Date: Fri, 1 Feb 2008 17:31:38 -0700 (MST) Subject: Re: 2.5m obslog 20080131 (MJD 54497) From: "Daniel Oravetz" Thanks for the clarification/suggestions regarding plate 2912. Last night we had guide stars on gotoField pretty well centered for the cartridge prior to plate 2912 and the cartridge after plate 2912, so it seemed the pointing was good. With your suggestions and a bit of luck with stable seeing, hopefully we can get this plate done. DanO > > I second Connie's comments, and add a couple of notes: > > Plate 2912 is a seguefaint plate which targets the > clusters NGC 2158, M35. SEGUE is very interested > in getting good spectra for this plate. > > It's mate, plate 2887, is already complete -- and > a look at the velocities, shows that it was a success, > we obtain good numbers of targets in the NGC 2158 and M35 fields, > with accurate RVs. > > The guide stars for plate 2912 should be very similar, > and in some cases identical to those for plate 2887, > so we should be able to find them. > > Since this field is so crowded, if the pointing is not > 'perfect' (within a couple arcsec) I think there's some chance > that one could latch onto some nearby field stars as > possible guide stars rather than the true set of guide stars. One > may have to search around a bit, or put on a plate that you > know you can find first (maybe 2887?) and 'sync up' then shift to > this plate with the same sync. > > Also, as Connie said, integrating longer may help a bit. > > Sorry about the design bug... > > Let us know how it goes in upcoming nights. > > thanks, > -brian > > On Fri, 1 Feb 2008, Constance Rockosi wrote: > >> >> This is about plate 2912, the one with faint guide stars. >> >> This plate is at l,b 187,1. I assume it is the latest cluster plate >> (I was shamefully useless for the last round of plate design for >> SEGUE) The problem is that this field has an average extinction E(B-V) >> of 0.9. So the guide stars are faint because we are looking through a >> ton of crud. >> >> A look at the seguets code says that, sure enough, we use de-reddened >> psf magnitudes to select guide stars, certainly a bug. >> >> E(B-V) is about 3.5 magnitudes of extinction if you use the SFD98 value >> for R_g to convert from E(B-V) to A_g. >> >> Plotting the g-band fiber mags vs. dereddened psf mags for the guide >> stars selected for this plate show about that expected offset. >> >> What to do about it? That's about a factor of 25 attenuation. >> Dmitry's and Dan's very helpful log entry (thanks!) says they were >> using 25 sec exposures. We are stuck with this field since we >> want this cluster, and the scatter in the fiber vs. dereddened >> magnitude plot shows a min attenuation of 2 magnitudes for the >> potential guide stars on this plate -- pretty bad over the entire >> 7 square degrees. >> >> If you can try this plate (and it's mate, 2887) with 1-2 minute >> guider exposures it would be worth doing. Hopefully it will help >> now that you know to *expect* faint guide stars on this plate. >> >> Sorry for the confusion. >> >> --Connie >> >> On Fri, Feb 01, 2008 at 05:42:09AM -0700, Dmitry Bizyaev wrote: >>> >>> APACHE POINT OBSERVATORY SDSS 2.5M >>> >>> OBSERVING LOG >>> Thursday January 31, 2008 >>> >>> (MJD 54497) >>> >>> ---=== OBSERVING TEAM ===--- >>> >>> Dan Oravetz >>> Dmitry Bizyaev >>> Shannon Watters (afternoon) >>> >>> >>> ---=== OBSERVING PLAN ===--- >>> >>> Science! >>> >>> >>> >>> ---=== OBSERVING SUMMARY ===--- >>> >>> Added signal to cart. 9 plate 2865 >>> Got a problem finding guide stars for cart.7 plate 2912 (too faint >>> guide >>> stars??) >>> Finished cart. 5 plate 2885 and cart 4 plate 2915 >>> Added signal to cart. 3 2659. >>> Second part of the night was in clouds. They really hurt observations >>> close to >>> the morning. >>> >>> >>> >>> 03:03Z Cartridge 7 plate 2912 mounted. >>> We see just a few guide stars in the field, even with 25 sec guider >>> exposure. >>> Focus loop doesn't help much. Some more guide stars are seen (up to 9) >>> but >>> guider doesn't understand it. Number of g. stars changing from 3 to 8 >>> from >>> exposure to exposure. All other parameters are ok. Seeing is around >>> 2.5, >>> guider shows efficiency 110%. Something is wrong with this cartridge. >>> We >>> decided to mount #4 instead. >>> >> >> DSS DSS DSS DSS DSS Digital Sky Survey DSS DSS DSS DSS DSS DSS >> DSS *** The information posted to SDSS mailing lists is proprietary *** >> DSS This is message 3901 in the sdss-25mlog archive, URL >> DSS http://www.astro.princeton.edu:81/sdss-25mlog/msg.3901.html >> DSS The index is at >> http://www.astro.princeton.edu:81/sdss-25mlog/INDEX.html >> DSS To join/leave the list, go to >> DSS >> http://www.astro.princeton.edu:81/cgi-bin/mailinglists.pl/show_subscription?list=sdss-25mlog >> DSS To post a message, mail it to sdss-25mlog@astro.princeton.edu >> DSS >> DSS DSS DSS DSS DSS DSS DSS DSS DSS DSS DSS DSS DSS DSS DSS DSS >> > > DSS DSS DSS DSS DSS Digital Sky Survey DSS DSS DSS DSS DSS DSS > DSS *** The information posted to SDSS mailing lists is proprietary *** > DSS This is message 3902 in the sdss-25mlog archive, URL > DSS http://www.astro.princeton.edu:81/sdss-25mlog/msg.3902.html > DSS The index is at > http://www.astro.princeton.edu:81/sdss-25mlog/INDEX.html > DSS To join/leave the list, go to > DSS > http://www.astro.princeton.edu:81/cgi-bin/mailinglists.pl/show_subscription?list=sdss-25mlog > DSS To post a message, mail it to sdss-25mlog@astro.princeton.edu > DSS > DSS DSS DSS DSS DSS DSS DSS DSS DSS DSS DSS DSS DSS DSS DSS DSS >