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Alert Notice 581: Monitoring HD 148703 during upcoming eclipses

June 8, 2017:  Dr. Milena Ratajczak (University of Wrocław) has requested AAVSO observers' assistance in monitoring the very bright (V = 4.23) and very unusual eclipsing binary HD 148703 (HR 6143, N Sco) during its infrequent primary and secondary eclipses scheduled for 2017 June 11 and June 14, respectively.

Dr. Ratajczak writes: "[HD 148703] N Sco is a B-type detached eclipsing binary, which turned out to be an exceptionally interesting object to study when we realised its orbital period is ~223 days and time between eclipses is only ~3.5 days. Such configuration makes it an extremely eccentric system, probably the most eccentric from any objects of that class ever studied. B-type detached eclipsing binaries are very useful tools to test massive-stars stellar evolution models. One can achieve that by comparing observations (light curve + radial velocities) with the theory (models), therefore we aim for an observational campaign of that target. Since the object is very bright, it’s difficult to use professional photometric telescopes (big mirrors) due to saturation issues. That is why we kindly invite amateur astronomers to join the campaign. Data taken during times of eclipses (photometry) and time between eclipses (radial velocities from spectroscopy) which occur next week are crucial to cover in order to determine orbital and stellar parameters of system’s components. Data taken over that time will be of very high value for us."

The next primary eclipse time of minimum is on 2017 June 11 (UT 00:41:45), and the secondary on June 14 (UT 09:17:34). Each eclipse lasts about 20 hours. The amplitude of the primary eclipse is ~0.15 magnitude, and the secondary ~0.35 mag.

PEP V and DSLR V photometry is requested. (CCD V is welcome if saturation can be avoided.) Beginning immediately, one to a few snapshots each night are requested to establish an out-of-eclipse baseline for each observer. These snapshots should continue for a few nights after the secondary eclipse has occurred.

Time series photometry is requested beginning 12 hours before each time of minimum and continuing until 12 hours after. Precision to 0.01 mag or better per single observation is needed. Exposures should be as long as possible without saturating; don't make very short exposures simply for the purpose of gathering more data points.

If B or Ic data can also be obtained, they would be useful; B is preferred to Ic. If you are imaging in more than one filter, please make five V observations for each B or Ic.

Visual observations are also welcome.

Spectroscopy would be useful for radial velocities, but Dr. Ratajczak says a resolution of at least a few thousands is needed. If any such spectra can be obtained now through June 20, they would be very helpful.

Coordinates for HD 148703:   RA  16 31 22.93    Dec  -34 42 15.7  (J2000.0)

Charts: Charts with a comparison star sequence for HD 178403 may be created using the AAVSO Variable Star Plotter (VSP).

Three comparison stars have been selected for photometrists to use (3.564=36, 4.154=42, 5.926=59), although the 42 is very red. To create a chart for photometry, there are two options using VSP: 1) Put HD 148703 at the center, use a 450-arcminute field of view, and use a magnitude limit of 10. This chart will be centered on the variable and will show the 42 and 59. OR 2) Put the coordinates of the 59 at the center (RA 16:39:05.24 Dec -37:13:02.3), use a 450-arcminute field of view, and a magnitude limit of 10. This chart will be centered on the 59 and will show the 36 and 42. The variable will be the bright star NW of the 42.

Visual observers who want to participate should use the binocular chart prepared from VSP by S. Otero:
 
https://www.aavso.org/apps/vsp/chart/?chartid=X19090G

This chart has two comp stars chosen (42 and 46; note that this 42 is not the 42 from the photometry sequence). Information on these comp stars is:

16:06:35.54 [241.64808655°]     -36:48:08.2 [-36.80227661°]     42     4.218 (0.010)20     -0.181 (0.018)
16:12:18.20 [243.07583618°]     -27:55:34.9 [-27.92636108°]     46     4.580 (0.007)20     -0.159 (0.011)

Thanks to AAVSO Sequence Team members Tim Crawford for his recommendations on creating these charts and Sebastián Otero for creating the binocular chart!

Submit observations: Please submit observations to the AAVSO International Database using the name HD 148703. Visual observers should be sure to include the chart ID X19090G in their reports.

This campaign is being followed on the AAVSO Campaigns and Observation Reports Forum at https://www.aavso.org/hd-148703-observing-campaign.

This AAVSO Alert Notice was compiled by Elizabeth O. Waagen.

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