AAVSO: American Association of Variable Star Observers

Proposal #135

Proposer (17571) Tom Calderwood (tjc@cantordust.net) obscode: CTOA
Assigned To(3663) Dirk Terrell
Date SubmittedMarch 11, 2020

In my capacity as head of the PEP section, I have received a request from Adam Riess of STScI for ground-based photometry in support of a Hubble project, the abstract for which can be found below. For 20 bright cepheids, he primarily needs H band photometry, for which the PEP group has the technology, but he also needs VI data, which can be most effectively gathered with BSM, especially on account of targets in the far southern sky.

There are two wrinkles in this project. First, the Hubble proposal falls in the "SNAP" category - short pointings that are shoehorned into otherwise unusable Hubble time. Although STScI has approved 20 single-epoch cepheid observations, the targets will be chosen from a list of 40 based upon actual Hubble scheduling. At this time, the identities of only 6 targets are known.

Second, the BSM network is undergoing an upgrade, and we need to be mindful of the hardware and software situation. For instance, we will want to observe individual targets with stable instrumental and data processing configurations. And since the targets are bright, field-of-view becomes a concern for chosing comparison stars.

On the positive side, not a great deal of data are needed. Ideally, a single pulsation would be sampled on the order of 16 times (The cepheids are of the short-period kind, less than 8 days). Weather being what it is, of course, that may not be possible. Adam posits that it would be satisfactory to sample multiple pulsations on the order of 20 times in total. More data would not hurt, of course, and might be necesssary if uncertainties are high. Absolute accuracy is not needed - we require only that the comparison stars be stable. Furthermore, data collection need not be coordinated with the Hubble schedule.

While I give specifications for the first six targets, the BSM team and I would need to work out more details for this program.


Tom Calderwood

Target RA (H.HH) Dec (D.DD) Magnitude Telescope Observation Frequency Expiration Date Proprietary Term
R Mus 12.701397 -69.40756 5.93–6.73 BSM_S Sept. 23, 2020 1 Year
S TrA 16.019644 -63.77653 6.01–6.77 BSM_S Sept. 23, 2020 1 Year
ER Car 11.161428 -58.83772 6.58–7.13 BSM_S Sept. 23, 2020 1 Year
AP Sgr 18.217361 -23.11728 6.52–7.41 BSM_S Sept. 23, 2020 1 Year
RY CMa 7.277122 -11.48731 7.71–8.45 BSM_S Sept. 23, 2020 1 Year
V386 Cyg 21.244564 41.71633 9.25–9.97 BSM_NH2 Sept. 23, 2020 1 Year


(4726) Kenneth Menzies — March 13, 2020, 11:38 a.m.


It would help enormously if you would prepare a small table clarifying what observing frequency you want rather than my trying to interpret what text you have provided above. I understand you want V and I filters BUT how often per night (once, three grabs to stack, other?). Monitor every clear night or every x nights? These will be committed to both BSM_S and BSM_AU for most, except for v386 cyg which will go to BSM_NH2 and BSM NM and BSM Hamren in MA. That helps avoid poor weather on a given night.

And when do you want to END the project?

Ken (kenmenstar@gmail.com)

(3663) Dirk Terrell — March 16, 2020, 12:06 p.m.

The TAC suggests gathering data in BVRI and Stella suggests communication with the LPV section to see if any of them might be able to help/.

(17571) Tom Calderwood — March 16, 2020, 10:50 p.m.


My apologies. The target list was not meant to be detailed enough to begin observations, that's why I said "BSM team and I would need to work out more details". I should have been clearer. I am awaiting more details from Adam.

(4726) Kenneth Menzies — March 22, 2020, 4:41 p.m.

Plans committed to appropriate BSM scopes. Adjusted center of field for three targets as requested. Watch images to check FOV and SNR of targets.

(17571) Tom Calderwood — March 27, 2020, 5:41 p.m.

V386 Cyg aimpoint needs adjusting to 12:17:00 41:58:00

Only V and I band are needed. From the 7s test exposures, it appears we need ~700sec in V and 1000sec in I. This would get ~40,000 counts

(4726) Kenneth Menzies — April 29, 2020, 7:27 p.m.

Exposures updated

R Mus V 20s, I 20s

S TrA V 30s, I 20s

ER Car V 40s, I 40s

RY CMa V 60s, I 40s

AP Sgr V 60s, I 40s

Comments on this proposal are closed.