Proposal #135

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.

https://ui.adsabs.harvard.edu/abs/2019hst..prop15879R/abstract

Tom Calderwood