2. Observations

  An extensive campaign of monitoring II Peg was organised in the third quarter of 1992. The core of the coordinated campaign took place during the two-week interval 5-19 September, but photometric observations were also made in both July and August to establish the phase and amplitude of the spot modulation prior to the main phase of the campaign.

2.1. Photometry

  Visible and infra-red photometry was carried out at a number of observing sites between July and September 1992. Standard photometry in Johnson UBV (Johnson 1966), Cousins (Cousins 1976) and infra-red JHK (Johnson 1966) as well as continuous monitoring for flares in the Johnson U band were achieved.

2.1.1. Photometry - Jacobus Kapteyn Telescope (JKT)

  We observed II Peg at the 1m JKT at the Observatorio del Roque de los Muchachos on the island of La Palma in the Canary Islands, 7-16 September 1992. The telescope was equipped with an EEV 12801180pxl CCD detector and glass filters, which together approximated to the Cape photometric system. Equatorial standard stars from the lists of Menzies et al. (1991) were measured on each night to relate the instrumental to the standard system. The resulting magnitudes and colours are to be found in Table 1 (click here).

IIPeg, along with two nearby comparison stars, viz. SAO91568 (= BD+284665) and SAO91577 (= HD224085 = BD+284667), were measured in all five colours several times per night. These acted as comparison and check star, respectively. Their mean magnitudes and colours were found to be
SAO91568: V = 8.507; (B-V) = 0.751; (U-B) = 0.474
;
SAO91577: V = 8.243; (B-V) = 1.267; (U-B) = 1.420 ; .
The values for SAO91577 may be compared with those determined by the present authors over several seasons (Rodonó et al. 1986; Andrews et al. 1988; Byrne et al. 1989; Doyle et al. 1989a, 1992a), viz.
SAO91577: V = 8.23; (B-V) = 1.29; (U-B) = 1.41
;
and with those found from our other photometry below.

Continuous monitoring of II Peg in the Johnson U band was also undertaken at the JKT on 8 nights between 6/7-15/16 September 1992 (Byrne et al. 1994). The telescope was moved between individual exposures to create up to ten images of the star before reading out the CCD, thus reducing the overhead due to CCD readout. Details of the coverage achieved, which totalled 31.7 hr, will be found in Table 2 (click here). No flares were recorded in this time.

 

Date UT JD Phase V B-V U-B V-R V-I

1992 2440000.0+ Jacobus Kapteyn Telescope

08 Sep 23:52 8874.4945 0.655 7.522 1.022 0.798 0.599 1.220

09 Sep 05:28 8874.7277 0.689 7.500 1.022 0.877 0.645 1.275

10 Sep 02:13 8875.5923 0.818 7.510 1.017 0.628 0.603 1.268

23:58 8876.4985 0.953 7.599 1.058 0.707 0.613 1.266

12 Sep 00:15 8877.5104 0.103 7.597 1.012 0.704 0.561 1.269

13 Sep 02:18 8878.5957 0.265 7.456 1.042 0.650 0.594 1.206

14 Sep 00:02 8879.5017 0.400 7.437 1.029 0.698 0.563 1.203

15 Sep 00:14 8880.5095 0.549 7.457 1.055 0.669 0.577 1.235

16 Sep 00:50 8881.5345 0.702 7.444 0.980 0.793 0.587 1.235

17 Sep 05:11 8882.7158 0.877 7.624 1.105 0.828 0.632 1.278 Stephanion Observatory

25 Jul 00:37 8828.526 0.818 7.551 1.050 0.727

27 Jul 00:34 8830.527 0.116 7.571 1.045 0.731

28 Jul 00:39 8831.527 0.265 7.484 1.021 0.740

29 Jul 00:41 8832.528 0.413 7.494 1.035 0.760

30 Jul 00:39 8833.527 0.562 7.500 1.033 0.717

31 Jul 00:42 8834.529 0.711 7.478 1.037 0.621

31 Jul 23:42 8835.488 0.854 7.563 1.047 0.706

03 Sep 21:58 8869.415 0.899 7.552 1.052 0.710

04 Sep 22:26 8870.435 0.051 7.646 1.058 0.739

05 Sep 21:05 8871.378 0.191 7.496 1.008 0.468

09 Sep 01:46 8874.574 0.666 7.462 1.016 0.652

11 Sep 01:29 8876.562 0.962 7.608 1.049 0.717

18 Sep 22:05 8884.420 0.131 7.630 1.047 0.726 Bulgarian National Observatory

26 Aug 01:23 8860.558 0.582 7.522 1.031 0.671

27 Aug 00:56 8861.539 0.728 7.497 1.030 0.653

28 Aug 00:32 8862.522 0.874 7.560 1.027 0.656

29 Aug 00:04 8863.503 0.020 7.652 1.057 0.704

30 Aug 00:42 8864.529 0.173 7.571 1.043 0.692

30 Aug 22:15 8865.427 0.306 7.518 1.036 0.694

Table 1: Table of standard magnitudes and colours of II Peg derived from observations taken at Observatorio del Roque de los Muchachos in September 1992, at the Stephanion Observatory in both July and September 1992 and at the Bulgarian National Observatory in August 1992. Phases have been calculated according to the ephemeris of Vogt (1981), i.e.  

 

Date Monitoring Intervals Total

1992 UT Jacobus Kapteyn Telescope

6/7 Sep. 04:49-06:07

7/8 Sep. 03:53-05:17

8/9 Sep. 20:33-20:36 20:42-23:26 03:57-05:02

10/11 Sep. 20:55-23:11

12/13 Sep. 02:52-06:01

13/14 Sep. 20:25-23:46 01:32-06:10

14/15 Sep. 21:01-23:20 01:58-06:08

15/16 Sep. 21:01-23:34 03:00-05:59 Stephanion Observatory

4/5 Sep. 22:24-23:55 00:11-01:36 01:52-02:35

5/6 Sep. 19:41-20:42 21:27-23 43

00:00-01:04 01:10-01:46

6/7 Sep. 19:49-21:19 21 23-22:06

22:16-01:18 01:29-01:38

7/8 Sep. 20:03-23:36 23:40-01:48 01:56-02:22

8/9 Sep. 19:53-22:19 22:27-23:14

23:23-23:55 23:59-00:14 00:18-01:31

9/10 Sep. 19:38-21:55 22:01-22:36 22:40-22:50

10/11 Sep. 20:16-01:11

11/12 Sep. 19:48-22:40 22:46-01:14 01:22-02:17

12/13 Sep. 19:09-19:57 21:23-02:26

13/14 Sep. 18:52-19:46 19:50-20:07

20:17-22:28 22:33-00:33

00:37-01:14 01:23-02:23

14/15 Sep. 20:47-00:29 00:39-01:21 01:34-02:31

15/16 Sep. 18:49-20:04 20:25-22:38 22:43-02:19

16/17 Sep. 18:48-20:00 21:14-22:05

22:09-23:06 23:16-01:10 01:29-02:20

17/18 Sep. 19:03-19:51 20:01-01:33 01:51-02:18

18/19 Sep. 20:15-21:41 22:27-01:46

Table 2: Flare monitoring times of II Peg at the Jacobus Kapteyn Telescope, 6-16 September 1992, and at Stephanion Observatory, 4-19 September 1992. Breaks of duration 3min have been ignored. Times in bold are those during which both telescopes were observing for at least some of the time 

2.1.2. Photometry - Stephanion Observatory

  Standard UBV photometry and U-band flare monitoring were carried out at the Stephanion Observatory (SO), Greece, using the 75cm Cassegrain reflector belonging to the University of Thessaloniki between July24-31 and September3-18, 1992. The telescope and photometer have been described by Mavridis et al. (1982). Nightly measurements were referred to the same two local comparison stars, i.e. SAO91568 and SAO91577, which in turn were referred to standard stars on the best 3 nights photometrically. Typical errors in V and B-V were 0.01, while those for U-B were 0.04. The following mean magnitudes and colours for these local comparisons were derived.
SAO91568:   V = 8.525; (B-V) = 0.781; (U-B) = 0.453
SAO91577:   V = 8.246; (B-V) = 1.253; (U-B) = 1.239.
These may be compared with our magnitudes for these same stars as measured at the JKT above (see Sect. 2.1.1 (click here) and Sect. 3.1.1 (click here)). The resulting magnitudes and colours derived for II Peg will be found in Table 1 (click here).

Continuous monitoring of II Peg in the Johnson U band was also undertaken at Stephanion on 15 nights between 4-19 September 1992. Details of the coverage achieved, which totalled 76.2 hr, will be found in Table 2 (click here).

2.1.3. Photometry - Bulgarian National Observatory

  Standard UBV photometry was also carried out at the Bulgarian National Observatory's (BNO) 60cm telescope at Rozhen between 25-30 August 1992. These observations were made differentially with respect to the local comparison star, SAO91568, for which the standard magnitudes and colours measured previously were also assumed here as follows.
SAO91568:   V = 8.54; (B-V) = 0.79; (U-B) = 0.49.
The resulting magnitudes and colours derived for II Peg will be found in Table 1 (click here).

2.1.4. Photometry - Infra-red

  Infra-red photometry of II Peg was carried out using the 1.5 m Carlos Sanchez telescope at the Observatorio del Teide of the Instituto de Astrofisica de Canarias (IAC) at Mt. Teide, Tenerife (Canary Islands) on 13 nights between 30 July and 14 August 1992. A CVF photometer with a focal plane chopper was used. The detector was a liquid-nitrogen-cooled InSb device which, together with filters, gave a good approximation to the standard J, H and K bands (Johnson 1966; Glass 1985). Both the chopping amplitude and the aperture diameter were 15 arcsec. Each photometric measurement was performed exposing the star for 10 s in alternate beams until the signal-to-noise of the integrated measurement was 500. The comparison star was SAO91577. Its standard magnitudes were found to be
SAO91577:   J=6.15;  H=5.84;  K=5.32;  L=5.17.
Standard errors on each measurement were 0.01.

Standard reference stars were also observed to calibrate the observations to the standard system. A log of this data will be found in Table 3 (click here).

 

Date UT JD Phase J H K

1992 2440000.0+

31 Jul. 04:20 8834.681 0.734 5.412 4.802 4.628

 1 Aug. 03:23 8835.641 0.876 5.411 4.802 4.623

 2 Aug. 03:39 8836.652 0.027 5.455 4.842 4.662

 3 Aug. 02:54 8837.621 0.171 5.419 4.803 4.627

 5 Aug. 01:26 8839.560 0.459 5.407 4.788 4.599

 6 Aug. 03:00 8840.625 0.618 5.392 4.775 4.597

 7 Aug. 02:42 8841.612 0.765 5.400 4.782 4.604

 8 Aug. 00:41 8842.528 0.901 5.452 4.821 4.650

 9 Aug. 00:48 8843.533 0.050 5.441 4.811 4.642

10 Aug. 03:21 8844.640 0.215 5.389 4.786 4.620

11 Aug. 02:35 8846.607 0.507 5.395 4.780 4.605

12 Aug. 03:51 8847.660 0.664 5.389 4.766 4.599

15 Aug. 04:40 8850.694 0.115 5.441 4.825 4.649

Table 3: Table of nightly mean standard J, H and K magnitudes of II Peg derived from the observations taken at the Observatorio del Teide, Tenerife, in July and August 1992. Phases have been calculated according to the ephemeris of Vogt (1981), i.e.  

2.2. Optical spectroscopy

  Three optical spectroscopic data sets were taken during the campaign. The first consisted of high-resolution spectra, one per night, of Balmer H and H, as well as HeI D. The second was in the blue at lower resolution and included the higher members of the Balmer series and the CaII H&K doublet. The third comprised a time sequence of H spectra, also at a lower resolution.

2.2.1. Optical spectroscopy - high-resolution data

High-resolution () spectroscopy was carried out using the Solar Stellar Spectrograph at the US National Solar Observatory's 1.6m McMath Pierce Telescope at Kitt Peak, Arizona on 5 nights between 11-16 September 1992. On all clear nights a single spectrum was recorded in the region of the Balmer H line, while on a smaller number of nights spectra were recorded near Balmer H and HeID. A log of these spectra will be found in Table 4 (click here).

 

Date UT Exp JD Phase

1992 mid-exp min 2440000.0+ Å McMath Pierce Telescope

11 Sep. 04:57 30 8876.706 0.983 6562.8

06:55 30 8876.788 0.996 5975.7

08:52 30 8876.869 0.008 4861.3

12 Sep. 08:47 40 8877.866 0.156 6562.8

09:57 30 8877.915 0.163 4861.3

11:39 35 8877.985 0.174 5975.7

14 Sep. 08:47 30 8879.866 0.453 6562.8

10:04 35 8879.919 0.461 5975.7

15 Sep. 08:35 40 8880.858 0.601 6562.8

16 Sep. 08:28 07 8881.853 0.749 6562.8 Isaac Newton Telescope

15 Sep. 02:00 20.0 8880.583 0.560 4128

16 Sep. 01:56 16.7 8881.581 0.708 4128

17 Sep. 02:00 16.7 8882.583 0.858 4128

18 Sep. 02:01 16.7 8883.584 0.006 4128

20 Sep. 01:56 16.7 8885.581 0.303 4128

Table 4: A log of the optical high-resolution spectra recorded at the McMath Pierce Telescope between 11-16 September and of blue low-resolution spectra at the Isaac Newton Telescope between 14-19 September 1992. Phases have been calculated according to the ephemeris of Vogt (1981) 

2.2.2. Optical spectroscopy - blue low-resolution data

Low-resolution () spectroscopic data in the blue region () were obtained using the Intermediate Dispersion Spectrograph (IDS) on the 2.5 m Isaac Newton Telescope (INT) at the Observatorio del Roque de los Muchachos on the island of La Palma on five nights between 1992 September 14-19. A 2400 lines/mm grating, blazed at 3500 Å was used and a slit width of 1.35 arcsec, which projected to 2.2 pxl on the CCD detector. A log of these spectra will be found in Table 4 (click here).

2.2.3. Optical spectroscopy - red low-resolution data

Low-resolution () H data were recorded on 9 nights between 7-20 September 1992 using the 40 cm telescope at the University of Birmingham's Wast Hills Observatory. The telescope was equipped with a zoom lens spectrograph (Elliott 1996) equipped with a GEC CCD detector which gave 385 pixels in the dispersion direction, corresponding to a wavelength coverage of . A log of this data will be found in Table 5 (click here).

 

Date UT JD Phase

1992 2440000.0+

7/8 Sep. 21:53-04:35 8873.412-.691 0.494-0.535

8/9 Sep. 20:47-22:31 8874.366-.483 0.635-0.653

10/11 Sep. 21:39-01:32 8876.402-.564 0.938-0.962

11/12 Sep. 20:38-01:12 8877.360-.550 0.081-0.109

13/14 Sep. 20:16-04:16 8879.343-.678 0.376-0.425

14/15 Sep. 20:04-02:35 8880.336-.608 0.523-0.564

15/16 Sep. 23:54-04:49 8881.496-.701 0.696-0.726

16/17 Sep. 20:09-21:22 8882.340-.390 0.821-0.829

20/21 Sep. 20:30-21:26 8886.353-.393 0.418-0.424

Table 5: A log of the optical low-resolution H spectra recorded at the University of Birmingham's Wast Hills Observatory between 7-20 September 1996. Phases have been calculated according to the ephemeris of Vogt (1981) 

2.3. UV spectroscopy

  Ultraviolet spectroscopy was obtained with the International Ultraviolet Explorer satellite (IUE) (Boggess et al. 1978) on 12 consecutive days between 1992 September 5-16. Data were obtained using both the IUE's long-wavelength (; LWP) and short-wavelength (; SWP) cameras in high- ( at ; HIRES) and low-resolution ( at ; LORES), respectively. Between three and six spectra were obtained on each date alternating between LWP HIRES and SWP LORES. This observing scheme enabled us to make maximum use of the satellite as SWP exposures were made while the LWP camera was being read to ground and prepared for the next observation and vice versa. A log of the spectra will be found in Table6 (click here).

 

Date IUE Image UT Exp. JD (mid-exp)

1992 No. Start min. 2440000.0+

5 Sep. SWP45531 19:40:33 20 8871.327

LWP23854 20:19:41 30 8871.357

SWP45532 20:58:30 107 8871.411

6 Sep. LWP23864 19:37:39 30 8872.328

SWP45543 20:17:32 100 8872.380

LWP23865 22:06:18 30 8872.431

7 Sep. LWP23873 19:20:32 30 8873.316

SWP45553 19:59:17 100 8873.418

LWP23874 21:47:16 30 8873.368

SWP45554 22:22:56 25 8873.441

8 Sep. LWP23875 15:51:00 30 8874.171

SWP45571 16:28:51 100 8874.221

LWP23876 18:23:12 30 8874.277

SWP45572 19:02:56 100 8874.328

LWP23877 20:53:37 30 8874.381

SWP45573 21:33:38 74 8874.424

9 Sep. LWP23888 20:04:23 30 8875.347

SWP45586 20:42:53 100 8875.398

LWP23889 22:28:15 18 8875.443

10 Sep. SWP45595 19:47:17 30 8876.335

LWP23898 20:33:49 100 8876.392

SWP45596 22:19:30 28 8876.440

11 Sep. SWP45599 19:54:49 30 8877.340

LWP23907 20:32:13 100 8877.390

SWP45600 22:19:41 28 8877.440

12 Sep. SWP45617 20:00:03 30 8878.344

LWP23912 20:35:24 60 8878.379

SWP45618 21:50:47 60 8878.431

13 Sep. SWP45625 20:05:19 30 8879.347

LWP23923 20:51:21 60 8879.390

SWP45626 21:58:12 50 8879.433

14 Sep. SWP45642 19:23:44 30 8880.319

LWP23938 20:06:15 60 8880.359

SWP45643 21:15:08 94 8880.418

15 Sep. SWP45651 19:01:52 30 8881.303

LWP23945 20:41:13 60 8881.383

SWP45652 21:49:48 60 8881.430

16 Sep. SWP45660 19:58:31 30 8882.343

LWP23958 20:43:58 60 8882.385

SWP45661 21:52:25 55 8882.430

Table 6: Log of the IUE spectra of IIPeg obtained between 1992 September 5-16. Phases have been calculated according to the ephemeris of Vogt (1981) 

2.4. Microwave observations

  II Peg was also monitored between 7-15 September 1992 using the Broad-band Interferometer (BBI) (Padin et al. 1987) at the Nuffield Radio Astronomy Laboratory (NRAL) at Jodrell Bank, England. The BBI operates at 5 GHz () with a bandwidth of 384 MHz and has a sensitivity of .

The observations consisted of single scans of the source, each nominally 45 min but, due to telescope tracking errors (due, in turn, to high winds), actually achieved a typical on-source integration time of . Individual integrations each lasted 20 s. After averaging these 20 s integrations over a scan the typical noise level was .

The BBI was on 24 hr scheduled operation observing a number of objects including II Peg. Amplitude calibrators, 3C 48 and 3C 286, were observed every . Their flux densities were taken as 5.335 Jy and 7.338 Jy respectively (Baars et al. 1977). A nearby object, 2004+403, was chosen as a phase calibrator with an observing cycle of 15 minutes on phase calibrator and 45 minutes on II Peg (referred to as a scan). A tracking window of 3 arcmin was imposed which rejected the incoming data when the observing source fell outside this window due to tracking error.

Details of the coverage achieved will be found in Table 7 (click here).

 

Day UT JD Flux Day UT JD (mid-exp) Flux

1992 (mid-exp) mJy mJy 1992 2440000.0+ mJy mJy 2440000.0+

7 Sep. 17:35-18:00 8873.241 2.5 0.5 10 Sep. 18:18-19:00 8876.277 1.111 0.4

7 Sep. 18:24-19:00 8873.279 2.7 0.5 10 Sep. 19:19-20:00 8876.319 2.584 0.5

7 Sep. 19:19-20:00 8873.319 1.9 0.4 10 Sep. 20:19-21:00 8876.361 2.485 0.5

7 Sep. 20:18-21:00 8873.360 2.0 0.5 10 Sep. 21:19-21:56 8876.401 3.524 0.6

7 Sep. 21:18-22:00 8873.402 4.9 0.5 10 Sep. 22:19-23:00 8876.444 3.718 1.1

7 Sep. 22:18-22:59 8873.443 1.8 0.5 10 Sep. 23:31-23:59 8876.490 4.797 1.0

7 Sep. 23:23-23:59 8873.487 3.4 0.7

8 Sep. 00:20-00:58 8873.527 5.1 0.6 11 Sep. 19:18-20:00 8877.319 3.036 0.5

8 Sep. 01:20-02:00 8873.569 3.8 0.5 11 Sep. 20:18-21:00 8877.360 2.176 0.4

8 Sep. 02:20-03:00 8873.611 5.7 0.6 11 Sep. 21:20-22:00 8877.403 0.903 0.4

11 Sep. 22:25-22:59 8877.446 1.1 0.6

8 Sep. 17:11-18:00 8874.233 1.4 0.4 11 Sep. 23:21-23:59 8877.486 3.851 0.8

8 Sep. 18:18-19:00 8874.277 2.3 0.4

8 Sep. 19:18-20:00 8874.319 1.6 0.4 12 Sep. 19:18-20:00 8878.319 3.331 0.5

8 Sep. 20:18-21:00 8874.360 2.1 0.5 12 Sep. 20:18-21:00 8878.360 2.120 0.4

8 Sep. 21:22-21:38 8874.396 1.0 0.7 12 Sep. 21:19-22:00 8878.403 0.248 0.5

8 Sep. 22:19-22:59 8874.444 2.4 0.5 12 Sep. 22:19-23:00 8878.446 0.437 0.7

8 Sep. 23:19-23:58 8874.485 5.2 0.8 12 Sep. 23:19-23:58 8878.486 1.739 0.8

9 Sep. 00:19-01:00 8874.527 5.9 0.6

9 Sep. 01:20-01:59 8874.569 3.0 0.5 13 Sep. 19:18-20:00 8879.319 11.159 0.9

9 Sep. 02:20-03:00 8874.611 4.9 0.6 13 Sep. 20:19-21:00 8879.361 12.901 1.0

9 Sep. 03:19-04:00 8874.652 4.7 0.5 13 Sep. 21:20-22:00 8879.403 14.976 1.1

9 Sep. 04:19-05:00 8874.694 3.4 0.5 13 Sep. 22:19-23:00 8879.444 9.523 0.9

13 Sep. 23:19-23:59 8879.485 9.1 0.9

9 Sep. 18:38-18:59 8875.280 1.4 0.7

9 Sep. 19:18-20:00 8875.319 0.2 0.4 14 Sep. 19:24-19:59 8880.320 5.181 0.6

9 Sep. 20:18-21:00 8875.360 1.4 0.5 14 Sep. 20:19-21:00 8880.361 2.769 0.5

9 Sep. 21:20-22:00 8875.403 0.3 0.5 14 Sep. 21:18-22:00 8880.402 5.245 0.6

9 Sep. 22:20-23:00 8875.444 1.0 0.5 14 Sep. 22:18-22:59 8880.443 2.169 0.7

9 Sep. 23:29-23:56 8875.488 3.7 1.1 14 Sep. 23:22-23:59 8880.486 1.923 0.6

10 Sep. 00:19-00:59 8875.527 3.1 0.6

10 Sep. 01:20-02:00 8875.569 2.5 0.6 15 Sep. 19:20-19:58 8881.319 1.992 0.6

10 Sep. 02:20-03:00 8875.611 2.8 0.5 15 Sep. 20:24-21:00 8881.363 0.990 0.9

10 Sep. 03:19-04:00 8875.652 2.2 0.4 15 Sep. 21:19-22:00 8881.402 0.607 0.7

10 Sep. 04:19-05:00 8875.694 1.1 0.4 15 Sep. 22:20-22:57 8881.443 2.485 0.9

15 Sep. 23:20-24:00 8881.486 0.7 0.6

Table 7: Log of the BBI 5GHz monitoring of IIPeg obtained between 7-15 September 1992. Phases have been calculated according to the ephemeris of Vogt (1981)