THE PROBLEMS OF
SKY SUBTRACTION
AND OF ANOMALOUS MEMBERS
IN YOUNG CLUSTERS:
THE CASE OF NGC 6611
Rosaria (Sara) Bonito
Dipartimento di Fisica e Chimica
Universita' degli Studi di Palermo
INAF-Osservatorio Astronomico di Palermo
NGC 6611 & GES

FLAMES observations (HR15N setup)
(Bonito et al. 2013)

NGC 6611: forthcoming observations
GES
SKY SUBTRACTION & Ha

Nebular contribution to Ha emission
Strongly varying in space and time
 Narrower than stellar


FWZI method
(as EW and Ha10% cannot be derived)
FWZI METHOD (1)

Zoom +/- 3 A around Ha in sky spectra
FWZI METHOD (2)

Normalize: spectrum without the emission line
FWZI METHOD (3)

Difference or ratio original
spectrum/spectrum without the emission line
FWZI METHOD (4)

FWZI(Ha) sky < 3 A
FWZI(Halpha) & ACCRETION

FWZI(Ha) star >> FWZI(Ha) sky
(Bonito et al. 2013)
SKY SUBTRACTION AND Li (1)
Upper limit for EW(Li) using other features
in the Li spectral region (Randich et al. 2009)
 Median sky subtraction (Jeffries & Oliveira 2005)

SKY SUBTRACTION AND Li (1)
Spurious absorption lines due to [SII] 6717 A

SKY SUBTRACTION AND Li (2)
No Li
 No veiling

Age
 Membership

IMPLICATION FOR GES

NGC 6611: forthcoming observations

g Vel

NGC 2264

NGC 6530
BWE STARS IN NGC 6611
(Bonito et al. 2013)
+: members from the Guarcello
et al. (2010) catalog
: all the targets observed with
FLAMES
: BWE stars (with disk)
BWE STARS: WHY?

> 50 %: members
(Bonito et al. 2013)

old members?
 completeness
(De Marchi, Panagia, Guarcello, Bonito et al. 2013)

also in other clusters
 age spread?
 GES
CONCLUSIONS


Sky subtraction
 FWZI(Ha) method
 Spurious absorption lines (Li)
Blue with excesses (BWE) stars
 completeness
 age spread
 other clusters (GES)