Short and Medium term Variability study of
NGC2516 late type stars with
EPIC-XMM
I. Pillitteri 1, G. Micela 2, A. Marino1 , S. Sciortino 2
1: Dip. Scienze Fisiche e Astronomiche, Universita` di Palermo
2: INAF - Osservatorio Astronomico di Palermo
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Outline:
NGC 2516 characteristics and XMM observations.
Short term Variability
Medium term Variability
Summary and Future Work.
EPIC Meeting, Palermo
14-16 Ottobre 2003
NGC 2516 cluster
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Rich Open Cluster, distance 387 pc
Age: ~140 Myr, slightly older than Pleiades
Solar Metallicity (Terndrup et al. 2002)
Optical catalog: Jeffries et al. (2001)
EPIC Meeting, Palermo
14-16 Ottobre 2003
EPIC-XMM observations
• 5 EPIC Calibration Observations, typical obs time: 20 ksec.
• Time coverage: 19 months
Rev.
number
RA
(J2000)
Dec
(J2000)
Obs Time
(ksec)
Filter
M1
M2
PN
Time after
1st obs
(months)
0060
2 segm.
7:58:20
“
-60:52:13
“
20
17
THICK
THICK
Y
Y
Y
Y
Y
Y
0
0092
7:58:22.3
-60:45:36
27
THICK
Y
Y
Y
2
0164
7:58:20
-60:52:13
22
MEDIUM
Y
Y
N
7
0209
2 segm.
7:58:22.3
“
-60:45:36
“
21.4
13.5
THICK
THICK
Y
Y
Y
Y
Y
Y
10
0346
7:58:22.3
-60:45:36
21.2
THICK
Y
Y
Y
19
EPIC Meeting, Palermo
14-16 Ottobre 2003
Previous pubblications based on EPIC data:
•Sciortino et al. 2001:
Analysis of rev. number 0060.
•Ramsay et al. 2003:
Study of variability of 4 sources.
EPIC Meeting, Palermo
14-16 Ottobre 2003
Analysis steps:
1.
2.
3.
4.
5.
Calibrated event files obtained with SAS5.3.3.
Filtering: Energy band : 0.3-5.5 keV, “low” rate time intervals.
Source detection with Wavelet Convolution based code (PWXDetect) on
(MOS1 + MOS2 + PN) of each observation and cross-id. with optical
catalog, selection of a sample of dG and dM type stars.
Light curves and Kolmogorov-Smirnov test for short term variability.
Lx Amplitude Variation distributions for medium term variability.
SAS product ...
EPIC Meeting, Palermo
14-16 Ottobre 2003
Filtering ...
...and Detection
Criteria for selection of the sample
1.
2.
3.
Color index
isolated sources
detected at least once in XMM observations.
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11 dG type stars (B-V0  0.5 & V-I0  0.93)
11 dM type stars (2.2  V-I0  5.0)
EPIC Meeting, Palermo
14-16 Ottobre 2003
Results I. Short term variability
G sample: 11 stars observed 7 times.
• Number of detections: 75/77 ~ 97.4%
• K-S test constant source null hypothesis P0 < 1%:
Variables: 10/75 ~ 13 %
M sample: 11 stars observed 7 times.
• Number of detections: 31/77 ~ 40%
• Variables (K-S test P0 < 1%): 8/31 ~ 26 %
Results similar to field dG and dM stars (Marino et al.
2000, 2002). Different from Pleiades case where dG and
dM stars show similar variability properties.
EPIC Meeting, Palermo
14-16 Ottobre 2003
Light curves.
G type
stars
EPIC Meeting, Palermo
14-16 Ottobre 2003
M type
stars
X-ray spectral variability of a dG star
between two observations.
Star id. JTH 9465 from Jeffries et al.(2001) catalog: B-V 0.82.
Red: obs nr. rev 60-A: quiescent, black: obs nr. rev. 346: flare
“Bump” at ~1.8
keV in the flare
spectrum
EPIC Meeting, Palermo
14-16 Ottobre 2003
Results II. Medium term variability in dG stars
Analysis Amplitude variation of log LX (ALX) of dG stars at ~10
and ~20 month time scales.
•Cumulative Distributions of ALX of NGC2516 dG stars, compared
with analogous Sun, Pleiades (Micela & Marino 2003, Marino et
al. 2003 ) and Hyades (Marino, priv. comm.) distributions.
 Sun data from YOHKOH/SXT full disk images in 0.7-2.5 keV.
 Pleiades and Hyades data from ROSAT observations.
EPIC Meeting, Palermo
14-16 Ottobre 2003
EPIC Meeting, Palermo
14-16 Ottobre 2003
Summary:
1. Short time scales: dG in NGC 2516 are less variables
than dM, similar result in field stars but different from
Pleiades case.
2. Medium time scales: no evidence of solar-like cycle in
NGC 2516 at 10 and 20 month time scales.
Future work:
•Long term (~ yr) variability (XMM<>ROSAT data)
•Analysis of all summed exposures to achieve the
deepest X-ray sensitivity.
EPIC Meeting, Palermo
14-16 Ottobre 2003