ISIS, BeSS standard and observatory coordinates

[Robin Leadbeater]

ISIS includes the observatory name BSS_SITE in the header but not the observatory coordinates BSS_LAT, BSS_LONG and BSS_ELEV

This is ok for spectra generated for BeSS as the observatory names are registered with their coordinates. ISIS and the BeSS standard though are now being used in many other areas of amateur spectroscopy. This gives a problem as spectra reduced to BeSS standard (ie topocentric) cannot be heliocentric corrected without knowing the observatory coordinates.

As the observatory coordinates are already entered in ISIS, I suggest that they are also included as standard in the ISIS fits header using the available BeSS names BSS_LAT, BSS_LONG and BSS_ELEV.

Robin

[Ken Harrison]

Robin,
What about just editing the fits header and adding the necessary data?
In BASS project ( and VSpec?) there's an option to verify to BeSS standard...

[Robin Leadbeater]

Hi Ken,

I would prefer an automated solution rather than having to edit the header every time. The BeSS database automatically adds the coordinates to the header when the spectrum is submitted, based on the coordinates it holds for the particular BSS_SITE but that is no help in the general case.

A workround in ISIS could be to use a different observatory descriptor string which includes the coordinates in BSS_SITE Then at least the observatory coordinates would be included in the header in some form but it would be better to have the coordinates as key words so they can be picked up automatically to do the heliocentric corrections subsequently.

As an example of the problem, most (if not all) of the hundreds of spectra submitted to the Nova Del campaign do not have the observatory coordinates in the header which makes it impossible to heliocentric correct them without knowledge of the observatories.
http://www.astrosurf.com/aras/Aras_Data ... l-2013.htm

Robin

[Francois Cochard]

Robin, and all,

This is an important question.

First, I remind that if we made this choice in BeSS (using a form for observer, site and instrument), this is to ensure the data integrity : all spectra taken from a given observatory always have the same data, with no risk for human error.

But "BeSS standard" (in fact, we should say FITS standard with BeSS keywords) is now used as a reference, even for spectra that are not BeSS related - and this is a very good thing.

In the last update of the BeSS file specification, we added a comment to extend the format to other applications (BeSS file spec is at http://basebe.obspm.fr/basebe/Accueil.php?flag_lang=en) :

The BeSS fits file format contains the minimum list of keywords required to upload spectra
in the BeSS database. However, since spectra can be used for general exchanges
independently from BeSS, at upload BeSS adds some important keywords in the header
of the spectra if they are not present yet, based on the observer, instrument, and site
records. In particular this concerns the following keywords: RA, DEC, EQUINOX or
RADECSYS, TELESCOP, DETNAM, INSTRUME, BSS_LAT, BSS_LONG, BSS_ELEV,
BSS_ESRP or BSS_ITRP, and BSS_SRPW. In this way, fits spectra downloaded from
BeSS are usable by anyone in other context.

Then, for any profile file used outside of BeSS, it is highly recommened that all these keywords are present in the header.
If these data are in the header and file is sent to BeSS, a check will be made automatically to check that data are consistent (if not, a warnng will be sent at the upload).

It means that any reduction software could include from now (hum... for some years :>) all these data when exporting in "BeSS" mode.

Keep in mind that we cannot create a "universal" format, which will fulfill all programs in the world (including future programs) - this is a topic that we already discuss deeply in the past. Each program has (or may have) its own specificity. But as far as we know, all the BeSS keywords can be considered as a "basic set of keyword" for spectroscopy. This is why it is highly recommended to use it, even outside BeSS.

The example you mentionned (missing site coordinates in nova del spectra) is a good demonstration of what is to be required within a program - what I mean is that each program should define which data it requires - and check that BeSS keywords cover this need.

Now, the point is that we've not the power of changing all reduction software... Christian, could you make a small miracle for ISIS ? (;>).

Friendly,

François

[Malcolm Locke]

Also worth noting is that SITELAT, SITELONG and SITEALT are more generic headers used for this purpose.

[Robin Leadbeater]

Hi Francois,

There are several amateur organisations and groups currently thinking about or in the process of setting up spectroscopic databases. As far as I know we are the only group so far to have a developed a standard format and header (BeSS). I think we urgently need now to propose a universal fits header for amateur use, probably based on the extended BeSS but with more universally used keywords in place of the BeSS specific keywords. (It cannot be truly universal of course but it should allow for the most commonly needed information. Is there already anything similar in the professional area?) If we do not do it, someone else will eventually and we might not like the result !

Cheers
Robin

[Ken Harrison]

+1 from me!

The IDAS database will follow Francois' recommendations.

[Paolo Berardi]

Very interesting topic. Also our small italian group is considering the development of a spectroscopic (and photometric) database for generic observations. We will certainly have flexibility to adapt it at a later stage but it would be nice to know as soon as possible the main "standard" keywords.

Thank you for your great support!
Paolo

[Christian Buil]

If I did not put keywords like BESS_LON in ISIS, it is precisely because... BeSS database validation process (as I guess)

Suppose I put in the header (from ISIS for example):

BESS_LON = 1.34239
BESS_SITE = 'Castanet'

and BeSS expect:

BESS_LON = 1.342391

or

BESS_LON = 1.34238

A warning or error is returned during validation process (because BeSS database double verification...), which is not justified in my point of view. The problem is not simple. It is a disturbing issue. To do something, I prefer to use keywords SITELONG, SITELAT, ...

Christian

[Robin Leadbeater]

I suggest we leave the header for input into BeSS as it is today because this will avoid discussions about whether BeSS is working in the best way.

We can then have a universal header for amateur spectra which can be recommended for spectra submitted to any general amateur database. This could be based on the BeSS output header for example but use standard keywords in place of the BSS_ words. The choice of type of header could be a selection in the data reduction software (ISIS BASS VSpec etc)

Robin