Appendix C: Strömgren $\vec{uvby\beta}$ photometry of HD 153919/4U1700-37

Figure C.1: Strömgren uvby photometry, the derived colours m1 and c1, and the $\beta$ parameter (see text) for HD 153919/4U1700-37. The $uvby\beta$ are presented differentially with respect to the comparison star HD 154368. Mean levels are represented by dotted lines.

In August 1993 we obtained Strömgren uvby plus broad and narrow band H$\beta$ photometry using the 50 cm SAT at ESO/La Silla. The O9.5 Iab star HD 154368 was measured for comparison. The photometry is presented in Tables C1 and C2. The magnitude differences between HD 153919/4U1700-37 and HD 154368 are plotted in Fig. C.1, together with the colours m₁ and c₁ for HD 153919/4U1700-37 as described in Sterken et al. (1995). The comparison star did not vary with time. The standard deviation for each individual measurement is typically 0.005 mag in u and y, and 0.004 mag in v and b. From the scatter on small orbital phase scales in the resulting lightcurves a formal, conservative estimate of 1- $\sigma \sim0.01$ mag is derived. Because of the advantages of the multi-channel photometer, the errors in m₁ and c₁ are smaller than this. The standard deviation of the distribution of measured values gives an upper limit to the error on each individual measurement of 1- $\sigma=0.0065$ mag for both colours. The $\beta$parameter is derived from the H$\beta$ narrow- and wide-band magnitudes. It increases with increasing absorption strength of the H$\beta$ line. The data give an upper limit to the error in $\beta$ of 1- $\sigma=0.0019$ mag.

 

 

Table C.1: Heliocentric Reduced Julian Date ${\textit {\rm RJD}}_\odot$ = JD-2449200, u, v, b and y magnitudes (with their standard deviation of the last digit(s) within parentheses) and $\beta$ parameter of HD 153919/4U1700-37. Orbital phases may be calculated from: $\phi _0 \equiv$ JD 2446161.3400(30); $P=3{\hbox{$.\!\!^{\rm d}$ }}411652(26)$ (Haberl et al. 1989). The last row gives the mean values and their 1-$\sigma$ errors.

${\textit {\rm RJD}}_\odot$	u ( ${\sigma}_u$)	v ( ${\sigma }_v$)	b ( ${\sigma}_b$)	y ( ${\sigma}_y$)	$\beta$
09.6414	7.172(4)	7.071(3)	6.772(3)	6.584(4)	1.230
13.6344	7.153(4)	7.048(2)	6.751(2)	6.564(3)	1.249
14.6736	7.130(4)	7.023(3)	6.730(3)	6.544(4)	1.516
15.6159	7.086(2)	6.987(4)	6.695(3)	6.506(4)	1.195
16.6497	7.182(5)	7.078(3)	6.780(3)	6.595(5)	1.380
17.6424	7.101(5)	6.995(4)	6.703(4)	6.515(4)	1.352
18.5755	7.177(6)	7.067(4)	6.771(5)	6.594(6)	1.096
19.6214	7.114(5)	7.011(3)	6.717(3)	6.534(3)	1.268
20.6311	7.137(7)	7.036(4)	6.743(4)	6.556(4)	1.335
21.5959	7.155(3)	7.051(3)	6.755(3)	6.566(4)	1.183
22.5641	7.129(3)	7.025(2)	6.731(3)	6.541(3)	1.096
23.5721	7.187(7)	7.084(5)	6.784(4)	6.595(4)	1.124
24.5867	7.132(4)	7.025(4)	6.728(2)	6.539(3)	1.180
25.5770	7.183(7)	7.089(8)	6.787(8)	6.597(12)	1.158
26.5891	7.161(8)	7.052(3)	6.754(2)	6.566(5)	1.212
28.5688	7.141(3)	7.044(6)	6.748(7)	6.560(7)	1.159
32.5778	7.143(6)	7.042(3)	6.745(3)	6.554(3)	1.236
Aug.93	7.146(7)	7.043(7)	6.747(7)	6.559(7)	1.233(27)

 

 

Table C.2: Same as Table C.1, but now for the comparison star HD 154368.

${\textit {\rm RJD}}_\odot$	u ( ${\sigma}_u$)	v ( ${\sigma }_v$)	b ( ${\sigma}_b$)	y ( ${\sigma}_y$)	$\beta$
09.6355	7.224(4)	6.962(2)	6.600(2)	6.151(2)	1.197
09.6475	7.224(4)	6.959(3)	6.598(2)	6.150(4)	1.250
13.6283	7.210(3)	6.946(2)	6.585(3)	6.139(2)	1.214
13.6405	7.207(5)	6.946(3)	6.584(2)	6.140(3)	1.271
14.6676	7.188(4)	6.928(3)	6.566(3)	6.124(3)	1.463
14.6795	7.186(7)	6.929(3)	6.567(3)	6.124(3)	1.566
15.6101	7.215(9)	6.949(5)	6.587(5)	6.139(3)	1.165
15.6237	7.207(4)	6.947(3)	6.583(2)	6.138(3)	1.219
16.6434	7.189(11)	6.927(5)	6.562(5)	6.116(5)	1.334
16.6560	7.182(4)	6.924(4)	6.560(5)	6.116(5)	1.418
17.6364	7.183(5)	6.918(4)	6.558(4)	6.112(4)	1.310
17.6484	7.177(6)	6.920(4)	6.558(4)	6.117(4)	1.384
18.5696	7.203(5)	6.931(4)	6.575(4)	6.142(5)	1.075
18.5832	7.209(6)	6.940(4)	6.582(4)	6.148(4)	1.107
19.6155	7.193(33)	6.933(8)	6.570(8)	6.127(6)	1.232
19.6283	7.185(6)	6.926(6)	6.567(5)	6.123(6)	1.296
20.6244	7.199(6)	6.933(4)	6.572(4)	6.126(4)	1.291
20.6374	7.192(6)	6.933(5)	6.572(4)	6.127(5)	1.368
21.5897	7.198(3)	6.939(2)	6.575(3)	6.127(3)	1.153
21.6021	7.206(6)	6.939(6)	6.575(5)	6.127(5)	1.199
22.5579	7.198(4)	6.935(3)	6.572(2)	6.124(2)	1.074
22.5707	7.195(3)	6.938(3)	6.574(3)	6.129(3)	1.104
23.5659	7.204(6)	6.938(5)	6.577(4)	6.129(4)	1.099
23.5784	7.197(4)	6.939(3)	6.576(3)	6.132(4)	1.134
24.5792	7.215(3)	6.956(2)	6.594(2)	6.148(3)	1.146
24.5931	7.213(4)	6.952(3)	6.592(2)	6.145(5)	1.197
25.5690	7.234(9)	6.972(7)	6.607(7)	6.158(7)	1.124
25.5837	7.236(12)	6.987(15)	6.622(15)	6.182(18)	1.172
26.5828	7.241(8)	6.975(5)	6.611(4)	6.161(4)	1.179
26.5956	7.230(6)	6.970(3)	6.607(3)	6.162(5)	1.231
28.5619	7.206(11)	6.948(4)	6.584(4)	6.137(4)	1.128
28.5756	7.204(4)	6.945(2)	6.582(2)	6.137(3)	1.173
32.5704	7.224(6)	6.969(4)	6.607(4)	6.164(6)	1.196
32.5859	7.210(8)	6.951(6)	6.589(7)	6.146(6)	1.266
Aug.93	7.205(3)	6.944(3)	6.582(3)	6.137(3)	1.228(20)

Our uvby lightcurves of HD 153919/4U1700-37 agree with the lightcurves obtained by Hammerschlag-Hensberge & Zuiderwijk (1977). They noticed an orbital modulation of the colour m₁, with a minimum at $\phi\sim0.2$, and suggested that this might be caused by variability in the emission lines of He  II 4686, C  III 4650 and N  III 4634-4641 that are included in the Strömgren b-filter. Our observations indeed confirm a minimum in m₁between $\phi=0.1$ and 0.2. Krzeminski (1976) did not find any orbital modulation of the He  II 4686 line. Kaper et al. (1994) found variability in the He  II 4686 line profile, but this alone cannot cause observable variability in the Strömgren b-filter. The other two mentioned emission lines may still be variable.

There is a weak indication for a gradual decrease in the H$\beta$ absorption (or an increase in emission) towards $\phi=1$, possibly with a secondary weak minimum around $\phi=0.3$ (Fig. C.1). This is exactly what Kaper et al. (1994) found in their study of the variability in the H$\beta$ P-Cygni line profile. They attributed this to the presence of a photo-ionization wake.