Johnson V is almost always your first choice for photometric filters, as the
next star you observe may be a different color and V is very generic. You may
have to expose longer for your current red star, but you do that for deep-sky
images anyway and scientific photometry always takes about the same amount of
on-sky time. If you only want to image very red stars, your best filter is
Cousins Ic, which is a very red filter (redder than Halpha).
On 6/12/13 11:52 AM, David Kennedy wrote:
> Hi everyone,
> thank you for replying to my questions. Most of my data for NSV 10242 is with
> a Ha 12nm astronomik filter, with blue or green filters the star is hardly
> visible. For an extreme red star which photometric filter would be most useful
> for making observations?.
> *From:* Patrick Wils <mailto:patrickwils@...>
> *Sent:* Tuesday, June 11, 2013 6:36 AM
> *To:* firstname.lastname@example.org <mailto:email@example.com>
> *Subject:* Re: [vsx-dis] Suitable filters to use
> Hi David,
> LRGB filters are difficult to transform to the standard photometric system,
> especially for red stars such as this one. It would be better to use e.g.
> Johnson-Cousins filters.
> As this forum has been inactive and most questions are dealt with on one of the
> AAVSO forums <http://www.aavso.org/forum>, I suggest to ask your questions
> there. There are many more experienced photometrists available to give you more
> complete advice.
> From: David Kennedy <mailto:dken%40live.com.au>
> To: mailto:vsx-dis%40yahoogroups.com
> Sent: Sunday, June 9, 2013 3:07 PM
> Subject: [vsx-dis] Suitable filters to use
> Hello everyone,
> Iâ€™m a new member to the group, joining after noticing a possible variable
> star in my CCD images of the nebula NGC6559. Through the VSX website Iâ€™ve
> found out the star is a suspected variable listed as NSV 10242. Iâ€™ve made
> observations of the star on 3 nights over the past 3.5 weeks and using MaxIm DL
> have measured that itâ€™s decreasing in brightness. However, Iâ€™ve been
> collecting data using the filters I use for imaging (LRGB and Ha
> Astronomik filters) and I would like to know if useful photometric data can been
> gained with these or do I need to use different filters instead? Can
> anyone help?
> David Kennedy