[vsnet-chat 7251] Re: [vsnet-obs 53846] Re: data format correction

[arne]

Berto, the Sony HAD chips as used in the Starlight Xpress cameras,
for example, have a definite wide V-band response;
see my M67 Experiment paper.  MDJ's observations were made with an Ap-7
which is a back illuminated CCD with response between V and Rc.  However,
there are bigger problems here.  You should never look at red stars
unfiltered and expect to come close to anyone; the rapidly rising red
continuum and molecular features make wide-band transformation impossible.
Likewise, as mentioned, use of USNO-A (or any astrometric catalog,
including UCAC) for photometry is highly discouraged; the photometry
is basically a placeholder so that field recognition can be accomplished.
There are known decent sequences for most of the stars that MDJ is observing.
The solution is for one of you to work with Daniel José and guide him
towards proper techniques and not just complain on this list.
Arne

Berto Monard wrote:
> I am always puzzled why CV is used for unfiltered CCD photometry with the effective wavelength of an unfiltered CCD chip being close to that of the R..Rc band (for non-red sources). 
> 
> It's like making R estimates from visual observations, not?
> 
> 
> Re: 0003-39  V SCL  2453679.549 CV>16.04 MDJ    V= 10.9 (= about 10.0Rc)
> considering the instrumentation that was used, this red star must have made quite a mark on the image for exposures exceeding a couple of seconds... 
> 
> 
> BTW I am still utilising UCAC2 for making Rc sequences using the empirical formula
> Rc = UCAC - 0.3 (J-K), 
> while also
> V= UCAC + 0.7 (J-K)     /       assuming J-K = V-R, which holds reasonably (+/- 0.2)
> 
> OK, these are not very accurate for magnitudes over 14, but compare them anytime vs calibrated sequences. Derived V mags can also be checked vs ASAS data of constant stars. Such a V sequence interchecked on an image will lead to a set of quite accurate comparison stars for differential photometry.
>     
> I made 1500+ sequences that way...
> 
> Regards,
> 
> Berto Monard
> Bronberg Observatory / CBA Pretoria
> 
> 
> 
>>>>"Sebastian Otero" <varsao at fullzero.com.ar> 09/11/2005 02:17:38 >>>
> 
> ----- Original Message ----- 
> From: "Taichi Kato" <tkato at kusastro.kyoto-u.ac.jp>
> To: <vsnet-obs at ooruri.kusastro.kyoto-u.ac.jp>; <vsnet-obs at yahoogroups.com>
> Sent: Tuesday, November 08, 2005 9:05 PM
> Subject: [vsnet-obs 53844] data format correction
> 
> 
> 
>># CV, CR etc. are for unfiltered CCD photometry
> 
> 
> Those observations were actually unfiltered according to the original 
> report:
> 
> "Mendicini, Daniel José
> Santa Fé, Argentina
> C 14-F/7  AP - 7 CCD
> photometry diferential-unfiltered
> Soft IRIS. Catalogo USNO A2.0"
> 
> BUT the problem here is that the identifications are wrong for most of the 
> stars and the results are not even close to the V mag. from ASAS in any 
> case:
> 
> Mendicini data ---------------------------------- ASAS-3 V
> 
> 1744-06 RS OPH  2453679.535 CV 10.17 MDJ  V= 10.7
> 1744-06 RS OPH  2453679.535 CB 10.92 MDJ
> 1744-06 RS OPH  2453679.535 CR 10.12 MDJ
> 1811-46 RS TEL  2453679.519 CV 10.41 MDJ   V= 9.80
> 1811-46 RS TEL  2453679.519 CR  9.96 MDJ
> 1811-46 RS TEL  2453679.519 CB 11.16 MDJ
> 0106-30  U SCL  2453679.561 CV>16.63 MDJ    V= 15.0
> 0003-39  V SCL  2453679.549 CV>16.04 MDJ    V= 10.9
> 0044-35  X SCL  2453679.552 CV>15.11 MDJ    V= 11.67
> 2106-09 VY AQR  2453679.540 CV>15.82 MDJ   V= 13.8
> 
> I also wouldn't use USNO as a source of photometric values having PEP, ASAS 
> and everything we already know of. Asking for advice or checking what we are 
> doing before flooding the databases with wrong data is always recommended...
> 
> Cheers,
> Sebastian. 
> 
> 
> 
>