EPIC Meeting, Palermo 14-16 Ottobre 2003
Short and Medium term Variability study of NGC2516 late type stars with
EPIC-XMM
Outline:• NGC 2516 characteristics and XMM observations.• Short term Variability• Medium term Variability• Summary and Future Work.
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
EPIC Meeting, Palermo 14-16 Ottobre 2003
NGC 2516 cluster
• 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. Calibrated event files obtained with SAS5.3.3.2. Filtering: Energy band : 0.3-5.5 keV, “low” rate time intervals.3. 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.
4. Light curves and Kolmogorov-Smirnov test for short term variability.5. Lx Amplitude Variation distributions for medium term variability.
SAS product ... Filtering ... ...and Detection
EPIC Meeting, Palermo 14-16 Ottobre 2003
Criteria for selection of the sample
1. Color index
2. isolated sources
3. detected at least once in XMM observations.
• 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.
M type stars
G type stars
EPIC Meeting, Palermo 14-16 Ottobre 2003
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.