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Infrared radiation oF RS CVn systems
Pergamon Journals. Printed in Great Britain 0275-1062/87$10.00+.00
Chin.Astron.Astrophys.II (1987) 328-336 Act.Astrophys.Sin.1 (lm?) 255-265
INFRARED
RADIATION
WANG Gang,
OF RS CVn SYSTEMS
HU Jing-yao,
QIAN
Zhong-yu,
ZHOU Xu
Beijing Observatory, Academia Siniea
Keywords Stars: RS CVn systems - infrared
Received 1986 July 15
ABSTRACT We give the results of our J, H, K photometry on 41 RS CVn systems and the data on 40 RS CVn systems identified with IRAS point sources. For those systems in which the components have individual spectral types, we discuss their infrared color excess. We found only very few systems showed infrared excesses. (UX Ari, Z Her and HR 1099 in the near infrared and SZ Psz at 12l.m). For systems having fluxes at 12 and 25~ and K magnitudes, we plotted a color-color diagram and found the majority of points to be lying close to the black body line. These observations are in conflict with Biermann and Hall's statement [1] that infrared excess is a general characteristic of RS CVn systems.
1.
INTRODUCTION
Hall 11975, [Z]) defined RS CVn type close binary systems as follows: orbital period between 1 and 14 days; the hotter component is an F or G main sequence star or subgiant; strong CaII H and K line emission outside eclipse. More and more observations since have confirmed Hall's spot model [3], namely in this type of close binary, the components have high rotational speeds due to tides, while the structure of the late-type star causes it to have a convection layer of sufficient depth for the energy accumulated through the dynamo mechanism to be released in the form of surface activities, as happens on the Sun, only on a much larger scale. RS CVn systems outside eclipse show approximately sinusoidal variations, called photometric or migrating waves. This phenomenon has been explained in terms of non-uniform surface brightness (due to the presence of spots) and change in period through modulation by rotation. However, in the early stage of the study, the hypothesis of non-uniform absorption by circumstellar matter was also proposed. This led to an interest in the infrared photometry of these objects. Because a few typical systems (e.g. HR 1099) showed abnormal emission in infrared, Biermann and Hall [l] thought that either or both components having infrared excess was a general characteristic
of RS CVn systems. At present, the spot model as the cause of outside eclipse light variation has generally been accepted. A number of infrared astronomers, e.g. Verma et al. 141, Berriman et al. [5] and Antonopoulon [6,7,8], accepting the premise that RS CVn systems have hfrared excess, have carried out observations in an attempt to find the cause of the infrared excess. However, the number of objects observed and the accuracy of the observations are not sufficient to establish that RS CVn systems in general possess infrared excess. For a better understanding of RS CVn systems, particularly their infrared characteristics, we used an In-Sb infrared photometer [lo] on the 60-cm reflector of Beijing Observatory and measured the J, H and K magnitudes of the 41 systems accessible to us in Hall's list [9] of 84 systems. Section 2 presents the observations, data treatment and the observed results. Section 3 presents results from the IRAS point source data: 40 of Hall's 84 systems having been identified as IRAS point sources. In Section 4 we discuss the near infrared characteristics of those systems in which snectml tynes . arc availahlc for the separate components: 13 out of ,the41 systems we observed and 10 out of the 40 systems identified as IRAS point sources. In Section 5, we present the two-color diagram of systems observed both by us and IRAS. 1
329
RS CVn Stars in Infrared
2.
NEAR INFRARED PHOlOMETRY OF KlRTY-ONE RS CVn SYSTEMS
Our observations were carried out on the 60 cm reflector of Xinglong Observing Station, Beijing Observatory, complemented with an oscillating secondary. The detector used was a nitrogen-cooled (77K) In-Sb instrument. A detailed description of the instrumentation has been given by QIAN, thong-yuet al. [IO]. We used the standard stars given by Glass [ll]. Atmospheric extinction and magnitude reduction coefficients were simultaneouslysolved according to the following equations: 1.- 111~ f @a/J + u&J - K) + 0,/X-t_ a,,X(J -K) 11, -
QIH+ ad
f& -
PIE + UxK + a,x(J -
f
@,H(J - H) + U,HX-Ia,,,X(J - H) K) + CZ,~X-t- G,~X(J -
K)
(1) t
in which X is the air mass. From 15 sets of observations on 14 standard stars made on 1984 March 16, we derived the following reduction formulae: 10- 23.33t- 1.0071 + 0.65(J - K) -0.31X - O.Z9(J - K)X & = 22.88 -I- l.OU+H+ 0.32(J - H) h’o -
0.10X -
O.l4(J -
H)X
(2)
22.40-Il.OOlK+ O.O9(J -K)0.16X- U.U3(J-K)X t The standard measuring errors were UJ=0.04, UH=0.03, OK=0.03. We used fairly long integration times, a 3. RS CVn SYSTEMS IDENTIFIED AS IRA.5SOURCES typical set was formed from 7 integrations of 10 seconds each. The mean scatter of the During 1983, the Infrared Astronomical individual integration about the set mean Satellite, JIRAS1 iointlv sent bv USA. UK and gives a measure of the instabilitiesof the the Netherlands completed a patrol of'nearly atmosphere, the instrument, and the signal 97% of the whole sky at four wavelengths, 12, within the 10 seconds interval of integration, 25, 60 and 80 Pm, during its ten months of and reflects to some extent, the measuring flight. The relevant data began to be accuracy. For the brighter stars, (J,H,K released in 1985, in the form of magnetic brighter than 4.0), signal may be 1001~or tape providing the data on quarter of a greater. For infrared magnitude 6-7 stars, million point sources 1111. Ihe completion this ratio falls to about 10. The correspof the IRAS patrol provided valuable material onding measuring accuraciesare between ~0.01 for the study of the infrared radiation of and r0.1 mag. A great part of our measureheavenly bodies. A search for the 84 RS CVn ments of the 41 systems had accuracies in systems on Hall's list amo-g the identified this range, which could be taken as our IRAS point sources (identifiedby SAO numbers) measuring accuracy. This range is consistent resulted in 40 being common to both lists. with the values of oJ, eH and oK, obtained This work was done on the VAX 11/780 computer elsewhere. of Beijing Observatory. The IRAS data for The observations were made in March, these 40 systems are reproduced in TABLE 2. June and October of 1984, and we measured the The first column gives Hall's serial number, outside eclipse J, H, K magnitudes of a total Columns 2 and 3 give the star name and the of 41 RS CVn systems (plus a number of last parts of the SAO and IRAS (1950.0) standard stars). TABLE 1 gives the observed coordinates. Columns 4, 5 and 6 give the flux results, after being corrected for atmospheric densities at 12, 25 and 60 nm, in units of extinction and reduced to the magnitudes. 3Y. The letter H following the numbers means Column 1 gives Hall's serial number; Column high quality, M means medium qulaity, and L means upper limit only. As very few sources 2, the epoch of observation in heliocentric &lian Days; Column 4, the orbital phase, or have precise values of the flux at 100 pm, the phase of the photometric wave in case these values were omitted altogether. of non-eclipsing systems; in the last column T stands for total eclipse, P for partial and N for non-eclipsing system. INF~R~D EXCESS IN RS CVn SYSTEMS 4. Of course, since the systems show light variations outside eclipse, what we got is If low-temperaturespot areas are present on not the mean magnitude outside eclipse, one or both components of a binary system.or if there is a cool, third body, or if there rather, it has the character of a random sample observation, (of course, for highly exists circumstellar matter which absorbs the visible radiation of the central stars, and eclipsing systems, measurements during eclipse were excluded). Fortunately, the re-radiates in the infrared, or if there is amplitude of the migrating waves in these emission from thermal plasma, or if there is heavy interstellar and circumstellar system in the infrared range is compatible absorption, then there will be more infrared with our measuring accuracy, [G].
HANG et
330
Table
1
Resulta of lnfrarcd
al.
Photometry
of
RS
CVn
Systems
-J. D. 445000+
NO. 2
2.82
2.22
2.13
2.38
2.24
2.14
.2778
0.47
2.87
2.23
2.13
0.66
2.29
1.53
1.37
0.66
2.24
1.51
1.40
0.66
2.29
1.55
I .34 3.76
I
.2793
5
6
)hO .3332
0.15
4.80
4.05
.336X
0.15
4.80
4.07
3.7B
.34u3
0.15
4.83
4.11
3.83
780.0965
Aur
dipsc
0.47
.?71
Ari
K
0.47
179.2646
JX
H
~
.2736
‘80.2686
!rta
J
phase ___
7.04
7.59
0.16
6.78
1.Rl
N
T
0.44
766.0417
0.41
4.40
4.66
3.46
.0500
0.41
4.38
4.6s
3.47
.0563
0.41
4.24
4.67
3.46
986.3451
0.91
4.16
3.55
3.48
II
986.3570
0.27
5.37
4.94
4.92
N
15
7n4.2319
I
10
17
II
21
24
25
Alpha
Aor
12 Call
1111 b283
13
‘1’Z
AS
Dra
HR
0.05
6.98
6.37
6 .I0
0.05
7.03
6.32
6.19
9R4.0(179
0.12
3.67
3.54
3.43
.n741
0.12
3.65
3.54
3.42
.0771
0.13
3.67
3.53
3.42
0.79
4.22
3.95
3.88
.2210
0.79
4.29
3.99
3.96
.2247
0.79
4.24
3.97
3.08
0.70
4.05
3.81
3.76
.3556
0.70
4.02
3.76
3.72
780.3472
CrU
7125
.3632
0.71
4.17
3.86
3.81
786 .I340
0.91
6.80
6.33
6.10
.1402
0.92
7.10
6 .?b
6.18
0.66
2 .Yb
2.09
1.86
.3035
0.66
2.88
2.09
1.88
.3104
0.66
2.88
2.07
1.85
0.06
2.47
2.03
1.92
0.06
2.62
2.10
1.86
0.26
6.38
5.79
5.59
.3600
0.2G
6.37
5.58
5.bb
.3637
0.26
6.21
5.84
5.65
2.67
1
.I729
2.56
1.86
.I806
2.62
1.9!
786.2972
9x0.0735 .0780 26
27
RZ
980.3559
Eri
Sigma
Gem
N
.2417
980.2174
Cct
1.24
-1.86
N
780.0354
-
-
1’
780.1639
.8Y
1.64 1.64
:
1
.bb
)u
N
N
N
N
N
T
N
331
RS CVn Stars in Infrared
TABLE
NO.
J. I). 4450UUf
2R
7n4.3434
34
36
37
40 41
43
45
54
55
3.14
3.76
4.38
3.92
3.86
.3563
0.23
4.25
3.92
3.92
ti61 .23X2
0.76
4.93
4.53
4.23
.?743
0.78
4.35
4.39
4.34
.2799
0.78
4.91
4.42
4.38
0.25
4.94
4.40
4.24
.?I34
0.25
4.93
4.41
4.28
86 I .2986
0.73
5.30
4.53
4.35
.3021
0.73
5.27
4.51
4.32
.3063
0.73
5.29
4.51
4.33
0.56
5.34
4.44
4.22
.1865
0.56
5.22
4.43
4.22
.I910
0.56
5.18
4.41
4.24
0.20
4.61
3.89
3.71
.2450
0.20
4.64
3.86
3.61
.2493
0.20
4.62
3.$7
3.68
979.2401
T
N
N
0.20
3.35
2.86
2.77
.2444
0.20
3.31
2.82
2.75
.2528
0.20
3.43
2.x9
2.81
0.31
7.11
6.12
6.40
T
0.71
5.93
5.01
4.72
N
0.71
5.82
4.94
4.73
780.2368
786.0076 980.1727
0.95
6.94
6.31
6.18
.3214
0.95
7.07
6.41
6.20
.3243
0.95
7.02
6.34
6.17
986 .I970
0.36
6 .OJ
5.29
4.91
.2001
0.36
G .Ol
5.29
4.94
.2033
0.36
6.03
5.30
4.99
0.77
3.21
2.53
2.19
0.77
3.19
2.54
2.25
986.3182
986.2137
0.73
4.21
3.51
3.21
.2373
0.73
4.21
3.49
3.20
.2409
0.73
4.21
3.48
3.20
0.17
6.06
5.82
5.04
.0527
0.17
6.14
5.d4
5.81
.0565
0.18
6.09
5.85
5.86
0.32
4.53
3.78
3.58
0.32
4.56
3.83
3.6
986.2327
980.0418
786.1639 .I701 .1764
56
P
4.35
.2168 47
eclipse
0.23
.1760 42
K
0.23
979.1817
(contd.)
H
.35uo
979.2083
35
J
1
790.2889 .2965
0.32
4.56
3.83
3.63
0.22
4.26
4.25
4.28
0.22
4.29
4.28
4.30
N
T
P
N
N
P
N
I N
WANG
332
et al.
TABLE No.
st3r
name
J. D.
2445000+ .3049
57
HR
58
HR 7275
6469
HR
7428
HD Sb590
71
BD+611211 I-ID160538
74
1ID 175742 lID 178540
N
3.25
N
0.91 0.91 0.91
4.63
3.80 3.80 3.79
3.56
4.61 4.67 4.07 4.06
3.33 3.33
3.20
0.35 0.35 0.36
6.33 6.32
5.73 5.73 5.79
0.35 0.35
7.77 7.73
7.05 7.04
5.07 5.07 5.05
4.34 4.37 4.33
979.9995 9tio.0039
6.20
5.73 5.75
5.60
6.17
9110.02x5
6.13 6.09 6.2X
5.81 5.82 5.86
5.75
5.96 5.94 5.93
5.56 5.52 5.51
5.28
786.2618
980.1226
785.1764
785.1139 .I257 786.3361
.0367 HD
26337
4.27 3.64
.0326
76
4.20
3.51 3.51 3.51
.3424 .3479 73
4.21
eclipse
3.70
-1026 .I861 68
K
4.31 4.29 4.25
.I284 63
H
4.07
.2743
HD 216489
J
0.66 0.66 0.66
786.2201
.2681
60
0.23
780.3979 .2271 .2333
59
phase
1 (contd.)
986.2896 .2928 .2980
6.29
3.26 3.28
N
3.58 3.54
N
3.18 5.55
N
5.60 5.63 6.81
N
6.83 4.10
N
4.14 4.09
N
5.67
N
5.70 5.71
N
5.27 5.27
77
HD 37847
785.0125
6.27
6.60
6.84
N
78
HD 136905
784.2847 .2917 .2978
3.99
3.21 3.13 3.14
2.94
N
radiation than a normal body of the same spectral type has, that is, there will be infrared excess. Accordingly, for those systems in which both components have known spectral types, we calculated their flux densities in the near infrared region or the 12 urnregion under normal conditions. These calculated values will be used in a comparison with their observed values. Of the 41 systems we observed in the infrared, 13 have components with separately known spectral types. Using the data of visible luminosities given in "Astrophysical Quantities" [12], and the infrared colors given by Koornneel [13], we calculated the colors (V-J)c, (V-H), and (V-K)c, that normal stars of the given spectral types would have.
3.95
4.01
2.92 2.88
From our observed J, H, K values, and the V values given by Hall, we derived the observed colors (V-J),, (V-H), and (V-K),. Their differences are the infrared excesses given in TABLE 3. Of course, the values given in TABLE 3 include errors in magnitude measurements, in spectral type etc. Nevertheless, the general feature shown by the histogram of these values is evident (Fig. 1): although there is a slight tendency towards positive values of the excess, we cannot say that infrared excess is a general property of RS CVn systems. Of course, one could affirm that, for some systems such as UX Ari, HR 1099 and 2 Her, there is definitely an infrared excess. (For UX Ari and HR 1099, the infrared
RS CVn Stars
‘T.ble 2 Starnarxrc
Nu. 2 3 4
And
41.0
9’44 9’44
Lamixla
06.5
1’14
233SO-t.4610
05.6
0’48
UX Ari
33.0
2’32
32.7
2’28
03235-k 2832 6
Alpha
Atlr
302.8
6’46
50.6
7’15
05018+ 5857
50.1
7’15
If
54 Cam
32.1
4’51
07585+5724
32.0
4’51
17
HR 8283
49.8
6’17
21388-1416
49.7
6’25
18
I3 CCf
40.4
2’04
uo327-0351
43.11 1’50
21
‘G
c;rl#
4x.3
9’03
16127-+-3359
47.3
9’00
25
IIR 7125
27.x
9’36
18504i-5919
2a.4
9’37
27
Siprt;r Cktrr
11.4
WI3
07401 f 2900
10.9
11’19
Al
Lac
39.5
9’45
22U66~452~
3x.0
9’3d
IiR
57.4
9’27
22029i-4659
57.x
9’27
HR 8575
02.x
6’00
34 35 36
Lat
222wo+4905
02.7
5’S&
37
93 Leo
24.5
9’49
II453+2029
24.0
9’Sl
41
II Peg
29.1.
1’18
23525+2821
30.6
1’16
43
sz
50.6
4’10
23~~8~~224
51.5
4’16
#S
33 Pu:
46.5
9’14
ooo27-0559
45.9
9’15
46
‘IT Pyx
34.0
7’11
?$C
08575-2737
34.4
7’23
47
HR 1099
13.2
5’33
03342~0025
12.5
5’24
48
TZ ‘I%
27.1
4’11
02094-I-3009
27.4
4’05
$1
118 4374
31.2
Ii’39
Ifl54+3148
29.8
8’20
Kpsilon UMi
00.9
7’22
53
I .293H+-OIII
2,9338+OOH
1.373B401H
3.274Fe+OOH
6.459X-OIW
4&?36E-OIM
4.007E-OIL
ZS9 *5 6’53
I2 Cam
05130f4556 10
lb A. 1kc.
39.8
And
Infrared
KS CVD Systems identified w IRAS SDUIC~S
ao446+2359
‘ha
in
2.361E+02H
4.69SE-OIH
5.693E+OlW 5.805&-OIH
4.019&-OfL
2*482E-
4.025E-Olt
OIL
I .669E-I-OOH
3.992E-OIL
t .23Sf:+OQW
4.913%.OIL
3 .S%E-
I .461E+QxJH
3.783E--0Il-I
4.033Ec-OiL
OIL
3.9?7E-OIM S,OJ5E--OIM
9*9GIE-OIW
S.O41E--01s
2.4?5&-OIL
4.0231’-
2*598E-OlH
4.024E-OLL
4*066E-OIW
3+579E-OIL
S.ZGbE--0iH
4.066E-OIL
3.39%-
3.575E--01L
2.6otE
OlL GlL
4.066E-
0%
Ott
4,00@E-OIL 3.938&-OIH
2,4836-OIL 6.3SSE-011%
3.52ZE+OOl-i
9.1&W--0lH
4,018E.-OIL
1 l343E+oOH
4.016E-OIL
334
WANG et
al.
TABLE
16510+9207
00.9
7’21
5G
HR
33.9
6’17
13325+3726
34.3
6,1X
57
HR 6469
05.0
1’21
17200+4001
05.2
1’17
58
HR
IS.5
0’43
19072+5220
15.5
0’42
59
HR
10.1
7’30
19301+5537
11.0
7’34
60
1411 216489
07.6
0’31
5110
7275
7428
22521+1640
ox.0
0’31
61
CF Tut
26.7
5’23
00515-7455
30.2
5’10
bS
HI)
18.2
3 40
17121-6653
11.0
3’38
70
39 Get
03.8
5’47
01140-0245
04.0
5’47
71
HI>
03.3
5’33
17340+7415
03.x
5’34
76
HD
15.2
1’27
155555
16053X
26337
04072-
0801
17.1
1’26
30.5
9’24
31 .6
9’25
46.3
5’54
47.1
6’01
5x.4
0’45
19369-0610
S7.6
0’52
HD
09.5
0’55
77
Ill)
7R
HD
79
III)
80
82
HD
83
84
37x47
05385-
2019
136905
15207-
0626
lY5SlO
190540
20031-
1850
09.0
O’S6
41.0
6’18
19346+2746
39.7
6’09
HD
19.7
9’19
01203+0709
20.6
9’30
HD
06.8
1’35
05.7
1’38
185151
8357
155638
17090+4901
2
(contd.)
6.245E+OOH
1.5S6E+OOH
5.4SSE-OIM
1.766E+OOH
5.45lE-OlH
4.026F.-IJIL
1.331E+OOH
3.539E-OIH
4.034E-OIL
2.330E+OOH
5.471E-01H
4.032E-OIL
1.918E+OOH
5.14bE-OlH
9.81oE-olH
2-.763E+OlH
7.179E+OOH
1.180E-kOOM
4.012E-011-1
2.47bE-OIL
4.030E-OIL
6.98@E-OlH
3.130E--0lL
4.0?3E-OIL
2.393E+OOH
6.525E-OIH
3.559E-OIL
1 .1631<+00H
3.01113-OlH
4.032t-
3.?45e--0111
IJli
4.ozot-011.
G .5lbl~-o1H
2.+B?E--OlL
4.026t-OIL
5.683E-OlH
3.717E-OlL
4.004E-OlL
,4.859E-0111
2.878F.-OlL
4.484E-OlL
3.455X-OIH
8.36lE-OIL
7.307E--01L
7.93lE-OIH
?.479E-OIL
6.310E-OIL
6.617E-OlH
3.569E-OIL
3.555E-OIL
2.974E-OlH
2.472E-OIL
4.098K-OIL
RS CVn Stars
I
rtar name
I E(V-J)
335
Infrared
Near Infrared Excess of RS CVn Syatcms
Table 3
NO.
in
I E(V-H)
I E(V-K)
NO.
star IIMC
E(V-J)
E(V--HI
W--K)
--
4
UX Ari
6
alpha Aur
-0.25
0.37
-0.14
0.74
15
RS cvn
-0.29
-0.02
24
AS Dra
-0.01
28.
2 Her
34
AR Lac
-0.04
40
AR Man
-0.93
1.74
0.93
42
LX Per
-0.14
0.11
0.13
43
sz Psc
-0.23
0 .oa
0.32
0.15
47
HR 1099
0.23
0.58
0.76
0.13
0.28
54
ER Vul
0.16
0.12
1 .92
1.93
55
HR 4665
-0.62
-0.66
-0.59
0.21
56
HR 5110
-0.19
-0.45
-0.60
-0.20
0.16 -0.5R
-1.07
excess was also confirmed by Verma’s But we must also point out observation [4]). that, for some systems such as AR Mon, HR 4665 and HR 5110, there is, in fact, an infrared “deficit”. This deficit, if verified by further observations would mean the presence of some “hot” regions, or the existence of some nonthermal source in the visible region.
Nr-----l
0.02
I theoretical values of the flux density at 12 urn were calculated from Kurucz’s model atmosphere [14] and the IRAS observed values were corrected for color [ll]. The results are shown in TABLE 4, and the histogram of E(V-[12]) is shown in Fig. 2. Again, a slight tendency towards positive values is shown; but apart from SZ Psc, the values differ little from measuring errors, hence, again, we cannot say that infrared excess is a general feature of RS CVn systems.
4
!lildbd 2
- 1.4,
0.2
-0.6
I.o
01
1.8
E (V-K)
Fig.
1
Histogram
of
Fig.
amongst the 40 RS CVn systems Similarly, that have been identified as IRAS sources, there are 10 with individual spectral Using classifications of the components. the same method, we discuss the colors (V-[12]), [12] representing the flux density at 12 Pm expressed in magnitudes. The
NO.
I
Star
Name
I
0.4
0 E (V-(12))
E(V-K)
Table
-0.4
4
SP.
Infrared Excw
I E(V-12)
2
Historgram
E(V-[12])
There is, statistically speaking, a slight excess in the (K-[12]) color. A possible explanation is interstellar reddening. As we did not correct for interstellar extinction, a small, statistical excess could well have been caused by interstellar reddening.
of RS CVn Syttcma_at 12pm II NO.
I Star
Name
SP.
I
-0.03
46
TY Py;
GS+GS
-0.01
47
HR 1099
GRV+KlIV
-0.01
of
0.02 -0.03
48
TZ Tri
GSIII+G5III
0.14
0.20
53
Eps UMi
DAB-
0.18
0.42
65
HD 155555
GSIV+KOV-IV
PO+G5III
0.28
WANG
336
5.
et al.
TWO-COLOR DIAGRAM
Discussion of the question of infrared excess is made difficult by the limited number of RS CVn systems with components having individual spectral types. To exploit the available data, we construct a two-color diagram using the flux densities at 25um, 12 urn,and 2.2pm, the last derived from the K magnitudes. For 21 RS CVn systems having the relevant data, we plot log(fzs/f12) against log(f12/f2_2) in Fig. 3. The solid line represents black body radiation. We note I
I
I
I
-0.6
-0.6
that all the observed points lie close to the black body line, in the region occupied by normal stars. Only 5 And and HR 5110 are somewhat peculiar. For 5 And, Johnson's measured K value is 1.52, [15], and if we use this value, the point (representedby an unfilled circle) will also fall in the region of normal star. For HR 5110, Verma [4] gave K= 3.53, and this would again be located in the normal region. Why, for those two stars, do our measurements differ from others by more than the measuring errors? Whether it is due to real changes in the infrared magnitudes, or some other cause must await further observation for elucidation. (Our measurement of 5 And was made at a phase of 0.47 and the possibility of effect of eclipse should not be excluded out of hand). Nevertheless, generally speaking, the RS CVn systems fall in the region of normal stars of the two-color diagram and we again have no reason to believe that infrared excess is a general characteristic of these systems.
z > - 1.0 < ,M
6.
We have discussed the near and middle infrared emission characteristics of RS CVn type close binaries. 3 out of 13, i.e. 23% show a color excess in the near infrared region. In the 12 urnregion, only 1 out of 12, or 10% does. so. Their positions on the infrared colorcolor diagram are all in the region of normal stars, showning that there is no circumstellar dust. Our conclusion therefore does not agree with Hall's statement that infrared excess is a general characteristic of RS CVn systems.
-1.2
- I.1
Fig. 3
CONCLUSION
Two-color diagram of 21 RS CVn systems
REFERENCES
[ll
Biermann, P. and Hall, D., IAU Symp., 73 (1975), 381 (1975), part I, 287. [31 HU Jing-yao, Pubz.Beijing Obs.S'uppl.5 (1983), 17.
[21 Hall, D., IAU Colloq., 29
r41
Vtrma.
[51
Bcrriman,
R.
161
Antonopoulou,
P. G.
et
al.,
hrophy~.
Sprrcc
et
al.,
Mon.
K.
E..
Not.
Arrrophyr.
Space
SC;.,
A~zron. SC;.,
97(1983), Sot.,
161.
205(1963),
67( 1960),
859.
469.
171
Antonopoulou,
E.,
Anron.
Arrrophyr.
Sup&
52(1963a),
38,.
I61
An~~~opoulou,
E.,
Arrron.
Arrrophys.
St&..
53~ 19831,),
347.
1963. 161 Ilrll, D., Private Communication, [91 Hall, D., Private Communication 1983. PO1 QIAN, ihong-yuet al. Act.Astrophys.Sin.5 (1985), 230. Glass, I.S., Mon.Not.R.Astron.Soc. 171 (1975), 19. R. I... .~l,rruph)r. J., Suppl. Ser.. 40, I. ;:t; k;lirucr, K~urrnnceI, Jul~nwn,
Ailron.
J., I.
H.
ct
al..
Artrophyr.. Comm.
Lun.
128( 1963), Planetary
90. Lab.,
4(1966),
99.
Chin.Astron.Astrophys.II (1987) 328-336 Act.Astrophys.Sin.1 (lm?) 255-265
INFRARED
RADIATION
WANG Gang,
OF RS CVn SYSTEMS
HU Jing-yao,
QIAN
Zhong-yu,
ZHOU Xu
Beijing Observatory, Academia Siniea
Keywords Stars: RS CVn systems - infrared
Received 1986 July 15
ABSTRACT We give the results of our J, H, K photometry on 41 RS CVn systems and the data on 40 RS CVn systems identified with IRAS point sources. For those systems in which the components have individual spectral types, we discuss their infrared color excess. We found only very few systems showed infrared excesses. (UX Ari, Z Her and HR 1099 in the near infrared and SZ Psz at 12l.m). For systems having fluxes at 12 and 25~ and K magnitudes, we plotted a color-color diagram and found the majority of points to be lying close to the black body line. These observations are in conflict with Biermann and Hall's statement [1] that infrared excess is a general characteristic of RS CVn systems.
1.
INTRODUCTION
Hall 11975, [Z]) defined RS CVn type close binary systems as follows: orbital period between 1 and 14 days; the hotter component is an F or G main sequence star or subgiant; strong CaII H and K line emission outside eclipse. More and more observations since have confirmed Hall's spot model [3], namely in this type of close binary, the components have high rotational speeds due to tides, while the structure of the late-type star causes it to have a convection layer of sufficient depth for the energy accumulated through the dynamo mechanism to be released in the form of surface activities, as happens on the Sun, only on a much larger scale. RS CVn systems outside eclipse show approximately sinusoidal variations, called photometric or migrating waves. This phenomenon has been explained in terms of non-uniform surface brightness (due to the presence of spots) and change in period through modulation by rotation. However, in the early stage of the study, the hypothesis of non-uniform absorption by circumstellar matter was also proposed. This led to an interest in the infrared photometry of these objects. Because a few typical systems (e.g. HR 1099) showed abnormal emission in infrared, Biermann and Hall [l] thought that either or both components having infrared excess was a general characteristic
of RS CVn systems. At present, the spot model as the cause of outside eclipse light variation has generally been accepted. A number of infrared astronomers, e.g. Verma et al. 141, Berriman et al. [5] and Antonopoulon [6,7,8], accepting the premise that RS CVn systems have hfrared excess, have carried out observations in an attempt to find the cause of the infrared excess. However, the number of objects observed and the accuracy of the observations are not sufficient to establish that RS CVn systems in general possess infrared excess. For a better understanding of RS CVn systems, particularly their infrared characteristics, we used an In-Sb infrared photometer [lo] on the 60-cm reflector of Beijing Observatory and measured the J, H and K magnitudes of the 41 systems accessible to us in Hall's list [9] of 84 systems. Section 2 presents the observations, data treatment and the observed results. Section 3 presents results from the IRAS point source data: 40 of Hall's 84 systems having been identified as IRAS point sources. In Section 4 we discuss the near infrared characteristics of those systems in which snectml tynes . arc availahlc for the separate components: 13 out of ,the41 systems we observed and 10 out of the 40 systems identified as IRAS point sources. In Section 5, we present the two-color diagram of systems observed both by us and IRAS. 1
329
RS CVn Stars in Infrared
2.
NEAR INFRARED PHOlOMETRY OF KlRTY-ONE RS CVn SYSTEMS
Our observations were carried out on the 60 cm reflector of Xinglong Observing Station, Beijing Observatory, complemented with an oscillating secondary. The detector used was a nitrogen-cooled (77K) In-Sb instrument. A detailed description of the instrumentation has been given by QIAN, thong-yuet al. [IO]. We used the standard stars given by Glass [ll]. Atmospheric extinction and magnitude reduction coefficients were simultaneouslysolved according to the following equations: 1.- 111~ f @a/J + u&J - K) + 0,/X-t_ a,,X(J -K) 11, -
QIH+ ad
f& -
PIE + UxK + a,x(J -
f
@,H(J - H) + U,HX-Ia,,,X(J - H) K) + CZ,~X-t- G,~X(J -
K)
(1) t
in which X is the air mass. From 15 sets of observations on 14 standard stars made on 1984 March 16, we derived the following reduction formulae: 10- 23.33t- 1.0071 + 0.65(J - K) -0.31X - O.Z9(J - K)X & = 22.88 -I- l.OU+H+ 0.32(J - H) h’o -
0.10X -
O.l4(J -
H)X
(2)
22.40-Il.OOlK+ O.O9(J -K)0.16X- U.U3(J-K)X t The standard measuring errors were UJ=0.04, UH=0.03, OK=0.03. We used fairly long integration times, a 3. RS CVn SYSTEMS IDENTIFIED AS IRA.5SOURCES typical set was formed from 7 integrations of 10 seconds each. The mean scatter of the During 1983, the Infrared Astronomical individual integration about the set mean Satellite, JIRAS1 iointlv sent bv USA. UK and gives a measure of the instabilitiesof the the Netherlands completed a patrol of'nearly atmosphere, the instrument, and the signal 97% of the whole sky at four wavelengths, 12, within the 10 seconds interval of integration, 25, 60 and 80 Pm, during its ten months of and reflects to some extent, the measuring flight. The relevant data began to be accuracy. For the brighter stars, (J,H,K released in 1985, in the form of magnetic brighter than 4.0), signal may be 1001~or tape providing the data on quarter of a greater. For infrared magnitude 6-7 stars, million point sources 1111. Ihe completion this ratio falls to about 10. The correspof the IRAS patrol provided valuable material onding measuring accuraciesare between ~0.01 for the study of the infrared radiation of and r0.1 mag. A great part of our measureheavenly bodies. A search for the 84 RS CVn ments of the 41 systems had accuracies in systems on Hall's list amo-g the identified this range, which could be taken as our IRAS point sources (identifiedby SAO numbers) measuring accuracy. This range is consistent resulted in 40 being common to both lists. with the values of oJ, eH and oK, obtained This work was done on the VAX 11/780 computer elsewhere. of Beijing Observatory. The IRAS data for The observations were made in March, these 40 systems are reproduced in TABLE 2. June and October of 1984, and we measured the The first column gives Hall's serial number, outside eclipse J, H, K magnitudes of a total Columns 2 and 3 give the star name and the of 41 RS CVn systems (plus a number of last parts of the SAO and IRAS (1950.0) standard stars). TABLE 1 gives the observed coordinates. Columns 4, 5 and 6 give the flux results, after being corrected for atmospheric densities at 12, 25 and 60 nm, in units of extinction and reduced to the magnitudes. 3Y. The letter H following the numbers means Column 1 gives Hall's serial number; Column high quality, M means medium qulaity, and L means upper limit only. As very few sources 2, the epoch of observation in heliocentric &lian Days; Column 4, the orbital phase, or have precise values of the flux at 100 pm, the phase of the photometric wave in case these values were omitted altogether. of non-eclipsing systems; in the last column T stands for total eclipse, P for partial and N for non-eclipsing system. INF~R~D EXCESS IN RS CVn SYSTEMS 4. Of course, since the systems show light variations outside eclipse, what we got is If low-temperaturespot areas are present on not the mean magnitude outside eclipse, one or both components of a binary system.or if there is a cool, third body, or if there rather, it has the character of a random sample observation, (of course, for highly exists circumstellar matter which absorbs the visible radiation of the central stars, and eclipsing systems, measurements during eclipse were excluded). Fortunately, the re-radiates in the infrared, or if there is amplitude of the migrating waves in these emission from thermal plasma, or if there is heavy interstellar and circumstellar system in the infrared range is compatible absorption, then there will be more infrared with our measuring accuracy, [G].
HANG et
330
Table
1
Resulta of lnfrarcd
al.
Photometry
of
RS
CVn
Systems
-J. D. 445000+
NO. 2
2.82
2.22
2.13
2.38
2.24
2.14
.2778
0.47
2.87
2.23
2.13
0.66
2.29
1.53
1.37
0.66
2.24
1.51
1.40
0.66
2.29
1.55
I .34 3.76
I
.2793
5
6
)hO .3332
0.15
4.80
4.05
.336X
0.15
4.80
4.07
3.7B
.34u3
0.15
4.83
4.11
3.83
780.0965
Aur
dipsc
0.47
.?71
Ari
K
0.47
179.2646
JX
H
~
.2736
‘80.2686
!rta
J
phase ___
7.04
7.59
0.16
6.78
1.Rl
N
T
0.44
766.0417
0.41
4.40
4.66
3.46
.0500
0.41
4.38
4.6s
3.47
.0563
0.41
4.24
4.67
3.46
986.3451
0.91
4.16
3.55
3.48
II
986.3570
0.27
5.37
4.94
4.92
N
15
7n4.2319
I
10
17
II
21
24
25
Alpha
Aor
12 Call
1111 b283
13
‘1’Z
AS
Dra
HR
0.05
6.98
6.37
6 .I0
0.05
7.03
6.32
6.19
9R4.0(179
0.12
3.67
3.54
3.43
.n741
0.12
3.65
3.54
3.42
.0771
0.13
3.67
3.53
3.42
0.79
4.22
3.95
3.88
.2210
0.79
4.29
3.99
3.96
.2247
0.79
4.24
3.97
3.08
0.70
4.05
3.81
3.76
.3556
0.70
4.02
3.76
3.72
780.3472
CrU
7125
.3632
0.71
4.17
3.86
3.81
786 .I340
0.91
6.80
6.33
6.10
.1402
0.92
7.10
6 .?b
6.18
0.66
2 .Yb
2.09
1.86
.3035
0.66
2.88
2.09
1.88
.3104
0.66
2.88
2.07
1.85
0.06
2.47
2.03
1.92
0.06
2.62
2.10
1.86
0.26
6.38
5.79
5.59
.3600
0.2G
6.37
5.58
5.bb
.3637
0.26
6.21
5.84
5.65
2.67
1
.I729
2.56
1.86
.I806
2.62
1.9!
786.2972
9x0.0735 .0780 26
27
RZ
980.3559
Eri
Sigma
Gem
N
.2417
980.2174
Cct
1.24
-1.86
N
780.0354
-
-
1’
780.1639
.8Y
1.64 1.64
:
1
.bb
)u
N
N
N
N
N
T
N
331
RS CVn Stars in Infrared
TABLE
NO.
J. I). 4450UUf
2R
7n4.3434
34
36
37
40 41
43
45
54
55
3.14
3.76
4.38
3.92
3.86
.3563
0.23
4.25
3.92
3.92
ti61 .23X2
0.76
4.93
4.53
4.23
.?743
0.78
4.35
4.39
4.34
.2799
0.78
4.91
4.42
4.38
0.25
4.94
4.40
4.24
.?I34
0.25
4.93
4.41
4.28
86 I .2986
0.73
5.30
4.53
4.35
.3021
0.73
5.27
4.51
4.32
.3063
0.73
5.29
4.51
4.33
0.56
5.34
4.44
4.22
.1865
0.56
5.22
4.43
4.22
.I910
0.56
5.18
4.41
4.24
0.20
4.61
3.89
3.71
.2450
0.20
4.64
3.86
3.61
.2493
0.20
4.62
3.$7
3.68
979.2401
T
N
N
0.20
3.35
2.86
2.77
.2444
0.20
3.31
2.82
2.75
.2528
0.20
3.43
2.x9
2.81
0.31
7.11
6.12
6.40
T
0.71
5.93
5.01
4.72
N
0.71
5.82
4.94
4.73
780.2368
786.0076 980.1727
0.95
6.94
6.31
6.18
.3214
0.95
7.07
6.41
6.20
.3243
0.95
7.02
6.34
6.17
986 .I970
0.36
6 .OJ
5.29
4.91
.2001
0.36
G .Ol
5.29
4.94
.2033
0.36
6.03
5.30
4.99
0.77
3.21
2.53
2.19
0.77
3.19
2.54
2.25
986.3182
986.2137
0.73
4.21
3.51
3.21
.2373
0.73
4.21
3.49
3.20
.2409
0.73
4.21
3.48
3.20
0.17
6.06
5.82
5.04
.0527
0.17
6.14
5.d4
5.81
.0565
0.18
6.09
5.85
5.86
0.32
4.53
3.78
3.58
0.32
4.56
3.83
3.6
986.2327
980.0418
786.1639 .I701 .1764
56
P
4.35
.2168 47
eclipse
0.23
.1760 42
K
0.23
979.1817
(contd.)
H
.35uo
979.2083
35
J
1
790.2889 .2965
0.32
4.56
3.83
3.63
0.22
4.26
4.25
4.28
0.22
4.29
4.28
4.30
N
T
P
N
N
P
N
I N
WANG
332
et al.
TABLE No.
st3r
name
J. D.
2445000+ .3049
57
HR
58
HR 7275
6469
HR
7428
HD Sb590
71
BD+611211 I-ID160538
74
1ID 175742 lID 178540
N
3.25
N
0.91 0.91 0.91
4.63
3.80 3.80 3.79
3.56
4.61 4.67 4.07 4.06
3.33 3.33
3.20
0.35 0.35 0.36
6.33 6.32
5.73 5.73 5.79
0.35 0.35
7.77 7.73
7.05 7.04
5.07 5.07 5.05
4.34 4.37 4.33
979.9995 9tio.0039
6.20
5.73 5.75
5.60
6.17
9110.02x5
6.13 6.09 6.2X
5.81 5.82 5.86
5.75
5.96 5.94 5.93
5.56 5.52 5.51
5.28
786.2618
980.1226
785.1764
785.1139 .I257 786.3361
.0367 HD
26337
4.27 3.64
.0326
76
4.20
3.51 3.51 3.51
.3424 .3479 73
4.21
eclipse
3.70
-1026 .I861 68
K
4.31 4.29 4.25
.I284 63
H
4.07
.2743
HD 216489
J
0.66 0.66 0.66
786.2201
.2681
60
0.23
780.3979 .2271 .2333
59
phase
1 (contd.)
986.2896 .2928 .2980
6.29
3.26 3.28
N
3.58 3.54
N
3.18 5.55
N
5.60 5.63 6.81
N
6.83 4.10
N
4.14 4.09
N
5.67
N
5.70 5.71
N
5.27 5.27
77
HD 37847
785.0125
6.27
6.60
6.84
N
78
HD 136905
784.2847 .2917 .2978
3.99
3.21 3.13 3.14
2.94
N
radiation than a normal body of the same spectral type has, that is, there will be infrared excess. Accordingly, for those systems in which both components have known spectral types, we calculated their flux densities in the near infrared region or the 12 urnregion under normal conditions. These calculated values will be used in a comparison with their observed values. Of the 41 systems we observed in the infrared, 13 have components with separately known spectral types. Using the data of visible luminosities given in "Astrophysical Quantities" [12], and the infrared colors given by Koornneel [13], we calculated the colors (V-J)c, (V-H), and (V-K)c, that normal stars of the given spectral types would have.
3.95
4.01
2.92 2.88
From our observed J, H, K values, and the V values given by Hall, we derived the observed colors (V-J),, (V-H), and (V-K),. Their differences are the infrared excesses given in TABLE 3. Of course, the values given in TABLE 3 include errors in magnitude measurements, in spectral type etc. Nevertheless, the general feature shown by the histogram of these values is evident (Fig. 1): although there is a slight tendency towards positive values of the excess, we cannot say that infrared excess is a general property of RS CVn systems. Of course, one could affirm that, for some systems such as UX Ari, HR 1099 and 2 Her, there is definitely an infrared excess. (For UX Ari and HR 1099, the infrared
RS CVn Stars
‘T.ble 2 Starnarxrc
Nu. 2 3 4
And
41.0
9’44 9’44
Lamixla
06.5
1’14
233SO-t.4610
05.6
0’48
UX Ari
33.0
2’32
32.7
2’28
03235-k 2832 6
Alpha
Atlr
302.8
6’46
50.6
7’15
05018+ 5857
50.1
7’15
If
54 Cam
32.1
4’51
07585+5724
32.0
4’51
17
HR 8283
49.8
6’17
21388-1416
49.7
6’25
18
I3 CCf
40.4
2’04
uo327-0351
43.11 1’50
21
‘G
c;rl#
4x.3
9’03
16127-+-3359
47.3
9’00
25
IIR 7125
27.x
9’36
18504i-5919
2a.4
9’37
27
Siprt;r Cktrr
11.4
WI3
07401 f 2900
10.9
11’19
Al
Lac
39.5
9’45
22U66~452~
3x.0
9’3d
IiR
57.4
9’27
22029i-4659
57.x
9’27
HR 8575
02.x
6’00
34 35 36
Lat
222wo+4905
02.7
5’S&
37
93 Leo
24.5
9’49
II453+2029
24.0
9’Sl
41
II Peg
29.1.
1’18
23525+2821
30.6
1’16
43
sz
50.6
4’10
23~~8~~224
51.5
4’16
#S
33 Pu:
46.5
9’14
ooo27-0559
45.9
9’15
46
‘IT Pyx
34.0
7’11
?$C
08575-2737
34.4
7’23
47
HR 1099
13.2
5’33
03342~0025
12.5
5’24
48
TZ ‘I%
27.1
4’11
02094-I-3009
27.4
4’05
$1
118 4374
31.2
Ii’39
Ifl54+3148
29.8
8’20
Kpsilon UMi
00.9
7’22
53
I .293H+-OIII
2,9338+OOH
1.373B401H
3.274Fe+OOH
6.459X-OIW
4&?36E-OIM
4.007E-OIL
ZS9 *5 6’53
I2 Cam
05130f4556 10
lb A. 1kc.
39.8
And
Infrared
KS CVD Systems identified w IRAS SDUIC~S
ao446+2359
‘ha
in
2.361E+02H
4.69SE-OIH
5.693E+OlW 5.805&-OIH
4.019&-OfL
2*482E-
4.025E-Olt
OIL
I .669E-I-OOH
3.992E-OIL
t .23Sf:+OQW
4.913%.OIL
3 .S%E-
I .461E+QxJH
3.783E--0Il-I
4.033Ec-OiL
OIL
3.9?7E-OIM S,OJ5E--OIM
9*9GIE-OIW
S.O41E--01s
2.4?5&-OIL
4.0231’-
2*598E-OlH
4.024E-OLL
4*066E-OIW
3+579E-OIL
S.ZGbE--0iH
4.066E-OIL
3.39%-
3.575E--01L
2.6otE
OlL GlL
4.066E-
0%
Ott
4,00@E-OIL 3.938&-OIH
2,4836-OIL 6.3SSE-011%
3.52ZE+OOl-i
9.1&W--0lH
4,018E.-OIL
1 l343E+oOH
4.016E-OIL
334
WANG et
al.
TABLE
16510+9207
00.9
7’21
5G
HR
33.9
6’17
13325+3726
34.3
6,1X
57
HR 6469
05.0
1’21
17200+4001
05.2
1’17
58
HR
IS.5
0’43
19072+5220
15.5
0’42
59
HR
10.1
7’30
19301+5537
11.0
7’34
60
1411 216489
07.6
0’31
5110
7275
7428
22521+1640
ox.0
0’31
61
CF Tut
26.7
5’23
00515-7455
30.2
5’10
bS
HI)
18.2
3 40
17121-6653
11.0
3’38
70
39 Get
03.8
5’47
01140-0245
04.0
5’47
71
HI>
03.3
5’33
17340+7415
03.x
5’34
76
HD
15.2
1’27
155555
16053X
26337
04072-
0801
17.1
1’26
30.5
9’24
31 .6
9’25
46.3
5’54
47.1
6’01
5x.4
0’45
19369-0610
S7.6
0’52
HD
09.5
0’55
77
Ill)
7R
HD
79
III)
80
82
HD
83
84
37x47
05385-
2019
136905
15207-
0626
lY5SlO
190540
20031-
1850
09.0
O’S6
41.0
6’18
19346+2746
39.7
6’09
HD
19.7
9’19
01203+0709
20.6
9’30
HD
06.8
1’35
05.7
1’38
185151
8357
155638
17090+4901
2
(contd.)
6.245E+OOH
1.5S6E+OOH
5.4SSE-OIM
1.766E+OOH
5.45lE-OlH
4.026F.-IJIL
1.331E+OOH
3.539E-OIH
4.034E-OIL
2.330E+OOH
5.471E-01H
4.032E-OIL
1.918E+OOH
5.14bE-OlH
9.81oE-olH
2-.763E+OlH
7.179E+OOH
1.180E-kOOM
4.012E-011-1
2.47bE-OIL
4.030E-OIL
6.98@E-OlH
3.130E--0lL
4.0?3E-OIL
2.393E+OOH
6.525E-OIH
3.559E-OIL
1 .1631<+00H
3.01113-OlH
4.032t-
3.?45e--0111
IJli
4.ozot-011.
G .5lbl~-o1H
2.+B?E--OlL
4.026t-OIL
5.683E-OlH
3.717E-OlL
4.004E-OlL
,4.859E-0111
2.878F.-OlL
4.484E-OlL
3.455X-OIH
8.36lE-OIL
7.307E--01L
7.93lE-OIH
?.479E-OIL
6.310E-OIL
6.617E-OlH
3.569E-OIL
3.555E-OIL
2.974E-OlH
2.472E-OIL
4.098K-OIL
RS CVn Stars
I
rtar name
I E(V-J)
335
Infrared
Near Infrared Excess of RS CVn Syatcms
Table 3
NO.
in
I E(V-H)
I E(V-K)
NO.
star IIMC
E(V-J)
E(V--HI
W--K)
--
4
UX Ari
6
alpha Aur
-0.25
0.37
-0.14
0.74
15
RS cvn
-0.29
-0.02
24
AS Dra
-0.01
28.
2 Her
34
AR Lac
-0.04
40
AR Man
-0.93
1.74
0.93
42
LX Per
-0.14
0.11
0.13
43
sz Psc
-0.23
0 .oa
0.32
0.15
47
HR 1099
0.23
0.58
0.76
0.13
0.28
54
ER Vul
0.16
0.12
1 .92
1.93
55
HR 4665
-0.62
-0.66
-0.59
0.21
56
HR 5110
-0.19
-0.45
-0.60
-0.20
0.16 -0.5R
-1.07
excess was also confirmed by Verma’s But we must also point out observation [4]). that, for some systems such as AR Mon, HR 4665 and HR 5110, there is, in fact, an infrared “deficit”. This deficit, if verified by further observations would mean the presence of some “hot” regions, or the existence of some nonthermal source in the visible region.
Nr-----l
0.02
I theoretical values of the flux density at 12 urn were calculated from Kurucz’s model atmosphere [14] and the IRAS observed values were corrected for color [ll]. The results are shown in TABLE 4, and the histogram of E(V-[12]) is shown in Fig. 2. Again, a slight tendency towards positive values is shown; but apart from SZ Psc, the values differ little from measuring errors, hence, again, we cannot say that infrared excess is a general feature of RS CVn systems.
4
!lildbd 2
- 1.4,
0.2
-0.6
I.o
01
1.8
E (V-K)
Fig.
1
Histogram
of
Fig.
amongst the 40 RS CVn systems Similarly, that have been identified as IRAS sources, there are 10 with individual spectral Using classifications of the components. the same method, we discuss the colors (V-[12]), [12] representing the flux density at 12 Pm expressed in magnitudes. The
NO.
I
Star
Name
I
0.4
0 E (V-(12))
E(V-K)
Table
-0.4
4
SP.
Infrared Excw
I E(V-12)
2
Historgram
E(V-[12])
There is, statistically speaking, a slight excess in the (K-[12]) color. A possible explanation is interstellar reddening. As we did not correct for interstellar extinction, a small, statistical excess could well have been caused by interstellar reddening.
of RS CVn Syttcma_at 12pm II NO.
I Star
Name
SP.
I
-0.03
46
TY Py;
GS+GS
-0.01
47
HR 1099
GRV+KlIV
-0.01
of
0.02 -0.03
48
TZ Tri
GSIII+G5III
0.14
0.20
53
Eps UMi
DAB-
0.18
0.42
65
HD 155555
GSIV+KOV-IV
PO+G5III
0.28
WANG
336
5.
et al.
TWO-COLOR DIAGRAM
Discussion of the question of infrared excess is made difficult by the limited number of RS CVn systems with components having individual spectral types. To exploit the available data, we construct a two-color diagram using the flux densities at 25um, 12 urn,and 2.2pm, the last derived from the K magnitudes. For 21 RS CVn systems having the relevant data, we plot log(fzs/f12) against log(f12/f2_2) in Fig. 3. The solid line represents black body radiation. We note I
I
I
I
-0.6
-0.6
that all the observed points lie close to the black body line, in the region occupied by normal stars. Only 5 And and HR 5110 are somewhat peculiar. For 5 And, Johnson's measured K value is 1.52, [15], and if we use this value, the point (representedby an unfilled circle) will also fall in the region of normal star. For HR 5110, Verma [4] gave K= 3.53, and this would again be located in the normal region. Why, for those two stars, do our measurements differ from others by more than the measuring errors? Whether it is due to real changes in the infrared magnitudes, or some other cause must await further observation for elucidation. (Our measurement of 5 And was made at a phase of 0.47 and the possibility of effect of eclipse should not be excluded out of hand). Nevertheless, generally speaking, the RS CVn systems fall in the region of normal stars of the two-color diagram and we again have no reason to believe that infrared excess is a general characteristic of these systems.
z > - 1.0 < ,M
6.
We have discussed the near and middle infrared emission characteristics of RS CVn type close binaries. 3 out of 13, i.e. 23% show a color excess in the near infrared region. In the 12 urnregion, only 1 out of 12, or 10% does. so. Their positions on the infrared colorcolor diagram are all in the region of normal stars, showning that there is no circumstellar dust. Our conclusion therefore does not agree with Hall's statement that infrared excess is a general characteristic of RS CVn systems.
-1.2
- I.1
Fig. 3
CONCLUSION
Two-color diagram of 21 RS CVn systems
REFERENCES
[ll
Biermann, P. and Hall, D., IAU Symp., 73 (1975), 381 (1975), part I, 287. [31 HU Jing-yao, Pubz.Beijing Obs.S'uppl.5 (1983), 17.
[21 Hall, D., IAU Colloq., 29
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Vtrma.
[51
Bcrriman,
R.
161
Antonopoulou,
P. G.
et
al.,
hrophy~.
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et
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A~zron. SC;.,
97(1983), Sot.,
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205(1963),
67( 1960),
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469.
171
Antonopoulou,
E.,
Anron.
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Sup&
52(1963a),
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I61
An~~~opoulou,
E.,
Arrron.
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St&..
53~ 19831,),
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1963. 161 Ilrll, D., Private Communication, [91 Hall, D., Private Communication 1983. PO1 QIAN, ihong-yuet al. Act.Astrophys.Sin.5 (1985), 230. Glass, I.S., Mon.Not.R.Astron.Soc. 171 (1975), 19. R. I... .~l,rruph)r. J., Suppl. Ser.. 40, I. ;:t; k;lirucr, K~urrnnceI, Jul~nwn,
Ailron.
J., I.
H.
ct
al..
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128( 1963), Planetary
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