Re: Toronto -Day 1

[Annie Robin <annie@obs-besancon.fr>]

Dear all,

Thanks for your work on sunday ! Here are my remarks about it.

Table summary :

WL survey : You mentionned previously : 6 hr would be : 1 hr per filter + 
2*1/2 hr for reobserving (proper motions). Now you have double the
exposure in z. So you must add 1 over 6 in time. This gives 224 nights.

Deep survey : I do not remember the object of this u' survey... Is it just
to add more u photons to the SNe ? Why u' and not z' ? I saw in the
previous messages that the complements would be in u'g'r'... I have missed
something.

Ecliptic survey :

- Do you plan to do the same 1000 sq deg each year or to do a 5000 sq deg 
survey over 5 years ? Not clear in the table.

- Filter : I do not think that g is the good second filter. 
For normal populations this does not matter too much because both colour 
g-r and r-z are good temperature indicators. But for extreme objects, this
matters. Two extreme kind of stars are interesting : the brown dwarfs and
the white. The brown 
are obviouly better seen in z than in g. For white dwarfs it is not true
for the bright part of the sequence. But for the coolest, from Chabrier et
al models, the r-z operates a turn-over so that after cooling to the red,
white dwarfs cool to the blue at about r-z=0.6 corresponding to an age of 10-12
Gyr. On the contrary, g-r would keep red at a constant value of about 1 so that 
there is no way to estimate the age.

The problem would be the sentitivity in z. If we double the exposure in z,
it will take 20% time more to the ES. If you mind this problem, go to the
i filter in place of z.

Field location :

10:00,0=> l=240,b=40 It is Ok for galactic structure.


Data release : 

I am a bit concerned with the release after 3 years. I mean that
proper motions studies will not be possible before these 3 years. But some 
people having access to other survey telescopes could manage to make the

proper motions before us using our first epoch (I think of VISTA and VST) 
(they are in the
south so this remark is valuable for equatorial fields only). I do not
know about survey telescopes in the north (apart from sdss).

I am in my office this afternoon till 17:30 (Paris time) my phone number 
is below. Have a nice and productive day !

Cheers

Annie

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Annie Robin                      Tel: (33)(0)381666941
Observatoire de Besancon         Fax: (33)(0)381666944
BP 1615                          e-mail : robin@obs-besancon.fr
F-25010 Besancon cedex
France
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