epic meeting, palermo 14-16 ottobre 2003 short and medium term variability study of ngc2516 late...

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


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-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


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.


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


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)


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.


Light curves.

M type stars

G 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


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.


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 short and medium term variability study of ngc2516 late...

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