White Dwarf Distance Estimate to M5
The A-Team: Andy Layden (PI, BGSU), Adrienne Cool
(SFSU), Ted von Hippel (Gemini Observatories, Hilo), and Ata
Sarajedini (U. of Florida).
Data Reduction:
- Ata's stacked images in WF2, WF3 and WF4 (and Allframe
star-subtraced image of WF2) are available at
ftp.astro.wesleyan.edu (anonymous/email)
[25 Apr 01].
- Ted's matched Allframe/SExtractor data for WF2
(objects found in >= 5V+5I frames; 1st 7 cols from allframe,
remaining from SExtractor) [25 Apr
01].
Timeline (as of 2000 Oct):
Developed after first team meeting, 2000 Oct 14 at Wesleyan. Items
in red are
external deadlines.
2000 Oct 31:
- TvH delivers preliminary Source Extractor results, has
parameters for star/galaxy/blemish discrimination pretty much
finalized. TvH delivers starlist to AS for use in final ALLFRAME
reductions, and to AC for comparison with her visual
discrimination. (See Note#1).
2000 Nov 30:
- AC and AS deliver final instrumental photometry from
respective reduction paths, begin comparisons (joint discussions)
to determine systematic differences. Is one method
preferable?
- TvH (and AL) deliver prescription for CTE and Long-Short
corrections. Program ready to accept final photometric data when
it becomes available. (See Note#2).
- AL delivers preliminary results on comparison between HST and
ground-based photometry. Is Ata/Taft's ground-based M5 data needed
to establish definitive zeropoint? (See Note#3).
2000 Dec 10 (date flexible):
- Teleconference to discuss details so far,
especially choice of final photometry.
2000 Dec 31:
- AC and AS deliver final photometry list(s).
- TvH takes final photom and begins applying CTE and L-S
corrections. Deliver to AL ASAP.
- AL gives assessment of literature reddening values. Do we need
to improve them (via Ata/Taft's CMD and Simultaneous Reddening and
Metallicity Method, and/or via colors of RR Lyrae)?
2001 Jan 15:
- AL delivers comparison between CTE/LS-corrected photom and
ground-based photom. Any systematics? Do we correct the HST photom
(eg, aperture or linearity corrections)? After appropriate
discussion, photometry data set is finalized.
- TvH disseminates his collection of white dwarf models (TvH and
AC may want to discuss appropriate choices/ranges of ages/masses
before).
- Any and all begin playing with distance techniques -- fitting
WDs to models, fitting WDs to observed field WDs with trig-pi's,
fitting WDs to WD sequences in other globulars. (See Note#4).
2001 Jan 31:
- AL delivers mean V(RR), B(RR), I(RR) and K(RR) values derived
from various variable star surveys (transformed when necessary to
the ground-based photometric scale adopted Nov 30).
2001 Apr 10:
- Target for preliminary distance work. Time for collective
discussion -- possible teleconference or team meeting (at
SFSU?).
2001 May 15:
- AL begins writing in
earnest.
- Team approaches consensus on distance
results.
2001 Jun 3-7:
- Present poster at AAS meeting in Pasadena, CA. Team
meeting by any members present.
2001 July 26-31:
- AL presents talk (near-final results?) at IAU
Colloquium on variable stars in Leuven, Belgium?
2001 Aug 15:
Notes:
Note#1:
- AS will provide TvH with montage2 combined image of all long
frames.
- AS will try AC's nonstandard ALLSTAR fitting parameters.
- AC will try Stetson PSFs in place of homegrown PSFs.
Note#2:
- TvH will update his C code with latest coefficients and
distribute.
- TvH will run quick tests on prelim photom to determine
difference between CTE/L-S corrections of Whitmore et al (1999)
and Stetson (1998).
- AL may help with developing relations between PSF-mags and
2"-aperture counts for isolated stars, enabling pipeline
correction of PSF-mags.
- TvH may ponder whether corrections for 34th-row effect may be
warranted.
- TvH will look at V,I contamination corrections -- is it
preferable to derive our own correction or use the standard
prescription for time-dependent "gunking up" of the dewar
window.
- AL may use AS's (or AC's) preliminary 5sec/60s/long photometry
to verify standard L-S corrections (eg, plot V(5s)-V(60s) against
V(60s) and look for trends).
Note#3: There are at least 3 independent
photometry sets in the literature, and there are significant
systematic differences between some of them. Is it possible, through
inter-comparison, to find a preferred photometric zeropoint? If so,
correct Sandquist photometry (only one which covers our field) to
this system and do star-by-star comparison with HST data. If not,
consider having Ata reduce his ground-based M5 photometry (high
quality standards) to serve as a "tiebreaker".
Note#4: If people think it is worthwhile,
AL can extract the archive images of the WDs observed by HST for the
Renzini 1997 paper (Bragagglia on observations?). This allows us to
re-reduce the images using our techniques (AC and/or AS photometry
methods, CTE/L-S corrections, contamination corrections, etc) for
more precise fitting than simply assuming Renzini 1997 values.
Additional observations we may propose if current reductions prove
sub-optimal:
- Obtain ground-based V,I photometry of field WDs. Especially
WDs with large space velocities, indicative of halo a/o thick disk
membership -- old ages and low masses appropriate to comparison
with globular cluster WDs. Well-determined trig parallax also a
must. Search for candidates from McCook and Scion catalog. Use
KPNO 0.9-m, CTIO YALO 1.0-m, and/or snatch few moments from other
observing projects.
- HST-based observations of same?
- Obtain another round of HST images (with WFPC2 or ACS?) to
improve depth of VI CMD and definition of WD sequence in M5.
- WIYN observations of our WFPC2 field to get high-quality
(sub-arcsecond) photom for calibr.
Secondary papers to be derived from HST GO-8310 observations:
- Variable stars in WFPC2 data (especially blue stragglers and
main sequence binaries).
- Variable stars in STIS data (faint main sequence binaries and
pulsating WDs).
- WFPC2 data for frequency of low-mass main sequence
binaries.
- WFPC2 data for ultra-deep main sequence CMD and search for
mass turnover.
- STIS data for same (requires modeling of star/galaxy LFs since
data from only one filter).
- Assorted White Dwarf studies.
Link to page with original list of
tasks.
Updated 2000 Oct 18 -- ACL