AAVSO: American Association of Variable Star Observers

Proposal #86

Proposer (17557) Mark Blackford (markgblackford@outlook.com) obscode: BMGA
Assigned To(3663) Dirk Terrell
Date SubmittedSept. 9, 2018

Target Name: V777 Sgr

Type: EA/GS (β Persei-type (Algol) eclipsing binary with one or more giant or supergiant components)

R.A., Dec: 17 46 25.39, -26 12 01.1

Magnitude: 8.59 - 8.67 V, 10.35 – 10.68 in B
From our 2016 measurements eclipse depth was found to be ~0.08 in V and ~0.33 in B.

Background: The long period (~936 d) eclipsing binary V777 Sgr will be undergoing an eclipse from October to December this year. Time of mid eclipse is predicted to be JD 2458426.491 or 3 November, 2018. During the ingress phase, between about 4th to 9th October, V777 Sgr will be well positioned for early evening observations. It will be too low in the sky during the egress phase.

During the last eclipse in 2016 BSM-South and/or BSM-Berry observed the V777 Sgr each clear night for about 250 days starting a few days prior to first contact, through until well beyond fourth contact. These observations, along with those of several Variable Stars South observers allowed an improved estimate of the orbital period. However, for the 2016 eclipse the ingress and egress phases were poorly sampled. Thus we have no useful measurements of the relative diameter of the hot blue component being eclipsed.
We have checked the literature and southern sky survey databases such as ASAS and ASAS-SN but have not found suitable photometry during the ingress or egress phases for any previous eclipse.

Aim: During the upcoming 2018 eclipse we aim to obtain well sampled B and V light curves of the ingress phase including a week or more prior to first contact and a week or more after second contact. This will require observations from as large a spread of longitude as possible. We have observers in New Zealand, eastern Australia and South Africa. The inclusion of BSM-South (Victoria, Australia) and BSM-Berry (Western Australia) would provide valuable additional observations.

We request that BSM-South and BSM-Berry observe V777 Sgr each clear night between September 15th (or as soon as possible) through until October 25th. A set of 5 images in B and 5 images in V should be recorded at the end of astronomical twilight. These should be repeated each hour until V777 Sgr reaches an altitude of 30 degrees.

Initially V exposures of 10 sec and B exposures of 30 sec are requested, but these will be adjusted as necessary to achieve high SNR.

Target RA (H.HH) Dec (D.DD) Magnitude Telescope Observation Frequency Expiration Date Proprietary Term
V777 Sgr 17.773719 -26.20031 8.59–8.69 1 Year


(2911) Michael Nicholas — Sept. 15, 2018, 9:51 p.m.

Arne moved the V777 Sgr plan into a separate project for Mark. It is currently under AAVSO_Monitoring,

(2911) Michael Nicholas — Sept. 25, 2018, 6:11 p.m.

09/25/2018 Request update: Currently there are 3 images in each of the BVRI filters, and only one set is recorded each night.
I would like to have the schedule changed to so that a set contains 5 images in each of B and V, and have two sets of images recorded at each telescope each clear night. The first set as early in the evening as possible (but not in twilight) and the second set when V777 Sgr reaches 40 degrees elevation.
The current exposure times (40sec in V, 80sec in B) are fine.

(2911) Michael Nicholas — Sept. 26, 2018, 5:28 p.m.

REQUESTER=BMGA has requested images sent to BDJB VPhot account

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