Delta-Scuti Observations--How Much Difference Does Choice of Filter Make?

Affiliation
American Association of Variable Star Observers (AAVSO)
Mon, 09/15/2014 - 06:37

I have been logging time-series data for V575 Lyr, a delta-Scuti star,  with V and B filters. I have noticed some  differences between my extracted frequencies (using Peranso and Period04) and some published results. The published results seem to have been taken with  clear filters. How much difference can I expect between, say, a V filter and a clear filter? Or does it make any difference? I have about 27 hours of data over 12 nights. I know that I will collect more photons with a clear filter, but apart from that, should the filter matter? I have been using 200-second exposures with a 12.5" scope and my S/N ratios are well above 100 and my data quality seems to be pretty good. A second frequency of 8.96848 c/d was reported by Van Cauteren & Wils but the closest I get is 9.17125 c/d. Could the second frequency have changed that much over time, or is this because I used a different filter, or what?

Ken

Affiliation
Vereniging Voor Sterrenkunde, Werkgroep Veranderlijke Sterren (Belgium) (VVS)
No influence on period

Hi Ken,

The times of maximum of a pulsating star depend on the filter used for the observations, but there is no influence at all on the periods.
It is unlikely that the second frequency will have changed by as much as you quote, but it is sometimes difficult to determine accurately when the total timespan of the observations is short.  Prewhitening with a slightly different primary frequency may then result in a fairly large difference in the derived secondary frequencies.  Of course this goes for the published observations as well.

Patrick