141, the values for the three colours being 9,33 (U), 0.31 (31, 0,30 (VI, far both xl and q. Adjustable paraaeters were the following: the arbital inclination i, the mass-ratio g = sslml, temperature of the secondary Ts, the potential function Or (or Qa), and the luminosities of the two components 11, lsr and that of the putative third body, is. Of three, the parameter q is the key parameter. For each of a series of Q values (9.2, 0.4, 0.6, 0.8, 1.0, 1.25$ 1,6T, 2.5, 5.01, a ~rellmin~y adjustment was made, result~u~ in an error of fit, IL original
15? (21
The eclipse depths found from the light curves are given in the last column of TABGE 2. The other columns list previous results from other authors. This tabulation shows that the eclipse depth has unbrokenly increased between 1964 and 1985, It appears that s third body is present which causes the orbital plane to precess and the orbital inclination (hence the eclipse depth1 to undergo a steady increese.
We applied the Wilson-Revinse~ metbod I131 to the three-colour UBV light curves of IU Aur for a simultaneous salt&ion of its orbit. First, the observed points ordered along phase were combined into 74 normal points with weights equal to the number of
299
LIO Xue-fuet 81.
300
0.14
PHASE Fig.2 The ColoutindexA(B-V) andA(&B)
Curves of IU AW.
TABJE 1 Times of LightMinimumof 3U hur
6043.92016
TABLE 2 EclipseDepthsof IU Aur
301
IU Aur
Table
3
photometric
Photometric
mode 4
MV>
wu
(LI and Leung)
26838K
25062.0K
(f76.6)
(i-54.7)
tt (pole)
r2 (back) r2 (point) 91
0.3301
(rt.604) 0.218
(~*OO~O~
(f.0032)
0.2972
0.2896
(Ifi.OOSS) 0.3330
(f.0046)
(rfr.0020)
(~.OOlS) 0.3351
0.362
(*.oozs)
(f.0018)
ck.o02>
0.3803
0.3669
(k.0036)
(f.0027)
0.4443
0.4293
(~.0018)
(&.0014)
0.3387
0.3396
(&.0016)
(f.0011)
0.3573
0.3514
0.3516
(f.0042)
(f.0019)
(f.0013)
0.3885
0.3678
(rfi.OOS9)
(jr.0023)
0.4535
0.3537
(k.0029)
(f.0030)
3.7447
‘I.?526
Tl
3.4728
0.339
ck.002)
0.3654 (f.0015) 0.3778 (j;.OOl9) 4.5872
(rfi.0254)
Q2
(&.OO7)
0.3488
0.3885 0.3407
(rt.004) 0.180
0.3204
(f.0057) (rt.0034)
rz (aide)
(f.0032)
0.3384
0.3335
0.3697
8993 (k-3) 27iOOK
(f.ooao)
(f.0045)
0.3513
(11.06) 24857.0K
0.68
(a90) 0.219
Q.3356
0.3382
1.541 89175
(rfi53.3) 0.3369
0.3315
0.2905
lutioo
4
89"75 (it.99)
(j1.0041)
rl (point)
4 1.319
(f1.o4)
(Ifi.0033)
r1 (back)
Leung and Tan)
5 0.833
(k.0028)
rl (side)
general 80
(*.ooSa)
r1 (pale)
sulutionr
(Liu,
(&-.OQ47)
h(U)
of IU Aur
(1984.12-1985.1)
89Z75
l-2
solutions
3.51 ck.01)
4.6612
5.2129
(k.0192)
(f.0157)
30900K
30900K
30900K
fQ.0237
&0.0217
We then selected that value q corresponding to the minimum in the q-C curve (Fig. 31 and entered it in a final adjustment of all the adjustable parameters. Because the spectral data of Mammano et al. (1977) gave q = 0.686, we also made a search for the best Our calculations value around q q 0.6. showed that any of the three values (q = 0.833, 1.319, 1.541) will return a set of elements that will give a good fit to the observed light curves. This shows that
f0.0237
there is non-uniqueness in the photometric solution. Our three solutions are given in TABLE 3, where we have added the recent "general solution" by Li and Leung (1986) based on observations over the past few decades (including the present ones) and a fixed g value (0.68). Apart from q, adjustment of i was also important, for near i = 90’, the residuals become very sensitive to small changes in i. Care should also be exercised in the
LIU Xue-fu
302
Table 4 Absolute Photometric -7
et
Dimens>ons
15
17.4
10
11.8
6.5
7.2
5.0
6.6
6.3
8.5
18.47
18.5
4.490
4.490
log T-2
4.428
4.419
log Ll/I.,
4.540
4.62
log LZJ&
4.309
5. curve
adjustment of the other parameters. It should be pointed out that the calculated luminosity of the third body was as much as 23% of the total luminosit,y, which is by no means negligible, indicating that a third body is indeed present. Fig. 4 illustrates the semi-detached configuration of IU Aur, as seen at phase 0.25. 4.
ABSOLUTE
PARAMETERS
Combining the above orbital elements the spectrai data of Mammano et al., derived systems,
the
absolute
parameters
of
with we the
namely, the masses, radii and luminosities of the two components and their FCItdistance apart, .+l, shown in TABLE 4.
comparison, results also included.
by other
authors
0.687
O.G8
Fig.
The residual-q
00) (B0.5)
4.20
_-
o.s33
4
are
etc.
(1977)
10.5
log Tl
3
Mammano
15.3
_-
Fig.
Spectral
Li and LCUUg (1986)
_-
..-
of IU Aur
general
_-
this paper
ml (mm) m2 (mo> RI (Jb) R2 UGd R (Ret’
al.
4
IO Aur at phase
0.25
CONCLUSION
IU Aur is a Beta Lyrae type eclipsing binary. It is a semi-detached system, its less massive component filling its Rochc lobe, Our photoelectric observations showed that its eclipse depth continued to increase, and so did its orbital inclination, now nearly 90”. Periodic variation in the light minimum time does indeed exist, i.e., the light-time effect. Photometric solutions give a non-negligible luminosity of a third body, showing that the system is very probably a triple system. The perturbation by the third body would cause the orbital plane to precess, the orbital inclination to change and the eclipse depth to increase. Spectral evidence for a third body is still lacking, hence further observational confirmation is awaited, Three photometric solutions were found that gave good fit to the observations, showing the non-uniqueness of the solution. Also the difference between the photometric and spectroscopic solutions should be
IU Am-
studied various
further. solutions
However, the absolute are nearly the same.
303
parameters
derived
from the
REFERENCES
r 11
Mayer, P., Publ. Arrron. Sot. Pacific, 77(1965),
121
Rossrti,
F., Men. Sot. Asw. P., Bull.
Arrron. Inst. Czechorlovo~io. 22( 1971),
131
Mayer,
141
Mayer, P. Reprinted from
r51
Mayer,
r61
Eaton,
J. A., Ap. I.,
[71
Eaton,
J. A., A. I., J.
197(1975), 28(1978),
Eaton,
Pettersen,
IlO1
Giuricin,
r111
Mammano,
A. Margoni.
1121
Mammano,
A. Margoni,
G., Mardirossian,
rw
Wilson,
R. E. and
Carbon,
D. F. and
Gingerich,
0.
168. institutes
of czechorlovakia,
27(1976).
5, 308.
379.
63.
B. R., Ap. 80(1979),
1’41
of the astronomical
Bull. Var. Szars, 1979,
la1 r91
Inf.
the Bulletin
T., Inf. Bull. Var. Srorr, 1983, No. 2407.
P. and Jozef,
A.,
436.
1~1.. 38( 1967), 743.
F.. Mezzetti, R. and R. and
Devinney, Cingerich,
(Cambridge:
No.
1614.
265. Stagni. Strgni,
M. and Cester, B. A. Ap. Supple. 37(1979), 513. R., 1969 Bibl. and Prag. Note1 on Eel. Vu No. R., A. Ap,
E. J., Ap. I., 0..
MIT
166(1971),
1969, in Theory Press).
59(1977), and
15.
9.
605. Observations
of Normal
Stellar
Atmospheres,
cd.
12 (1988)
298-303
Pergamon
Press
plc.
Printed
in Great
Britain
0275-1062/88$10.00+.00
Act.Astron.Sin. -29 (1988T 138-145
PHOTOMETRIC STUDY OFTHEECLIPSING BINARY IU AURIGAE LIU Xue-fu K.C.
Department of Astronomy, Beijing Normal University
LEUNG, Department of Physics and Astronomy, University of
Nebraska, U.S.A. TAN Hui-song,
Yunnan Observatory, Academia Sinica
ABSTRACT New UBV photometric observations of IU Aur were made at McDonald Observatory in December 1984 and January 1985, showing that the eclipse depth had kept on increasing and the light minimum time had shown periodic changes. Orbital elements were obtained using the Wilson-Devinney method. The inclination is now close to 90’. The continuous variation of inclination over the last few decades suggests the presence of a third body. Absolute parameters of IU Aur were calculated with the help of Mammano’s spectral data.
Received
1.
1987 September
3
INTRODUCTION
IU Aur is a 8 Lyr type eclipsing binary. Its light variability was first discovered in 1962 by Mayer [ll. A number of people have since carried out photoelectric photometry of this object [2-g]. Mayer (1976) discovered periodic variations in the (O-C) of the light minimum time, which he interpreted as due to precession of the orbital plane caused by the perturbation of a third body. Eaton (1978, 1979) observed the binary in the V band and concluded the rate of increase in the orbital inclination to be 0.5’/y. Nearly the same result was obtained by Giuricin (1979, [lo]), who found the rate to be 0.3-0.4&/y. IU Aur is also a two-spectrum Mammano et al. (1969, spectroscopic binary. 1977) made spectral observations. They determined the spectral type to be B 0 p, for the primary, and B 0.5 p for the and found the mass functions to secondary, be 15.3 m, and 10.5m,. Mayer (1965), basing on the observed colour index, found an intrinsic B-V colour index of -0.29, hence deduced a spectral type of B 0.5 for the system. At present, there is still no definite answer to the question whether or not a third body is present, because spectral On the other hand, it evidence is lacking. is of interest to ask: does the eclipse Does the orbital continue to get deeper? inclination continue to increase? And what happens when i is close to 90’? We have
therefore carried out some UBV observations using the Wilson-Devinney method and derived its absolute parameters.
2.
RESULTS OF OBSERVATIONS
Between 1984 December 7 and 1987 January 6, LIU Xue-fu and TAN Hui-song made UBV photoelectric observations of IU Aur using the 91-cm reflector of McDonald Observatory, fitted with a P34B photometer and obtained We took, as useful data on nine nights. comparison star, HD 35619 (SAO 58048), the same star as used by Mayer and Eaton and found no light changes in this star over our To determine the period of observation. magnitude reduction coefficients, we selected suitable nights and observed between 8 and 12 standard stars in the equatorial region and reduced accordingly our observations of IU Aur for atmospheric extinction and magnitude reduction. Fig. 1 shows the UBV light curves. The points are the observations and the continuous curves the theoretical curves from our orbital solution. The two colour curves A (B-V) and A (U-B) are shown in Fig. 2. The observed times of light minimum are given in TABLE 1, where (O-C), refers to Mayer’s (1971) ephemeris formula Min(1)
= JDhel
and (0-C)c
refers
2438448.4076to
the
1.811474E
same author’s
(1) other
IU Aur
formwltr
incorporating -
~.~~~2~~
f45
a pericsdic
f222lE
-i”
term*
zk%
points. In the ca~~ula~iuu~ the following parameters were fixed: the temperature of the primary Tf,, the gravity darkening coefficients .gzr gX% the albedos Al, As, and the limb-darkening coefficients Xl? x2* In accordance with the spectral type being B 0, we put Z’( = 30900 K; following the usual practice For early type stars, we nut gi = g2 = 2.0, and Ai = Ae = 1.0. The limb dsrkeneing coefficients were selected in accordance with aaodel atmospheres 1141, the values for the three colours being 9,33 (U), 0.31 (31, 0,30 (VI, far both xl and q. Adjustable paraaeters were the following: the arbital inclination i, the mass-ratio g = sslml, temperature of the secondary Ts, the potential function Or (or Qa), and the luminosities of the two components 11, lsr and that of the putative third body, is. Of three, the parameter q is the key parameter. For each of a series of Q values (9.2, 0.4, 0.6, 0.8, 1.0, 1.25$ 1,6T, 2.5, 5.01, a ~rellmin~y adjustment was made, result~u~ in an error of fit, IL original
15? (21
The eclipse depths found from the light curves are given in the last column of TABGE 2. The other columns list previous results from other authors. This tabulation shows that the eclipse depth has unbrokenly increased between 1964 and 1985, It appears that s third body is present which causes the orbital plane to precess and the orbital inclination (hence the eclipse depth1 to undergo a steady increese.
We applied the Wilson-Revinse~ metbod I131 to the three-colour UBV light curves of IU Aur for a simultaneous salt&ion of its orbit. First, the observed points ordered along phase were combined into 74 normal points with weights equal to the number of
299
LIO Xue-fuet 81.
300
0.14
PHASE Fig.2 The ColoutindexA(B-V) andA(&B)
Curves of IU AW.
TABJE 1 Times of LightMinimumof 3U hur
6043.92016
TABLE 2 EclipseDepthsof IU Aur
301
IU Aur
Table
3
photometric
Photometric
mode 4
MV>
wu
(LI and Leung)
26838K
25062.0K
(f76.6)
(i-54.7)
tt (pole)
r2 (back) r2 (point) 91
0.3301
(rt.604) 0.218
(~*OO~O~
(f.0032)
0.2972
0.2896
(Ifi.OOSS) 0.3330
(f.0046)
(rfr.0020)
(~.OOlS) 0.3351
0.362
(*.oozs)
(f.0018)
ck.o02>
0.3803
0.3669
(k.0036)
(f.0027)
0.4443
0.4293
(~.0018)
(&.0014)
0.3387
0.3396
(&.0016)
(f.0011)
0.3573
0.3514
0.3516
(f.0042)
(f.0019)
(f.0013)
0.3885
0.3678
(rfi.OOS9)
(jr.0023)
0.4535
0.3537
(k.0029)
(f.0030)
3.7447
‘I.?526
Tl
3.4728
0.339
ck.002)
0.3654 (f.0015) 0.3778 (j;.OOl9) 4.5872
(rfi.0254)
Q2
(&.OO7)
0.3488
0.3885 0.3407
(rt.004) 0.180
0.3204
(f.0057) (rt.0034)
rz (aide)
(f.0032)
0.3384
0.3335
0.3697
8993 (k-3) 27iOOK
(f.ooao)
(f.0045)
0.3513
(11.06) 24857.0K
0.68
(a90) 0.219
Q.3356
0.3382
1.541 89175
(rfi53.3) 0.3369
0.3315
0.2905
lutioo
4
89"75 (it.99)
(j1.0041)
rl (point)
4 1.319
(f1.o4)
(Ifi.0033)
r1 (back)
Leung and Tan)
5 0.833
(k.0028)
rl (side)
general 80
(*.ooSa)
r1 (pale)
sulutionr
(Liu,
(&-.OQ47)
h(U)
of IU Aur
(1984.12-1985.1)
89Z75
l-2
solutions
3.51 ck.01)
4.6612
5.2129
(k.0192)
(f.0157)
30900K
30900K
30900K
fQ.0237
&0.0217
We then selected that value q corresponding to the minimum in the q-C curve (Fig. 31 and entered it in a final adjustment of all the adjustable parameters. Because the spectral data of Mammano et al. (1977) gave q = 0.686, we also made a search for the best Our calculations value around q q 0.6. showed that any of the three values (q = 0.833, 1.319, 1.541) will return a set of elements that will give a good fit to the observed light curves. This shows that
f0.0237
there is non-uniqueness in the photometric solution. Our three solutions are given in TABLE 3, where we have added the recent "general solution" by Li and Leung (1986) based on observations over the past few decades (including the present ones) and a fixed g value (0.68). Apart from q, adjustment of i was also important, for near i = 90’, the residuals become very sensitive to small changes in i. Care should also be exercised in the
LIU Xue-fu
302
Table 4 Absolute Photometric -7
et
Dimens>ons
15
17.4
10
11.8
6.5
7.2
5.0
6.6
6.3
8.5
18.47
18.5
4.490
4.490
log T-2
4.428
4.419
log Ll/I.,
4.540
4.62
log LZJ&
4.309
5. curve
adjustment of the other parameters. It should be pointed out that the calculated luminosity of the third body was as much as 23% of the total luminosit,y, which is by no means negligible, indicating that a third body is indeed present. Fig. 4 illustrates the semi-detached configuration of IU Aur, as seen at phase 0.25. 4.
ABSOLUTE
PARAMETERS
Combining the above orbital elements the spectrai data of Mammano et al., derived systems,
the
absolute
parameters
of
with we the
namely, the masses, radii and luminosities of the two components and their FCItdistance apart, .+l, shown in TABLE 4.
comparison, results also included.
by other
authors
0.687
O.G8
Fig.
The residual-q
00) (B0.5)
4.20
_-
o.s33
4
are
etc.
(1977)
10.5
log Tl
3
Mammano
15.3
_-
Fig.
Spectral
Li and LCUUg (1986)
_-
..-
of IU Aur
general
_-
this paper
ml (mm) m2 (mo> RI (Jb) R2 UGd R (Ret’
al.
4
IO Aur at phase
0.25
CONCLUSION
IU Aur is a Beta Lyrae type eclipsing binary. It is a semi-detached system, its less massive component filling its Rochc lobe, Our photoelectric observations showed that its eclipse depth continued to increase, and so did its orbital inclination, now nearly 90”. Periodic variation in the light minimum time does indeed exist, i.e., the light-time effect. Photometric solutions give a non-negligible luminosity of a third body, showing that the system is very probably a triple system. The perturbation by the third body would cause the orbital plane to precess, the orbital inclination to change and the eclipse depth to increase. Spectral evidence for a third body is still lacking, hence further observational confirmation is awaited, Three photometric solutions were found that gave good fit to the observations, showing the non-uniqueness of the solution. Also the difference between the photometric and spectroscopic solutions should be
IU Am-
studied various
further. solutions
However, the absolute are nearly the same.
303
parameters
derived
from the
REFERENCES
r 11
Mayer, P., Publ. Arrron. Sot. Pacific, 77(1965),
121
Rossrti,
F., Men. Sot. Asw. P., Bull.
Arrron. Inst. Czechorlovo~io. 22( 1971),
131
Mayer,
141
Mayer, P. Reprinted from
r51
Mayer,
r61
Eaton,
J. A., Ap. I.,
[71
Eaton,
J. A., A. I., J.
197(1975), 28(1978),
Eaton,
Pettersen,
IlO1
Giuricin,
r111
Mammano,
A. Margoni.
1121
Mammano,
A. Margoni,
G., Mardirossian,
rw
Wilson,
R. E. and
Carbon,
D. F. and
Gingerich,
0.
168. institutes
of czechorlovakia,
27(1976).
5, 308.
379.
63.
B. R., Ap. 80(1979),
1’41
of the astronomical
Bull. Var. Szars, 1979,
la1 r91
Inf.
the Bulletin
T., Inf. Bull. Var. Srorr, 1983, No. 2407.
P. and Jozef,
A.,
436.
1~1.. 38( 1967), 743.
F.. Mezzetti, R. and R. and
Devinney, Cingerich,
(Cambridge:
No.
1614.
265. Stagni. Strgni,
M. and Cester, B. A. Ap. Supple. 37(1979), 513. R., 1969 Bibl. and Prag. Note1 on Eel. Vu No. R., A. Ap,
E. J., Ap. I., 0..
MIT
166(1971),
1969, in Theory Press).
59(1977), and
15.
9.
605. Observations
of Normal
Stellar
Atmospheres,
cd.