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Getting Precise Stellar Parameters in PLATO’s first field. PLATO science conference 24/25 th Feb 2011. T. Granzer, K.G. Strassmeier, & M. Weber. A dedicated input catalog?. Dedicated photometric characterization survey in Strömgren uvby n w and H - PowerPoint PPT Presentation
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Getting Precise Stellar Parameters in PLATO’s first field
PLATO science conference 24/25th Feb 2011
T. Granzer, K.G. Strassmeier,
& M. Weber
• Dedicated photometric characterization survey in Strömgren uvbynw and H
• Deliverables: (b-y), c1, m1, Teff, [M/H], log g; Flux F(H) down to 13mag.
• Constraints: bright limit 9.5, faint 16mag
• First field (fixed) in southern hemisphere
• Challenge: 2000 □2
A dedicated input catalog?
Challenge: 2000 sq-deg
• Super Wasp-South (SAAO), 8x11.1cm lens optics, FoV 7.8x7.8º,~35 pointings, filters ‘on demand’ (?)
• OmegaCam@VST (Paranal): 2.6m Ritchey-Crétien, FoV 1x1º,~2000 pointings, ugriz&H
• RoboTel (C. Armazones): 80cm, Cassegrain, 33.5 arcmin, ~7500 pts., full Strömgren and H set (plus UBVRI, ugriz).
• RoboTel (C. Armazones): 80cm, Cassegrain, 33.5 arcmin, ~7500 pts., full Strömgren and H set (plus UBVRI, ugriz).
Robotel
NGC 891
LBT Mt.Graham5min, seeing 0.8“B-band
RoboTel in Potsdam20min, seeing 3.3“V-band
Identical Instrument
on STELLA-1,1.2m, Izaña
• 40 sec, on 5.8.2010
• 1.3´´ seeing10´´
1´´
Bochum-University/Antofagasta Observatory at base of
Cerro Armazones
~350 clear nights
~50% seeing < 1”
Image: R. Chini
Strömgren indices
(b-y) for eff. Temperaturem1=(v-b)-(b-y) for line blanketingc1=(u-v)-(v-b) for Balmer discontinuity
For late-type (FGKM) stars (dwarfs), m1 is a good proxy for metallicity, c1 for log(g)
Holmberg et al., A&A 475, 519Ramirez & Melendez, ApJ 626, 446Árnadóttir et al., A&A 521, A40
The calibrations used for error analysis are from:
3-year survey?•1300h/year h>30•85% clear nights•Moon: 3-5 days around full moon•Downtime <20% (STELLA)•Standards? (~20min/night)
h13902170
36517552535
72.0*83.0*75.085.0*90.0*85.0
*3*1300
11-17min/pointing
Photometric precisionIncluding slewing/read-out overhead, effective exposure times in y are
•10.3-23.7 sec. (8 filters)•20.1-40.7 sec. (6 filters)•52.6-97.2 sec. (4 filters)
STELLA-1 (1.2m)!
translates to 13.3-15.8
ybv = 3.5-15 mmag,u = 8-30 mmag
…but only in the standard system
Transformation to account for different filter curves (i, i) and atmospheric conditions (k’i, i)
std
mmstdinsmstd
bybyinsbystd
cXkybmm
Xkybyb
,1
1,1,1 ')(')()(
…determined by observation of standard fields, with errors k, , , . nightly
varies slowly
Observe at high and low X
0.030.0150.009
0.0240.0120.007
0.220.05-
0.120.080.015
k’
c1m1(b-y)On STELLA-1, two observations in one night, each 20min at X=1.5 and X=1.05
…errors hold only for the standard field!
Reddening?
Stromgren indices only in de-reddened form, but Plato field at moderate galactic latitude...
Use ß–index, independent of reddening (same ).According to Crawford (AJ 80, 955)
)1,1(7.211.1222.0)()( 2 cmOybybE std
…again one notch on your error budget
Results
Error budget dominated by filter transformations (, ) because only two fields measured. Alleviated by slow variation in these coefficients. Redding only significant in (b-y)
Teff (b-y)
,=0,inst=10mmag
std=11.7mmag
red=18.8mmag
Sample data from Olsen, A&AS 57, 443
Metallicity (b-y,m1,c1)
,=0,inst=17.1mmag
std=19.6mmag
red=5.6mmag
Sample data from Olsen, A&AS 57, 443
log(g)
,=0,inst=21.7mmag
std=39.2mmag
red=3.8mmag
Sample data from Olsen, A&AS 57, 443
Conclusions
Extremely ambitious task.Success depends on good filter transformation.Are there enough standards (in the field)?log(g) at best to distinguish dwarfs and giants.Sacrifice filters/fields?