2 Observations

Table 1 lists all the available observation dates included in our analysis. Data collection on 57 Tau are spread over more than a decade. Besides a few hours of early observations, in which, the light variations were discovered, the first extended observations of 57 Tau were obtained by B.J. McNamara. This data set consists of 16 nights from 1981-83 and yielded 934 differential Strömgren b photometric measurements (68.9 hours) using the NMSU 16 inch telescope.

 

 

Table 1: The journal of observations. Four compact data sets exist

Date	HJD-	length	N	filter	Obs.
	2400000	(hours)
Oct. 25/26 1981	44903	5.4	87	b	BJM
Oct. 26/27 1981	44904	4.5	64	b	BJM
Nov. 1/2 1981	44910	4.1	60	b	BJM
Nov. 4/5 1981	44913	4.3	52	b	BJM
Nov. 9/10 1981	44918	5.7	69	b	BJM
Nov. 23/24 1981	44932	5.1	60	b	BJM
Nov. 24/25 1981	44933	5.2	65	b	BJM
Nov.30/Dec1 1981	44939	1.1	12	b	BJM
Dec. 7/8 1981	44946	5.4	70	b	BJM
Dec. 28/29 1981	44967	4.9	59	b	BJM
Jan. 25/26 1982	44995	3.7	46	b	BJM
Jan. 26/27 1982	44996	3.5	44	b	BJM
Feb. 15/16 1982	45016	2.7	34	b	BJM
Feb. 20/21 1982	45021	2.6	40	b	BJM
Jan. 3/4 1983	45338	5.6	83	b	BJM
Jan. 4/5 1983	45339	5.1	89	b	BJM
Dec. 14/15 1984	46049	4.3	86	V	MP
Sep. 19/20 1986	46693	3.1	70	V	MP
Sep. 20/21 1986	46694	1.6	29	V	MP
Oct. 18/18 1986	46722	3.6	68	V	MP
Nov. 28/29 1986	46763	6.0	106	V	MP
Nov. 29/30 1986	46764	4.7	90	V	MP
Nov. 30/Dec1 1986	46765	2.5	50	V	MP
Dec. 3/4 1986	46768	3.3	62	V	MP
Jan. 20/21 1987	46816	5.1	89	V	MP
Feb. 5/6 1987	46832	4.7	84	V	MP
Jan. 13/14 1989	47540	5.1	28	V	JSy, LZp
Jan. 14/15 1989	47540.9	5.9	39	V	JSy, LZp
Jan. 14/15 1989	47541.2	2.9	22	V	MP
Jan. 15/16 1989	47541.9	6.8	59	V	JSy, LZp
Jan. 16/17 1989	47542	5.4	43	V	JSy, LZp
Jan. 17/18 1989	47543	6.6	29	V	JSy, LZp
Jan. 18/19 1989	47544.9	3.6	33	V	JSy, LZp
Jan. 18/19 1989	47545.3	2.5	22	V	MP
Jan. 19/20 1989	47546.0	4.6	31	V	JSy, LZp
Jan. 20/21 1989	47546.9	6.6	60	V	JSy, LZp
Jan. 24/25 1989	47551	2.7	24	V	MP
Jan. 25/26 1989	47552	4.2	41	V	MP
Dec. 7/8 1989	47868	6.0	79	V	ZK
Dec. 8/9 1989	47869	7.2	117	V	ZK
Oct. 3 1995	49994	4.4	94	uvby	ER, MP
Oct. 5 1995	49996	4.2	75	uvby	ER, MP
Oct. 6 1995	49997	5.4	73	uvby	ER, MP
Oct. 7 1995	49998.4	1.5	23	uvby	ER, MP
Oct. 8 1995	49999.4	5.9	100	uvby	ER, MP
Oct. 8 1995	49999.9	2.9	41	uvby	GB
Oct. 9 1995	50000.4	5.0	85	uvby	ER, MP
Oct. 9 1995	50000.8	2.6	25	uvby	GB
Oct. 10 1995	50001	5.2	178	uvby	ER, MP
Oct. 12 1995	50003	1.4	21	uvby	GB
Oct. 13 1995	50004	2.4	32	uvby	GB
Oct. 14 1995	50005	5.2	84	uvby	AR
Oct. 15 1995	50006	4.9	79	uvby	AR
Oct. 16 1995	50007	3.3	38	uvby	GB
54 nights		232.2	3243

Apart from the single night in 1984, 57 Tau has been regularly observed, by M. Paparó, from the Konkoly Observatory in the 1986/87 season, and Johnson V colour data were obtained over a 38.9 hour during 9 nights.

Two coordinated observing campaigns were organized by M. Paparó in 1989, including Chinese and Hungarian observatories, and in 1995 which included Spanish, Mexican, Chinese and Hungarian observers. Unfortunately weather conditions in China and Hungary were poor in 1995, so no usable data were obtained.

The Chinese observations were obtained at the Xinglong Station of Beijing Astronomical Observatory on the 60 cm reflector with a classical single channel photoelectric photometer through a Johnson V filter. Over 8 nights, 45 hours of observations were collected by Jiang Shi-yang and Li Zhi-ping.

As a consequence of bad weather, only 4 nights (12.9 hours) were obtained by M. Paparó during the coordinated campaign in early 1989.

Two additional nights (13.1 hours) were obtained by Z. Kolláth at Konkoly Observatory at the end of 1989. All the Hungarian observations were obtained on the 0.5 m reflector of Piszkéstetö, the mountain station of Konkoly Observatory, through a V filter close to the Johnson UBV system. A single channel integrating photometer, developed and build by Géza Virághalmy, the technical deputy director of Konkoly Observatory, was equipped with an EMI 9502S photomultiplier. The photometer is characterized by high instrumental zero-point stability.

In 1995, 7 nights of observations (31.6 hours) were collected in Spain by E. Rodriguez and M. Paparó and 2 nights (10.1 hours) by A. Rolland. The 0.90 m telescope at Sierra Nevada, with the six-channel Danish photometer, was used for obtaining Strömgren uvby colours.

Five nights of observations (12.5 hours) were obtained by S.F. Gonzalez-Bedolla on the 1.5 m telescope at San Pedro Martir in Mexico. Simultaneous Strömgren uvby data were collected with a Danish photometer.

Altogether, 232 hours of data obtained on 54 nights at different sites are included in our comprehensive analysis on 57 Tau. All observations were obtained as differential measurements, so variable, comparison and sky background were measured alternately. Except for the multi-site campaign in 1995, the only comparison star generally used was HR 1358 (= HD 27483). The analysis of the errors and/or noise effects and/or instrumental effects could not be done for most part of the data set as in the case of two comparison stars. In the course of the multi-site campaign in 1995 a second comparison star, HR 1430 (= HD 28556), was also observed, to check the constancy of the primary comparison star.

Reductions were independently made by the observer for each data set. In principle, this could introduce instrumentation effect in the whole set, especially at low frequencies. The standard method of differential extinction corrections was applied. In most cases, nightly extinction coefficients were used, in other cases, mean values of the extinction coefficients for a given site were accepted.

The accuracy of the observations are not homogeneous, specifically the data collected in the coordinated 1989 campaign from China and Hungary have larger scatter. To compensate for this, sequences of three observations were combined for the Chinese data compared to the light curves published by Fu et al. ([1996]). A similar process involving the averaging of 2 points was used for the Hungarian data obtained at the beginning of 1989. The impression that the light curves consist of poor quality data, which comes from the low signal/noise value, is a consequence of the low amplitude light variability of 57 Tau. The accuracy of a single measurement, given below, is similar to that usually obtained for $\delta$ Scuti-type stars.