Praesepe

   
3 Observations

The participating observatories (Table 1) represent a large diversity of telescope sizes and of instrumentation both in terms of resolution and efficiency.

 

 

Table 1: Sites participating in the spectroscopic campaign. The name abbreviations stand for Nordic Optical Telescope, Thüringer Landessternwarte, Okayama Astrophysical Observatory, Vainu Bappu Observatory, McDonald Observatory. D is telescope aperture diameter in meters, E- means echelle spectrograph in either Cassegrain (Cs) or Coudé (Co) focus.

Name	Location	D	Inst.	R	Observers
NOT	Canary I.	2.54	E-Cs	4300	Dall
TLS	Germany	2.0	E-Co	20000	Lehman
OAO	Japan	1.88	Co	12000	Kambe,
					Fukata, Nagae
VBO	India	2.3	Cs	130	Anupama
McD	Texas	2.1	E-Co	45000	Handler,
					Horner

Details of the observations conducted at each site are given below. Table 2 gives a log of the observations.

 

 

Table 2: Log of the observations. See caption of Table 1 for the abbreviations.

UT Day of	Site	Length	No. of
Feb. 98		(hours)	spectra
3.81	TLS	7.0	60
4.82	TLS	7.7	92
11.74	VBO	3.3	23
11.89	NOT	7.3	105
12.69	OAO	2.0	17
12.72	VBO	2.3	19
13.09	McD	6.7	83
13.42	OAO	6.0	58
13.84	NOT	6.5	57
14.80	TLS	0.8	10
15.25	McD	1.0	18
15.51	OAO	6.8	66
15.84	NOT	8.4	91
16.20	McD	0.3	7
16.56	OAO	4.8	49
16.83	NOT	8.6	101
17.07	McD	1.7	21
17.41	OAO	8.3	78
17.87	NOT	9.3	95
18.06	McD	7.7	91
18.76	TLS	7.0	84
In total:		113.5	1225

Nordic Optical Telescope

7 nights from 11 to 17 February, with the nights of 12th and 14th lost entirely due to bad weather. A total of 449 echelle spectra in 41.5 hours were taken with exposure times between 180 and 300 s, most frequently around 240 s. The spectra were obtained with the ALFOSC instrument, covering 6 partially overlapping orders including H$\alpha$ and H$\beta$. Due to the long readout time of the full CCD ($\sim$80 s) the frames were windowed as tightly as possible, with the side effect that the overscan strip information was lost.

The data are of high quality and provide the backbone of the data set.

Thüringer Landessternwarte

The 2 meter telescope with echelle spectrograph at Coudé focus observed on the nights of 3, 4, 14, and 18 February for a total of 22.5 hours, giving a total of 246 echelle spectra. Time sampling was 300 s on most nights (420 s on February 3).

Good quality data with a clear oscillation signal in  $\Lambda ^{{\rm H}\alpha }$.

Okayama Astrophysical Observatory

268 spectra were obtained over a total of 28.1 hours. Integration times were about 300 s. The observations ran from 12 to 17 February with the night of the 14th lost to bad weather.

Two different slit widths were used, giving resolutions of 12500 and 10200 respectively. The spectra have quite low S/N due to the combination of high resolution and short exposures, but nevertheless the oscillation signature is found to be present in the set.

Vainu Bappu Observatory

10 to 12 February with the 10th being completely cloudy. With a total observing time of 5.4 hours, 42 spectra were obtained with the OMR spectrograph (Prabhu et al. 1998). From this site some two hours were also spent on BV Cnc. Sampling interval was between 300-420 s.

The data are of good quality with a clearly visible oscillation signal in $\Lambda ^{{\rm H}\alpha }$ despite the short series.

McDonald Observatory

12 to 17 February with plenty of bad weather. When it was possible to observe it happened mostly through clouds with resulting bad S/N. The data consists of high resolution echelle spectra, unfortunately with very low throughput, which further diminished the count rate. Despite of this, the oscillation pattern is recognised in the data.

3.1 Summary of observations

In general all sites collected high quality data despite the poor weather conditions. Especially the large gap between February 4th and 10th is unfortunate, but not critical. Even with spectra of such varying characteristics, the oscillation signal known to be present in BN Cnc is detected in all the individual data sets, although in some cases with very low S/N.

Praesepe