[Aavso-photometry] What are transformation coefficients??
trupti ranka
trupti_ranka at yahoo.com
Thu Mar 13 10:34:31 EDT 2008
Dear Jeff,
Thanks a lot for your explanation. I had a completely wrong idea about TCs!!. Now I understand it much better.
Trupti
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Today's Topics:
1. Nova Cygni 2008 Spectrum (Matthew Beaky)
2. What are transformation coefficients?? (trupti ranka)
3. Re: What are transformation coefficients?? (Jeff Hopkins)
4. Re: Transformation coefficients - Aavso-photometry Digest,
Vol 52, Issue 11 (Brad Walter)
5. Exoplanet host stars in VSX and VSP (Brad Walter)
----------------------------------------------------------------------
Message: 1
Date: Wed, 12 Mar 2008 11:08:19 -0500
From: Matthew Beaky
Subject: [Aavso-photometry] Nova Cygni 2008 Spectrum
To: aavso-photometry at mira.aavso.org
Message-ID:
Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed
After the announcement of the discovery of the apparent nova in
Cygnus (AAVSO Alert Notice #98), I waited through two cloudy nights
before finally getting the chance to acquire a spectrum of N Cyg 08.
I was able to get that spectrum yesterday morning, and it clearly
indicates that N Cyg 08 is in fact a nova. Hydrogen-alpha and
hydrogen-beta lines are both in emission, and many emission lines of
singly-ionized iron are also evident (making this an "Fe II" class
nova, by the classification scheme of Williams (1992, A.J. 104,
725)). The full-width-half-maximum of the H-alpha emission line is
790 km/s. The spectra are posted on the web at http://
www2.truman.edu/~beaky/
For those interested in details, I used a 14-inch SCT with a SBIG
Self-Guiding Spectrograph on its low-resolution setting (4 Angstroms/
pixel). The nova was at visual magnitude ~ 9 at the time of
observation, according to AAVSO "Quick Look" data. Both the short-
wavelength and long-wavelength spectra shown on the web site above
are the sums of four 5-minute measurements (20 minutes total
integration time). The data are wavelength calibrated using a
standard HgNe lamp, but not flux calibrated (though I did acquire
spectra of Vega - a spectrophotometric standard star - and plan to do
more post-processing soon). Measurements were made at the Truman
Observatory, near the campus of Truman State University in
Kirksville, MO.
A check of the AAVSO Quick Look database this morning indicated that
the nova brightened by about a magnitude overnight last night.
Definitely an object worth monitoring!
Matt
********
Matthew M. Beaky
Associate Professor of Physics
Truman State University
beaky at truman dot edu
------------------------------
Message: 2
Date: Wed, 12 Mar 2008 10:52:52 -0700 (PDT)
From: trupti ranka
Subject: [Aavso-photometry] What are transformation coefficients??
To: aavso-photometry at mira.aavso.org
Message-ID: <310121.75262.qm at web53605.mail.re2.yahoo.com>
Content-Type: text/plain; charset=iso-8859-1
Hi all,
After all the discussion that is going on this group lately this may seem a very naive question, but what do transformation coeffs signify??. I read something about it in aavso's astronomical photometry manual but didn't really get it.
Is it that: According to size of telescope and type of detector the number of photons collected from a particular star will differ. So for large telescope we will get larger counts and less for smaller telescope. But since people with different instruments, observing the same star should get same results , we transform this absolute count to some standard count. But in differential photometry since we take differece between the count of two stars, why do we need transformation coefficients here?? shouldn't we get same results irrespective of the instrument used (atleast under ideal conditions).
Trupti
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Today's Topics:
1. Re: Transformation Coefficients (Michael Crook)
2. Re: Transformation Coefficients (Steven Orlando)
----------------------------------------------------------------------
Message: 1
Date: Tue, 11 Mar 2008 20:01:29 +0000 (GMT)
From: Michael Crook
Subject: Re: [Aavso-photometry] Transformation Coefficients
To: Tim Crawford , aavso photometry
Message-ID: <496215.87404.qm at web86211.mail.ird.yahoo.com>
Content-Type: text/plain; charset=iso-8859-1
Tim,
I will be observing LPVs and I understand it is
important to transform in these cases due to the
colour differences between the red variables and the
comparisons.
Is there an 'idiots guide' available to transformed
differential photometry? (I mean a REALLY basic
guide?)
Cheers,
Mick
--- Tim Crawford wrote:
> While we still have somewhat of a related thread
> going
> RE this specific topic (Michael Koppelman's last
> post
> on the topic: Differential vs. absolute magnitudes)
> I
> thought I would post some recent values showing the
> difference between not transformed differential
> photometry and transformed differential photometry
> for
> the benifit of those of you who have never ventured
> into this territory.
>
> This was a recent observation of V371 Per in which I
> had zero-pointed the instrumental magnitudes
> (meaning
> that the IM's would equal the sequence value) of the
> main Comp star; because of this particular action it
> makes it easy to look at this particular Spread
> sheet
> and pull off the following magnitude data.
>
> Filter - Not Transformed - Transformed - Difference
>
> V - 10.959 - 11.979 - .020
>
> B - 11.563 - 11.575 - .012
>
> R - 10.611 - 10.619 - .008
>
> I - 10.217 - 10.230 - .013
>
> It is important for you to understand that other
> systems (scope/ccd/conditions) could have
> significantly larger differences or even
> significantly
> smaller differences (while pesumably the actual
> transformed values would have been quite close) on
> this same target, at the same time, using the same
> comp(s) stars, depending on the calculated
> transformation coefficients for that system.
>
> Tim Crawford CTX'
> Arch Cape Observatory
>
> http://homepage.mac.com/windwalker1/ACObserv.htm
>
>
>
> _______________________________________________
>
> Aavso-photometry mailing list
> Aavso-photometry at mira.aavso.org
>
http://www.aavso.org/mailman/listinfo/aavso-photometry
>
__________________________________________________________
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------------------------------
Message: 2
Date: Tue, 11 Mar 2008 20:29:56 -0400
From: Steven Orlando
Subject: Re: [Aavso-photometry] Transformation Coefficients
To: Michael Crook , aavso-photometry at aavso.org
Message-ID: <004801c883d8$3290e3b0$6501a8c0 at YOURB290464667>
Content-Type: text/plain; format=flowed; charset=iso-8859-1;
reply-type=original
Mick,
An excellent software package Canopus:
http://www.minorplanetobserver.com/MPOSoftware/MPOCanopus.htm
Very reasonably priced.
Also, while there look for the link to Brian D. Warner's book on Lightcurve
Photometry and Analysis. There are spreadsheet instructions in that book
----- Original Message -----
From: "Michael Crook"
To: "Tim Crawford" ; "aavso photometry"
Sent: Tuesday, March 11, 2008 4:01 PM
Subject: Re: [Aavso-photometry] Transformation Coefficients
> Tim,
>
> I will be observing LPVs and I understand it is
> important to transform in these cases due to the
> colour differences between the red variables and the
> comparisons.
>
> Is there an 'idiots guide' available to transformed
> differential photometry? (I mean a REALLY basic
> guide?)
>
> Cheers,
>
> Mick
>
>
>
>
>
> --- Tim Crawford wrote:
>
>> While we still have somewhat of a related thread
>> going
>> RE this specific topic (Michael Koppelman's last
>> post
>> on the topic: Differential vs. absolute magnitudes)
>> I
>> thought I would post some recent values showing the
>> difference between not transformed differential
>> photometry and transformed differential photometry
>> for
>> the benifit of those of you who have never ventured
>> into this territory.
>>
>> This was a recent observation of V371 Per in which I
>> had zero-pointed the instrumental magnitudes
>> (meaning
>> that the IM's would equal the sequence value) of the
>> main Comp star; because of this particular action it
>> makes it easy to look at this particular Spread
>> sheet
>> and pull off the following magnitude data.
>>
>> Filter - Not Transformed - Transformed - Difference
>>
>> V - 10.959 - 11.979 - .020
>>
>> B - 11.563 - 11.575 - .012
>>
>> R - 10.611 - 10.619 - .008
>>
>> I - 10.217 - 10.230 - .013
>>
>> It is important for you to understand that other
>> systems (scope/ccd/conditions) could have
>> significantly larger differences or even
>> significantly
>> smaller differences (while pesumably the actual
>> transformed values would have been quite close) on
>> this same target, at the same time, using the same
>> comp(s) stars, depending on the calculated
>> transformation coefficients for that system.
>>
>> Tim Crawford CTX'
>> Arch Cape Observatory
>>
>> http://homepage.mac.com/windwalker1/ACObserv.htm
>>
>>
>>
>> _______________________________________________
>>
>> Aavso-photometry mailing list
>> Aavso-photometry at mira.aavso.org
>>
> http://www.aavso.org/mailman/listinfo/aavso-photometry
>>
>
>
>
> __________________________________________________________
> Sent from Yahoo! Mail.
> The World's Favourite Email http://uk.docs.yahoo.com/nowyoucan.html
> _______________________________________________
>
> Aavso-photometry mailing list
> Aavso-photometry at mira.aavso.org
> http://www.aavso.org/mailman/listinfo/aavso-photometry
------------------------------
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End of Aavso-photometry Digest, Vol 52, Issue 12
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------------------------------
Message: 3
Date: Wed, 12 Mar 2008 11:29:43 -0700
From: Jeff Hopkins
Subject: Re: [Aavso-photometry] What are transformation coefficients??
To: trupti ranka ,
aavso-photometry at mira.aavso.org
Message-ID:
Content-Type: text/plain; charset="us-ascii" ; format="flowed"
Hi Trupti,
If you are the only person in the world doing photometry, you would
not need to worry about the transformation coefficients for your
system. Your system would be the standard.
Since that is not true and many observers would like to have there
data be accurate with respect to others, a standard system was
created. Your filters, telescope and detector will have different
(slightly) characteristics, spectral response, than other systems. To
level the playing field you must calibrate your equipment against a
set of stars that have been measured and deemed standard
stars/magnitudes.
While not simple, doing these measurements and calibrations to
determine your transformation coefficients require no more than basic
algebra.
There are two other factors that must be considered too. A standard
star that doe not vary will produce different magnitudes at different
air masses (distances from the zenith). To account for that nightly
extinction in each band must be determined and used to adjust the
magnitude to one that would be outside the Earth's atmosphere. There
first order and second order extinction, but most people just set the
second order to zero and ignore it. The last point and one that
cancels if you do differential photometry is the system zero
points(in each band). An 8" system with identical filter, detector
and transformation coefficients will produce a very different
magnitude than a 16" telescope for the same star and air mass and
extinction. The zero points adjust for the sensitivity of the system.
Summary:
You get a number representing the brightness of an object.
(e.g., V filter= 300,000 ADU)
You take that number and take the log (base 10) of it and multiply if
by -2.5 to create the raw magnitude.
-2.5 log (300,000)
V Raw magnitude= -13.69
You adjust for the system sensitivity by adding a zero point factor
(e.g., Zv = 19.09)
You adjust for first order extinction
(k'v * X; where k'v is the V band first order extinction coefficient
and X is the air mass).
(e.g., k'v = 0.1821; X= 1.002; k'v * X = 0.18)
You then transform the data to the standard system with your V
transformation coefficient (epsilon)
(e.g., epsilon = -.03)
The extraterrestrial instrumental magnitude (EIM) is then:
V EIM= -2.5 log(ADU Count) + epsilon(B -V) - k'v * X + Zv
The (B - V) is the B- V value for the star from a star catalogue.
(e.g., 0.15)
V EIM= -13.69 + (-0.03 * 0.15) - 0.18 + 19.09
V EIM= -13.69 -0.0045 - 0.18 + 19.09
V EIM= 5.18
This gets more complicated for the UBRI bands, but is similar.
Jeff
At 10:52 -0700 03/12/2008, trupti ranka wrote:
>Hi all,
> After all the discussion that is going on this group lately this
>may seem a very naive question, but what do transformation coeffs
>signify??. I read something about it in aavso's astronomical
>photometry manual but didn't really get it.
> Is it that: According to size of telescope and type of detector
>the number of photons collected from a particular star will differ.
>So for large telescope we will get larger counts and less for
>smaller telescope. But since people with different instruments,
>observing the same star should get same results , we transform this
>absolute count to some standard count. But in differential
>photometry since we take differece between the count of two stars,
>why do we need transformation coefficients here?? shouldn't we get
>same results irrespective of the instrument used (atleast under
>ideal conditions).
>
> Trupti
--
Jeff Hopkins
HPO SOFT
Counting Photons
http://www.hposoft.com/Astro/astro.html
Hopkins Phoenix Observatory
7812 West Clayton Drive
Phoenix, Arizona 85033-2439 U.S.A.
(623)849-5889
(623) 247-1190 (Fax)
www.hposoft.com
------------------------------
Message: 4
Date: Wed, 12 Mar 2008 18:12:28 -0500
From: "Brad Walter"
Subject: Re: [Aavso-photometry] Transformation coefficients -
Aavso-photometry Digest, Vol 52, Issue 11
To:
Message-ID: <476BFC7B0128E911 at n054.sc0.he.tucows.com> (added by
postmaster at bouncemessage.net)
Content-Type: text/plain; charset="us-ascii"
Hey Tim, are you trying to see if we are paying attention? I think you had a
wandering finger entering the untransformed V mag in your e-mail. This
tally's with the scale of the differences I get on the infrequent occasions
when I transform magnitudes. That reminds me, that I haven't calculated new
transformation coefficients since I replaced my filters last year. I guess I
better take some images of M67 while it is in good position.
>
> Message: 2
> Date: Mon, 10 Mar 2008 15:52:18 -0700 (PDT)
> From: Tim Crawford
> Subject: [Aavso-photometry] Transformation Coefficients
> To: aavso photometry
> Message-ID: <200081.33556.qm at web34402.mail.mud.yahoo.com>
> Content-Type: text/plain; charset=iso-8859-1
>
> While we still have somewhat of a related thread going RE
> this specific topic (Michael Koppelman's last post on the
> topic: Differential vs. absolute magnitudes) I thought I
> would post some recent values showing the difference between
> not transformed differential photometry and transformed
> differential photometry for the benifit of those of you who
> have never ventured into this territory.
>
> This was a recent observation of V371 Per in which I had
> zero-pointed the instrumental magnitudes (meaning that the
> IM's would equal the sequence value) of the main Comp star;
> because of this particular action it makes it easy to look at
> this particular Spread sheet and pull off the following
> magnitude data.
>
> Filter - Not Transformed - Transformed - Difference
>
> V - 10.959 - 11.979 - .020
>
> B - 11.563 - 11.575 - .012
>
> R - 10.611 - 10.619 - .008
>
> I - 10.217 - 10.230 - .013
>
> It is important for you to understand that other systems
> (scope/ccd/conditions) could have significantly larger
> differences or even significantly smaller differences (while
> pesumably the actual transformed values would have been quite
> close) on this same target, at the same time, using the same
> comp(s) stars, depending on the calculated transformation
> coefficients for that system.
>
> Tim Crawford CTX'
> Arch Cape Observatory
>
>
------------------------------
Message: 5
Date: Wed, 12 Mar 2008 18:16:22 -0500
From: "Brad Walter"
Subject: [Aavso-photometry] Exoplanet host stars in VSX and VSP
To:
Message-ID: <476BFC8101262647 at n120.sc0.he.tucows.com> (added by
postmaster at bouncemessage.net)
Content-Type: text/plain; charset="us-ascii"
Would it be possible to issue designations for all of the bright exoplanet
host stars listed in AXA and get sequences for comps in VSP? I think there
are a number of AAVSO members taking data on these stars.
> -----Original Message-----
> From: aavso-photometry-bounces at mira.aavso.org
> [mailto:aavso-photometry-bounces at mira.aavso.org] On Behalf Of
> aavso-photometry-request at mira.aavso.org
> Sent: Wednesday, March 12, 2008 11:00 AM
> To: aavso-photometry at mira.aavso.org
> Subject: Aavso-photometry Digest, Vol 52, Issue 12
>
> Send Aavso-photometry mailing list submissions to
> aavso-photometry at mira.aavso.org
>
> To subscribe or unsubscribe via the World Wide Web, visit
> http://www.aavso.org/mailman/listinfo/aavso-photometry
> or, via email, send a message with subject or body 'help' to
> aavso-photometry-request at mira.aavso.org
>
> You can reach the person managing the list at
> aavso-photometry-owner at mira.aavso.org
>
> When replying, please edit your Subject line so it is more
> specific than "Re: Contents of Aavso-photometry digest..."
>
>
> Today's Topics:
>
> 1. Re: Transformation Coefficients (Michael Crook)
> 2. Re: Transformation Coefficients (Steven Orlando)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Tue, 11 Mar 2008 20:01:29 +0000 (GMT)
> From: Michael Crook
> Subject: Re: [Aavso-photometry] Transformation Coefficients
> To: Tim Crawford , aavso photometry
>
> Message-ID: <496215.87404.qm at web86211.mail.ird.yahoo.com>
> Content-Type: text/plain; charset=iso-8859-1
>
> Tim,
>
> I will be observing LPVs and I understand it is important to
> transform in these cases due to the colour differences
> between the red variables and the
> comparisons.
>
> Is there an 'idiots guide' available to transformed
> differential photometry? (I mean a REALLY basic
> guide?)
>
> Cheers,
>
> Mick
>
>
>
>
>
> --- Tim Crawford wrote:
>
> > While we still have somewhat of a related thread going RE this
> > specific topic (Michael Koppelman's last post on the topic:
> > Differential vs. absolute magnitudes) I thought I would post some
> > recent values showing the difference between not transformed
> > differential photometry and transformed differential photometry for
> > the benifit of those of you who have never ventured into this
> > territory.
> >
> > This was a recent observation of V371 Per in which I had
> zero-pointed
> > the instrumental magnitudes (meaning that the IM's would equal the
> > sequence value) of the main Comp star; because of this particular
> > action it makes it easy to look at this particular Spread sheet and
> > pull off the following magnitude data.
> >
> > Filter - Not Transformed - Transformed - Difference
> >
> > V - 10.959 - 11.979 - .020
> >
> > B - 11.563 - 11.575 - .012
> >
> > R - 10.611 - 10.619 - .008
> >
> > I - 10.217 - 10.230 - .013
> >
> > It is important for you to understand that other systems
> > (scope/ccd/conditions) could have significantly larger
> differences or
> > even significantly smaller differences (while pesumably the actual
> > transformed values would have been quite close) on this
> same target,
> > at the same time, using the same
> > comp(s) stars, depending on the calculated transformation
> coefficients
> > for that system.
> >
> > Tim Crawford CTX'
> > Arch Cape Observatory
> >
> > http://homepage.mac.com/windwalker1/ACObserv.htm
> >
> >
> >
> > _______________________________________________
> >
> > Aavso-photometry mailing list
> > Aavso-photometry at mira.aavso.org
> >
> http://www.aavso.org/mailman/listinfo/aavso-photometry
> >
>
>
>
> __________________________________________________________
> Sent from Yahoo! Mail.
> The World's Favourite Email http://uk.docs.yahoo.com/nowyoucan.html
>
>
> ------------------------------
>
> Message: 2
> Date: Tue, 11 Mar 2008 20:29:56 -0400
> From: Steven Orlando
> Subject: Re: [Aavso-photometry] Transformation Coefficients
> To: Michael Crook , aavso-photometry at aavso.org
> Message-ID: <004801c883d8$3290e3b0$6501a8c0 at YOURB290464667>
> Content-Type: text/plain; format=flowed; charset=iso-8859-1;
> reply-type=original
>
> Mick,
>
> An excellent software package Canopus:
>
> http://www.minorplanetobserver.com/MPOSoftware/MPOCanopus.htm
>
> Very reasonably priced.
>
> Also, while there look for the link to Brian D. Warner's book
> on Lightcurve Photometry and Analysis. There are spreadsheet
> instructions in that book
> ----- Original Message -----
> From: "Michael Crook"
> To: "Tim Crawford" ; "aavso photometry"
>
> Sent: Tuesday, March 11, 2008 4:01 PM
> Subject: Re: [Aavso-photometry] Transformation Coefficients
>
>
> > Tim,
> >
> > I will be observing LPVs and I understand it is important
> to transform
> > in these cases due to the colour differences between the
> red variables
> > and the comparisons.
> >
> > Is there an 'idiots guide' available to transformed differential
> > photometry? (I mean a REALLY basic
> > guide?)
> >
> > Cheers,
> >
> > Mick
> >
> >
> >
> >
> >
> > --- Tim Crawford wrote:
> >
> >> While we still have somewhat of a related thread going RE this
> >> specific topic (Michael Koppelman's last post on the topic:
> >> Differential vs. absolute magnitudes) I thought I would post some
> >> recent values showing the difference between not transformed
> >> differential photometry and transformed differential
> photometry for
> >> the benifit of those of you who have never ventured into this
> >> territory.
> >>
> >> This was a recent observation of V371 Per in which I had
> zero-pointed
> >> the instrumental magnitudes (meaning that the IM's would equal the
> >> sequence value) of the main Comp star; because of this particular
> >> action it makes it easy to look at this particular Spread
> sheet and
> >> pull off the following magnitude data.
> >>
> >> Filter - Not Transformed - Transformed - Difference
> >>
> >> V - 10.959 - 11.979 - .020
> >>
> >> B - 11.563 - 11.575 - .012
> >>
> >> R - 10.611 - 10.619 - .008
> >>
> >> I - 10.217 - 10.230 - .013
> >>
> >> It is important for you to understand that other systems
> >> (scope/ccd/conditions) could have significantly larger
> differences or
> >> even significantly smaller differences (while pesumably the actual
> >> transformed values would have been quite close) on this
> same target,
> >> at the same time, using the same
> >> comp(s) stars, depending on the calculated transformation
> >> coefficients for that system.
> >>
> >> Tim Crawford CTX'
> >> Arch Cape Observatory
> >>
> >> http://homepage.mac.com/windwalker1/ACObserv.htm
> >>
> >>
> >>
> >> _______________________________________________
> >>
> >> Aavso-photometry mailing list
> >> Aavso-photometry at mira.aavso.org
> >>
> > http://www.aavso.org/mailman/listinfo/aavso-photometry
> >>
> >
> >
> >
> > __________________________________________________________
> > Sent from Yahoo! Mail.
> > The World's Favourite Email http://uk.docs.yahoo.com/nowyoucan.html
> > _______________________________________________
> >
> > Aavso-photometry mailing list
> > Aavso-photometry at mira.aavso.org
> > http://www.aavso.org/mailman/listinfo/aavso-photometry
>
>
>
> ------------------------------
>
> _______________________________________________
> Aavso-photometry mailing list
> Aavso-photometry at mira.aavso.org
> http://www.aavso.org/mailman/listinfo/aavso-photometry
>
> End of Aavso-photometry Digest, Vol 52, Issue 12
> ************************************************
>
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