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?