Affiliation
American Association of Variable Star Observers (AAVSO)
Mon, 11/09/2015 - 16:24

Hi,

Last night did some V-band and I-band photometry on KIC 8462852.  In pulling the sequence for this star, I noticed that the column for I-band has a  Cousins subscript but there is a footnote (29) that indicates APASS which is Sloan I (SI).  As chance would have it I did indeed use a SI filter.  It would seem to make sense to simply report this as SI and forget the fact the sequence column heading shows Cousins I.  Can someone confirm this?

 

Thanks in advance,

John Ott

Affiliation
American Association of Variable Star Observers (AAVSO)
Sloan SI Magnitude versus Ic

John:

IMO, the answer is no. Yes, you have used a Sloan SI filter so you want to report the magnitude as SI not Ic. However, if you use the sequence Ic magnitudes for your comps, you are mixing apples and oranges. Actually not that bad but more like Macintosh and Cortland apples. You need the Sloan SI magnitudes for the comps. They are not the same as the calculated and reported Ic magnitudes (close but not the same). 

The sequence team can confirm that only the Ic magnitude (not SI) is currently reported for the comps in sequences. The Rc and Ic magnitudes given in the sequence are calculated from the Sloan magnitudes measured by APASS. The SI magnitudes for the comps can be found in seqplot (?), or UCAC4 in Vizier if you have the ID?

Sebastian, can you confirm my observation?

Ken

Affiliation
American Association of Variable Star Observers (AAVSO)
i vs Ic

1)  APASS Rc & Ic data is converted from the APASS Sloan data; obviously as Ken points out the Ic values and the i values are not the same.

2)  The Sloan data is not available from SeqPlot as only the Rc & Ic converted values are and this is what you willl see in any APASS sequence.

3)  The easiest way for the observer to capture the Sloan filter data (and by the way, Sloan filter data typically usess lower case letters, i.e. i or r, etc) is to use the coordiantes for the same sequence star that they are using for the V values (and theby having a reportable AUID) into the APASS data base search, which will then display both the B & V values as well as  the Sloan fitler values: 

https://www.aavso.org/download-apass-data

This way the observer will have the sloan i values and will report the result as being that filter.

Per Ardua Ad Astra,

Tim Crawford, CTX, Sequence Team

 

 

 

 

Affiliation
American Association of Variable Star Observers (AAVSO)
Tim,
I'm now recalling a

Tim,

I'm now recalling a conversation from August, I think Arne really answered the question in the following way:

“I think the way I'd handle your Ic vs i' problem right now is to rename your i' filter "I" in your image files, and use the standard TG/TA transforming tools. i' is close enough to Ic that normal transformation will handle it just fine, and untransformed data using Ic comparison stars should also work.

Perhaps put a note in the comments field that you are using the Sloan i' filter, but otherwise proceed like you were doing normal Johnson/Cousins photometry. I don't think you need to purchase a new Ic filter. Then, next year you can submit new data either as Sloan transformed into Cousins, or Sloan native, as you prefer.”

 

--John