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Photoelectric photometry of the early-type semi - detached binary UW orionis
Chin.Astron.Astrophys.(1990114/3,298-305 9 Pergamon Press plc A translation of Printed in Great Britain Acta Astron.Sin.(1990131/1,7-14 0275-1062/90$10.00t.00
PHUTOELEKTRIC PHOTOMETRY OFTHEEARLY-TYPE SEMI-DETACHED BINARY DWORIONIS ZBANG Rong-xian ZHAI Di-sheng ZBANG Ji-tong ZBANG Xiao-yu LI ei-sheng Beijing Astronomical Observatory, Chinese
Academy
of Sciences
Received 1989 January 10
ABSTRACT liegive a photoelectric light curve of UW Ori for the first time and a new epoch formula. A preliminary photometric solution was obtained using the Wilson-Devinney method of light curve synthesis. The reuslts show that it is an early-type, almost contact, semi-detachedbinary of large mass, with a mass ratio 0.513. If the large mass component is a eero age main sequence star, then the small mass component is no longer such. The O-C in the time of minimum suggest a possibly increasing period.
Key words: Eclipsing binaries--early-typesemi-detached binaries-photometric solution
1. INTRODUCTION UW Ori is an eclipsing binary of spectral type B. It is located near the Mira variable U Ori. A first series of visual minimum times was given by Lecher in 1911 [ll, together with an epoch formula, but the period given was not correct. In 1957, Whitney 121 gave 8 photographic minimum times and further photographic observations were made by Ahnert [3] and Zinner [4]; but photoelectric data have been lacking for a long time. Because UW Ori has a short period (about 2 days), an early type spectrum and a p Lyrae type of light curve, it is probably a contact or semi-detached system. Hence it was included in the Beijing Observatory sutdy project on near-contact eclipsing binaries.
2. OBSERVATION We used the 60 cm reflector at Xinglong Station, Beijing Observatory and a single channel photometer and carried out two-colour photoelectric photometry of W Ori during two observing periods, 1986 October-1987 February and 1987 October-1988 January. Effective observations were made on 18 nights and 567 observing points in both B and.V bands were obtained. In addition, UBV three-colour measurements were made outaide the eclipses and three times of
UWOrionis
299
light minimum were detersined. The position, of IJWOri, the comparison and control stars TABLE1
magnitude and coloura are given in TABLE1,
Position aud Magnitudes of UWOri, and of the Comparison and Control Stars Q(1987)
6 (1987)
05’55=07”
20*&0’07”
fll~S2fO&4
O’DSSfO,O4
-0?45&fLO5
ni 54 %I
at OI I2
111.9,
0.33
--o.Sb
OS 55 us
20 07 12
*Values of UBVouteide
eclipse
B-V
V
9.05&0.02
U-B
0.e3j;o.o
near main saximua
The nightly
first-order extinction coefficients and manthly average second-order coefficients were used. The observations were reduced to the international UBV system The standard stars used were secondary standards and the rms errors of the comparison and control stare were ail less than *1.5X, in both B and V. 3, LIGHTCURVEAER EPOCHFORHULA The B and V light data of the light
curves of UW Ori are shown in Fig. 1. Nuaerioal curves are given in TABLE2. The light curves are
1 o.*
02
0.4
0.0
0.0
Ml
phase
Fig. 1 The light curves of tJWOri in B and V bauda. Crosses are observations in 1986,10-1987.1, circles1 in 1987.12-1988.1
300
ZHAWG Bong-xian et al.
p Lyr type, the depth of the main eclipse is 0.54mag, that of the secondary eclipse, 0.54 nag. The light curves are basically symmetrical with no obvious distortions.
of
TABLE 2 solovr II
V
Ma1.11
Min.ll
II?04 IO.51
II?04 IU.51
II?58 11.05
TABLE 3 NO. I 2 3
4 ¶ 6 7 8 9 IO 11 12 13 I4 IS 16 17 I8 19 20 21 12 23 14 25 26 27
Characteristicsof the Light Curves
Ml1.I
T.
o-c
143u7d4730 16172.3240 16871.3910 17198.5130 17239.2430 17242.3420 17297.3880 17614.3040 17668.3340 17670.3930 18264.4570 18361.2970 19013.44so
-16125.0 -15210.0 '-14867.0 -14706.1 -14688.1 -14685.0 -~14618.0 -14SOZ.S -14476.0 --14479.11 -1418J.S -14136.0 -138l6.tl I9058.274ll . I17'll.II 19068.5020 -13789.0 33657.4500 -6631.0 31428.9480 -5762.0 33432.6220 -5760.0 35483.6140 -3735.0 31808.6800 --5171.5 .~WIII.57~0 >5:3.5 .ibLH7.b130 5(iO.% .JbllH.b??ll s207.t 46794.2144 47172.2861 47173.2917
or54 0.54
Times of Light Minimum of UW Ori E
Jb391.74IO
OF'76 0.76
0?0367 -0.0004 -0.0117 -0.0095 0.0342 -0.0002 0.0163 0.0032 0.0228 0.0037 -0.0070 0.0219 -6.0314 . U.IMII
W
method
1.0
PK.
I.0
PK.
1.0 I.0 I.0 I.0 I.0 I.0 I.0 I.0 1.0 1.0 I.0 I.0 I.0 1.0 1.0 I.0 1.0 I.0 I.11
PC. pt. PC.
,,.,,?I"
I.0
PI.
0.Il.WII
I.0
PI.
5llll,.ll . II.IIL7: -183.5 0.0189 0.0177 0.0 0.0042 0.5
I.0 2.0 2.0 2.0
PI.
-0.0039 O.OlSB -0.0204 -0.0227 0.0161 11.0005 1I.11, 111
PI.
PI. PK. PC, P!. PC. 91. PI. PI. PI. PK. PI. PC. PC. PI. rr.
PI. PS. PC.
t hj this . paper this
paper
We measured a total of three light minimum times, determined using the K-W method. The following values for the period are found in the literature: 0d.407902 [I], 2d.038127 [5], 2d.038101 161, ld.0080525 [7]. From the minimum times we collected and referring to the second of our observed times as eero, a least squares solution gave the first degree and second degree epoch formulae as follows: JD Hel(Min.1)
-
2447172?2684 + 2?03812913 X E. f
50
47
(1)
UW Orionis
JD Hel(Min.l)
-
301
2447172?2829 + 2:‘0381371 X E + 4.96 X IO-” X E’. 18
54
f
(21
1.10
In the calculation we found four points with O-C as much as 0.1-0.9 d, which seemed to be caused by outstanding errors. These were discarded in Whitney’s paper, and so we followed the practice. Photoelectric minimum times were given weight 2 and other tines, weight 1. From epoch formula (2) we have AP/P
= 4.87
x lo-lo
= 1.51 x lo+
s/yr,
showing that the period has a tendency to increase slowly. As may be seen from the O-C diagram in Fig. 2, most of the points come from visual and photographic observations and there is a large scatter, hence this tendency can only be regarded as a possibility at the present and should be confirmed with further photoelectric measurements. (0-C)”
;jj
- 10000
.-1400u
Fig. 2 O-C diagram of the minimum times of UW Ori. Only our 3 measurements (triangles) were photoelectric, the others (crosses) were all photographic or visual.,
TABLE 4a inc.
Normal Points
of the V Light
Curve
ior.
N
N
0.0143
0.1699
2
0.4716
0.2469
0.0212
0.1973
2
0.4787
0.2347
3
0.0269
0.2113
2
U.4834
0.2292
2
0.0341
0.2242
3
0.4997
0.1256
7
0.0439
0.2364
3
O.%lOO
0.2295
5
0.0677
0.1769
3
11.520~1
0.24116
2
0.0774
,I.:"~?5
z
11.554ll
u.27u5
2
0.0901
0.3IOll
4
0.S56.6
0.2665
1
0.1216
0.3425
7
0.5651
0.2965
3
0.1432
0.3106
7
0.5757
0.3072
3
0.1619
0.3603
7
0.5693
0.3224
6
0.1966
0.3660
I.7
0.6061
0.3365
5
0.2312
0.3736
R
0.6561
0.3620
7
0.2554
9.3764
9
0.675s
0.3660
2
0.2772
0.3729
II
0.6944
0.3722
7
0.3297
0.3632
II)
0.7315
0.3772
7
0.3701
0.3509
7
0.7677
0,371o
3
0.3600
0.3434
5
0.7972
0.3691
I6
6
302
ZHANG Rong-xian et al.
TABLE 4a (contd.) phase
int.
0.3905
0.3302
0.4050 0.4180
inr.
N
U.8422
0.3576
24
0.32111
0.8800
0.3434
9
0.3164
0.9013
0.3269
6
0.4272
0.3us7
0.91411
0.3100
6
0.4341
0.2945
0.9344
0.2Y13
33 9
PhW
0.4437
0.2799
0.9536
0.2464
0.4524
11.2t,9(1
U.9‘61
II.ZLJ"
9
0.4621
n.25Y2
".99,X
O.IRRI
6
TABLE 4b
Nomal Points of the B Light Curve
,111.
N
yhrre
,I,,.
N
0.0146
0.2912
2
0.4416
0.4453
6
0.0216
0.3102
2
0.4533
0.4272
7
0.0258
Il.3230
0.4684
0.3934
9
11."29(1
I,.,,,,,
,1.47'>,1
II.(76"
4
U.U.(611
11.,5117
I ? L
,1.49,,,
0. IDIJ
5
0.0443
0.3712
3
0.5065
U.3607
6
0.0640
0.4355
2
0.5201
0.31142
2
0.0719
0.4487
3
0.5572
0.4461
4
0.01117
0.4759
2
0.5601
0.4662
3
0.0926
0.4949
3
0.5791
0.4876
4
0.1310
n.54In
8
0.5966
0.5173
6
0.14118
Il.5517
5
lJ.61UY
0.5356
3
0.1641
0.5615
.4
0.6697
0.5703
9
0.1831
11.5711
?
0.7039
0.5820
6
0.2072
0.5835
R
0.7307
0.58311
0.2386
n.5Y93
16
0.7550
0.5876
0.2696
n.5Y71
8
0.7971
0.5778
18
0.2841
0.5055
6
0.Y420
0.5595
27
0.3on1
0.576'1
24
n.879Y
(I.5318
9
0.3296
0.5684
18
0.9011
0.5076
6
0.54')(
39
0.9146
Il.4819
6
U.5,,',
6
,,.',,-,.I
~I.4371
33
0.3126
u.53lJ7
1u
O.Y536
0.3863
9
0.3996
0.516,
6
0.9672
0.3442
9
0.4152
0.4942
9
0.9934
0.2912
6
0.4297
0.4729
7
:0.3618 0.36Yll
7 18
4. PHOTOMETRIC SOLUTION First, the observations were grouped into normal points according to the epoch formula (1). There were 52 normal points in the V curve (TABLE 4a) and 51 in the B curve (TABLE 4b). We used the well-known Wilson-Devinneymethod of light curve synthesis to solve for the orbit. The main part of the light curve used comes from the 1986.10-1987.1 season, part of the phase (0.0-0.1 and 0.5-0.6) uses the 1987.10-1988.1observations.The spectral type of the star is B, its subclass was not known. For
UK Orionis
303
this, we used our outside eclipse UBV measurements, applied extinction correction and, UWOri being located on the galactic plane, we corrected for reddening using Crawford’s method [El, then with reference to Popper’s results [El we found the spectral type to be Bl. This is further checked with the UBV measurements of the comparison star, for which the spectral type is known. Hence we adopted the spectral type of the main star (Component 1)‘ of IJUOri to be Bl, with an effective surface temperature of 25400°K. We assumed the thermal albedo and gravity darkening coefficients to be 1.0 for both components and the x U.Wl,limb darkening coefficient to be ‘7 0.25 in V and-O.30 in B. We began by assuming a detached model, but 0.015 we found Component 2 converging . towards the critical surface during the iteration, so we changed to a 0.014 semi-detached model. From the residual-mass ratio diagram (Pig. 3) we see that the residual ; is the least at q =0.513. The o:'L L." Q corresponding photometric solution is as given in TABLE 5. The results Fig. 3 show that Component 1 is the more massive component. The coefficients A, q and x were fixed rather than adjustable because the spectral type was probably uncertain by one subclass and different phase intervals were observed at rather different times.
I
+J
I .,. +-----
Y
TABLE 6
Photometric
COlOr
w(L,+L,)
”
--___
=*
of UU Ori B45UOA
0.668*0.001
0.686*0.001
0.25'
0.30.
f, _____-..~
Eolution
5suux
lJ.25*
._.
I
0.30. 86:39*0:14 0.r13~0.014
4=Wm, corn,'.I
--~_____9
1.U'
A
1.1).
Tn~
254UO'
0
comp.2 1.0* 1.U' 21169*60
3.U667f0.0071
2.9011**
r(PUle)
0.3864~0.0013
0.301S~0.0006
r(poinc)
0.4536~0.0022
0.4319-+0.0008
r(ride)
'l.4054~0.0016
u.31s1*0.0007
r(back)
0.4252~0.0021
Qt..
*assuraed
I **theoretical
0.3475*0.0007 2.9OII**
value
5. SBSULTS ANDDISCUSSION From
almost
the preliminary solution contact, semi-detached
we see that UK Ori is an early-type, binary where the main component is of
304
ZHANG Bong-xian
et al.
spectral type Bl and the secondary, B2. The secondary is the less massive one, it fills its critical surface while the main, more massive star nearly does so, with a degree of contact, r,/rl(Q,t,) q 0.93, very similar to TX Cas (101. Because there are no radial velocity measurements, we cannot derive the absolute parameters of the binary, but we can use the method described by ZHAI Di-sheng et al. 1111 and discuss the evolution of the system on the basis of the relative parameters given by the photometric solution. Recently, ZHAI Di-sheng et al. [12] used the absolute parameters of 171 components belonging to ‘88 two-spectrum detached binaries and re-calibrated the empirical ZAM8 (zero-age main sequence)
mass-radius relation. This had a gradient of a = 0.642 in the log R-1ogW diagram for spectral types between 09 and F6. If both components are ZAMS stars, then we should have log(Rz/Rl)/log(Mz/M,) = 0.642. The left side can be expressed in terms of the relative parameters as log(rz/rl)/logq, and this is equal to 0.38 from our solution. This is clearly less than the above value of 0.642. If we assume the more massive comnonent is on the ZAM8, then the less massive one has clearly evolved-out of it; if ml itself has already evolved to some extent, then ms will have evolved to an even greater extent. -1 This is consistent with our finding me filling its Roche lobe (see Fig. 4), that is, UW Ori belongs to the Algol type of semi-detached binary in which the me is the component that is losing mass. If -_.._the suggestion that the period is increasing turns out to be true, then it will be probable that ~712is Fig. 4 continuing losing matter to ml. If we assume ml to be still on the main sequence, then from the mass-spectrum relation we can find its mass to be about 13 &, hence we derive a radius of ~6.4 b, and for m2, ~6.7 & and -5.Ok. Then on the mass-radius diagram [12], m2 will still be within the main seqeunce band. Hence UW Ori is probably a product of Case A mass exchange. By means of Mochnacki’s formula parameters given by the present
[13], we can use the relative solution to calculate the mean
densities of the two components and we find the ratio &/& = 0.92, quite close to 1, so m2 indeed has not undergone much expansion and this is consistent exchange.
with the above deduction
of Case A mass
Thus, UW Ori is a new almost contact semi-detached binary. Analysing its features will undoubtedly contribute to the study of the evolution of binaries with non-constant mass exchange. Because the spectral type was not directly observed, we repeated the calculation assuming the spectral type of ml to be B5 or B9. We found that, as the assumed spectral type gets later, q increases (to nearly 1 at B9), but the configuration is not greatly changed,
UU Orionis
305
m2 still fills its Roche lobe while the degree of contact of ml changes slightly. For better determinations of the absolute parameters of the system, spectroscopic observations are very necessary.
REFERENCES [ll Lecher, W., AN 187 (1911), 191. 64 (1959), 258. [21 Whitney, S., A.J., r31 Ahnert, P., Mitteilungen uber veranderliche sterne, Berlin-Babelsbergund Sonnenberg No.643. [41 Zinner, S., Veroffentlichungender Remeis-Sternwarte,Bamberg. 1, 3. t51 Wood, F.B. et al., A finding list for observers of interacting binary stars, 1980. (61 Banachiewice, T., Rocenik astronomiceny obserwatorium Krakowskiego Nr. 58 (1987). (71 Kukarkin, B., Gen. Catalogue of Variable Stars, Moscow, 1970, 1986. 88 (1976), 917. (81 Crowford, D.L., PASP., ~. [91 Popper,D.M., Ann. Rev. Astton. Astrophys. 18(1980), 115. [lOI ZHAI Di-sheng, ZHANG Rong-xian, ZHANG Ji-tong and LI Qi-sheng, Chin.Astron.Astrophys.12/1(1988)60-69. =ActaAstron.Sin. 28/l (1987) 71-81. 1111 ZHAI Di-sheng, LEUNG K.C., ZHANG Rong-xian and ZHANG Ji-tong, Chin.Astron.Astrophys. 9/2 (1985) 139-144. = Acta 5/l (1985) 26-35. (12) Zhai, D.S. and ZhangX.Y., Publ. BAO., 12 (1989) 113) Mocnacki, S.W., Ap. J. 245 (1981), 650
PHUTOELEKTRIC PHOTOMETRY OFTHEEARLY-TYPE SEMI-DETACHED BINARY DWORIONIS ZBANG Rong-xian ZHAI Di-sheng ZBANG Ji-tong ZBANG Xiao-yu LI ei-sheng Beijing Astronomical Observatory, Chinese
Academy
of Sciences
Received 1989 January 10
ABSTRACT liegive a photoelectric light curve of UW Ori for the first time and a new epoch formula. A preliminary photometric solution was obtained using the Wilson-Devinney method of light curve synthesis. The reuslts show that it is an early-type, almost contact, semi-detachedbinary of large mass, with a mass ratio 0.513. If the large mass component is a eero age main sequence star, then the small mass component is no longer such. The O-C in the time of minimum suggest a possibly increasing period.
Key words: Eclipsing binaries--early-typesemi-detached binaries-photometric solution
1. INTRODUCTION UW Ori is an eclipsing binary of spectral type B. It is located near the Mira variable U Ori. A first series of visual minimum times was given by Lecher in 1911 [ll, together with an epoch formula, but the period given was not correct. In 1957, Whitney 121 gave 8 photographic minimum times and further photographic observations were made by Ahnert [3] and Zinner [4]; but photoelectric data have been lacking for a long time. Because UW Ori has a short period (about 2 days), an early type spectrum and a p Lyrae type of light curve, it is probably a contact or semi-detached system. Hence it was included in the Beijing Observatory sutdy project on near-contact eclipsing binaries.
2. OBSERVATION We used the 60 cm reflector at Xinglong Station, Beijing Observatory and a single channel photometer and carried out two-colour photoelectric photometry of W Ori during two observing periods, 1986 October-1987 February and 1987 October-1988 January. Effective observations were made on 18 nights and 567 observing points in both B and.V bands were obtained. In addition, UBV three-colour measurements were made outaide the eclipses and three times of
UWOrionis
299
light minimum were detersined. The position, of IJWOri, the comparison and control stars TABLE1
magnitude and coloura are given in TABLE1,
Position aud Magnitudes of UWOri, and of the Comparison and Control Stars Q(1987)
6 (1987)
05’55=07”
20*&0’07”
fll~S2fO&4
O’DSSfO,O4
-0?45&fLO5
ni 54 %I
at OI I2
111.9,
0.33
--o.Sb
OS 55 us
20 07 12
*Values of UBVouteide
eclipse
B-V
V
9.05&0.02
U-B
0.e3j;o.o
near main saximua
The nightly
first-order extinction coefficients and manthly average second-order coefficients were used. The observations were reduced to the international UBV system The standard stars used were secondary standards and the rms errors of the comparison and control stare were ail less than *1.5X, in both B and V. 3, LIGHTCURVEAER EPOCHFORHULA The B and V light data of the light
curves of UW Ori are shown in Fig. 1. Nuaerioal curves are given in TABLE2. The light curves are
1 o.*
02
0.4
0.0
0.0
Ml
phase
Fig. 1 The light curves of tJWOri in B and V bauda. Crosses are observations in 1986,10-1987.1, circles1 in 1987.12-1988.1
300
ZHAWG Bong-xian et al.
p Lyr type, the depth of the main eclipse is 0.54mag, that of the secondary eclipse, 0.54 nag. The light curves are basically symmetrical with no obvious distortions.
of
TABLE 2 solovr II
V
Ma1.11
Min.ll
II?04 IO.51
II?04 IU.51
II?58 11.05
TABLE 3 NO. I 2 3
4 ¶ 6 7 8 9 IO 11 12 13 I4 IS 16 17 I8 19 20 21 12 23 14 25 26 27
Characteristicsof the Light Curves
Ml1.I
T.
o-c
143u7d4730 16172.3240 16871.3910 17198.5130 17239.2430 17242.3420 17297.3880 17614.3040 17668.3340 17670.3930 18264.4570 18361.2970 19013.44so
-16125.0 -15210.0 '-14867.0 -14706.1 -14688.1 -14685.0 -~14618.0 -14SOZ.S -14476.0 --14479.11 -1418J.S -14136.0 -138l6.tl I9058.274ll . I17'll.II 19068.5020 -13789.0 33657.4500 -6631.0 31428.9480 -5762.0 33432.6220 -5760.0 35483.6140 -3735.0 31808.6800 --5171.5 .~WIII.57~0 >5:3.5 .ibLH7.b130 5(iO.% .JbllH.b??ll s207.t 46794.2144 47172.2861 47173.2917
or54 0.54
Times of Light Minimum of UW Ori E
Jb391.74IO
OF'76 0.76
0?0367 -0.0004 -0.0117 -0.0095 0.0342 -0.0002 0.0163 0.0032 0.0228 0.0037 -0.0070 0.0219 -6.0314 . U.IMII
W
method
1.0
PK.
I.0
PK.
1.0 I.0 I.0 I.0 I.0 I.0 I.0 I.0 1.0 1.0 I.0 I.0 I.0 1.0 1.0 I.0 1.0 I.0 I.11
PC. pt. PC.
,,.,,?I"
I.0
PI.
0.Il.WII
I.0
PI.
5llll,.ll . II.IIL7: -183.5 0.0189 0.0177 0.0 0.0042 0.5
I.0 2.0 2.0 2.0
PI.
-0.0039 O.OlSB -0.0204 -0.0227 0.0161 11.0005 1I.11, 111
PI.
PI. PK. PC, P!. PC. 91. PI. PI. PI. PK. PI. PC. PC. PI. rr.
PI. PS. PC.
t hj this . paper this
paper
We measured a total of three light minimum times, determined using the K-W method. The following values for the period are found in the literature: 0d.407902 [I], 2d.038127 [5], 2d.038101 161, ld.0080525 [7]. From the minimum times we collected and referring to the second of our observed times as eero, a least squares solution gave the first degree and second degree epoch formulae as follows: JD Hel(Min.1)
-
2447172?2684 + 2?03812913 X E. f
50
47
(1)
UW Orionis
JD Hel(Min.l)
-
301
2447172?2829 + 2:‘0381371 X E + 4.96 X IO-” X E’. 18
54
f
(21
1.10
In the calculation we found four points with O-C as much as 0.1-0.9 d, which seemed to be caused by outstanding errors. These were discarded in Whitney’s paper, and so we followed the practice. Photoelectric minimum times were given weight 2 and other tines, weight 1. From epoch formula (2) we have AP/P
= 4.87
x lo-lo
= 1.51 x lo+
s/yr,
showing that the period has a tendency to increase slowly. As may be seen from the O-C diagram in Fig. 2, most of the points come from visual and photographic observations and there is a large scatter, hence this tendency can only be regarded as a possibility at the present and should be confirmed with further photoelectric measurements. (0-C)”
;jj
- 10000
.-1400u
Fig. 2 O-C diagram of the minimum times of UW Ori. Only our 3 measurements (triangles) were photoelectric, the others (crosses) were all photographic or visual.,
TABLE 4a inc.
Normal Points
of the V Light
Curve
ior.
N
N
0.0143
0.1699
2
0.4716
0.2469
0.0212
0.1973
2
0.4787
0.2347
3
0.0269
0.2113
2
U.4834
0.2292
2
0.0341
0.2242
3
0.4997
0.1256
7
0.0439
0.2364
3
O.%lOO
0.2295
5
0.0677
0.1769
3
11.520~1
0.24116
2
0.0774
,I.:"~?5
z
11.554ll
u.27u5
2
0.0901
0.3IOll
4
0.S56.6
0.2665
1
0.1216
0.3425
7
0.5651
0.2965
3
0.1432
0.3106
7
0.5757
0.3072
3
0.1619
0.3603
7
0.5693
0.3224
6
0.1966
0.3660
I.7
0.6061
0.3365
5
0.2312
0.3736
R
0.6561
0.3620
7
0.2554
9.3764
9
0.675s
0.3660
2
0.2772
0.3729
II
0.6944
0.3722
7
0.3297
0.3632
II)
0.7315
0.3772
7
0.3701
0.3509
7
0.7677
0,371o
3
0.3600
0.3434
5
0.7972
0.3691
I6
6
302
ZHANG Rong-xian et al.
TABLE 4a (contd.) phase
int.
0.3905
0.3302
0.4050 0.4180
inr.
N
U.8422
0.3576
24
0.32111
0.8800
0.3434
9
0.3164
0.9013
0.3269
6
0.4272
0.3us7
0.91411
0.3100
6
0.4341
0.2945
0.9344
0.2Y13
33 9
PhW
0.4437
0.2799
0.9536
0.2464
0.4524
11.2t,9(1
U.9‘61
II.ZLJ"
9
0.4621
n.25Y2
".99,X
O.IRRI
6
TABLE 4b
Nomal Points of the B Light Curve
,111.
N
yhrre
,I,,.
N
0.0146
0.2912
2
0.4416
0.4453
6
0.0216
0.3102
2
0.4533
0.4272
7
0.0258
Il.3230
0.4684
0.3934
9
11."29(1
I,.,,,,,
,1.47'>,1
II.(76"
4
U.U.(611
11.,5117
I ? L
,1.49,,,
0. IDIJ
5
0.0443
0.3712
3
0.5065
U.3607
6
0.0640
0.4355
2
0.5201
0.31142
2
0.0719
0.4487
3
0.5572
0.4461
4
0.01117
0.4759
2
0.5601
0.4662
3
0.0926
0.4949
3
0.5791
0.4876
4
0.1310
n.54In
8
0.5966
0.5173
6
0.14118
Il.5517
5
lJ.61UY
0.5356
3
0.1641
0.5615
.4
0.6697
0.5703
9
0.1831
11.5711
?
0.7039
0.5820
6
0.2072
0.5835
R
0.7307
0.58311
0.2386
n.5Y93
16
0.7550
0.5876
0.2696
n.5Y71
8
0.7971
0.5778
18
0.2841
0.5055
6
0.Y420
0.5595
27
0.3on1
0.576'1
24
n.879Y
(I.5318
9
0.3296
0.5684
18
0.9011
0.5076
6
0.54')(
39
0.9146
Il.4819
6
U.5,,',
6
,,.',,-,.I
~I.4371
33
0.3126
u.53lJ7
1u
O.Y536
0.3863
9
0.3996
0.516,
6
0.9672
0.3442
9
0.4152
0.4942
9
0.9934
0.2912
6
0.4297
0.4729
7
:0.3618 0.36Yll
7 18
4. PHOTOMETRIC SOLUTION First, the observations were grouped into normal points according to the epoch formula (1). There were 52 normal points in the V curve (TABLE 4a) and 51 in the B curve (TABLE 4b). We used the well-known Wilson-Devinneymethod of light curve synthesis to solve for the orbit. The main part of the light curve used comes from the 1986.10-1987.1 season, part of the phase (0.0-0.1 and 0.5-0.6) uses the 1987.10-1988.1observations.The spectral type of the star is B, its subclass was not known. For
UK Orionis
303
this, we used our outside eclipse UBV measurements, applied extinction correction and, UWOri being located on the galactic plane, we corrected for reddening using Crawford’s method [El, then with reference to Popper’s results [El we found the spectral type to be Bl. This is further checked with the UBV measurements of the comparison star, for which the spectral type is known. Hence we adopted the spectral type of the main star (Component 1)‘ of IJUOri to be Bl, with an effective surface temperature of 25400°K. We assumed the thermal albedo and gravity darkening coefficients to be 1.0 for both components and the x U.Wl,limb darkening coefficient to be ‘7 0.25 in V and-O.30 in B. We began by assuming a detached model, but 0.015 we found Component 2 converging . towards the critical surface during the iteration, so we changed to a 0.014 semi-detached model. From the residual-mass ratio diagram (Pig. 3) we see that the residual ; is the least at q =0.513. The o:'L L." Q corresponding photometric solution is as given in TABLE 5. The results Fig. 3 show that Component 1 is the more massive component. The coefficients A, q and x were fixed rather than adjustable because the spectral type was probably uncertain by one subclass and different phase intervals were observed at rather different times.
I
+J
I .,. +-----
Y
TABLE 6
Photometric
COlOr
w(L,+L,)
”
--___
=*
of UU Ori B45UOA
0.668*0.001
0.686*0.001
0.25'
0.30.
f, _____-..~
Eolution
5suux
lJ.25*
._.
I
0.30. 86:39*0:14 0.r13~0.014
4=Wm, corn,'.I
--~_____9
1.U'
A
1.1).
Tn~
254UO'
0
comp.2 1.0* 1.U' 21169*60
3.U667f0.0071
2.9011**
r(PUle)
0.3864~0.0013
0.301S~0.0006
r(poinc)
0.4536~0.0022
0.4319-+0.0008
r(ride)
'l.4054~0.0016
u.31s1*0.0007
r(back)
0.4252~0.0021
Qt..
*assuraed
I **theoretical
0.3475*0.0007 2.9OII**
value
5. SBSULTS ANDDISCUSSION From
almost
the preliminary solution contact, semi-detached
we see that UK Ori is an early-type, binary where the main component is of
304
ZHANG Bong-xian
et al.
spectral type Bl and the secondary, B2. The secondary is the less massive one, it fills its critical surface while the main, more massive star nearly does so, with a degree of contact, r,/rl(Q,t,) q 0.93, very similar to TX Cas (101. Because there are no radial velocity measurements, we cannot derive the absolute parameters of the binary, but we can use the method described by ZHAI Di-sheng et al. 1111 and discuss the evolution of the system on the basis of the relative parameters given by the photometric solution. Recently, ZHAI Di-sheng et al. [12] used the absolute parameters of 171 components belonging to ‘88 two-spectrum detached binaries and re-calibrated the empirical ZAM8 (zero-age main sequence)
mass-radius relation. This had a gradient of a = 0.642 in the log R-1ogW diagram for spectral types between 09 and F6. If both components are ZAMS stars, then we should have log(Rz/Rl)/log(Mz/M,) = 0.642. The left side can be expressed in terms of the relative parameters as log(rz/rl)/logq, and this is equal to 0.38 from our solution. This is clearly less than the above value of 0.642. If we assume the more massive comnonent is on the ZAM8, then the less massive one has clearly evolved-out of it; if ml itself has already evolved to some extent, then ms will have evolved to an even greater extent. -1 This is consistent with our finding me filling its Roche lobe (see Fig. 4), that is, UW Ori belongs to the Algol type of semi-detached binary in which the me is the component that is losing mass. If -_.._the suggestion that the period is increasing turns out to be true, then it will be probable that ~712is Fig. 4 continuing losing matter to ml. If we assume ml to be still on the main sequence, then from the mass-spectrum relation we can find its mass to be about 13 &, hence we derive a radius of ~6.4 b, and for m2, ~6.7 & and -5.Ok. Then on the mass-radius diagram [12], m2 will still be within the main seqeunce band. Hence UW Ori is probably a product of Case A mass exchange. By means of Mochnacki’s formula parameters given by the present
[13], we can use the relative solution to calculate the mean
densities of the two components and we find the ratio &/& = 0.92, quite close to 1, so m2 indeed has not undergone much expansion and this is consistent exchange.
with the above deduction
of Case A mass
Thus, UW Ori is a new almost contact semi-detached binary. Analysing its features will undoubtedly contribute to the study of the evolution of binaries with non-constant mass exchange. Because the spectral type was not directly observed, we repeated the calculation assuming the spectral type of ml to be B5 or B9. We found that, as the assumed spectral type gets later, q increases (to nearly 1 at B9), but the configuration is not greatly changed,
UU Orionis
305
m2 still fills its Roche lobe while the degree of contact of ml changes slightly. For better determinations of the absolute parameters of the system, spectroscopic observations are very necessary.
REFERENCES [ll Lecher, W., AN 187 (1911), 191. 64 (1959), 258. [21 Whitney, S., A.J., r31 Ahnert, P., Mitteilungen uber veranderliche sterne, Berlin-Babelsbergund Sonnenberg No.643. [41 Zinner, S., Veroffentlichungender Remeis-Sternwarte,Bamberg. 1, 3. t51 Wood, F.B. et al., A finding list for observers of interacting binary stars, 1980. (61 Banachiewice, T., Rocenik astronomiceny obserwatorium Krakowskiego Nr. 58 (1987). (71 Kukarkin, B., Gen. Catalogue of Variable Stars, Moscow, 1970, 1986. 88 (1976), 917. (81 Crowford, D.L., PASP., ~. [91 Popper,D.M., Ann. Rev. Astton. Astrophys. 18(1980), 115. [lOI ZHAI Di-sheng, ZHANG Rong-xian, ZHANG Ji-tong and LI Qi-sheng, Chin.Astron.Astrophys.12/1(1988)60-69. =ActaAstron.Sin. 28/l (1987) 71-81. 1111 ZHAI Di-sheng, LEUNG K.C., ZHANG Rong-xian and ZHANG Ji-tong, Chin.Astron.Astrophys. 9/2 (1985) 139-144. = Acta 5/l (1985) 26-35. (12) Zhai, D.S. and ZhangX.Y., Publ. BAO., 12 (1989) 113) Mocnacki, S.W., Ap. J. 245 (1981), 650