Transcript Pallavicini - IASF Milano

XMM-Newton EPIC Observations of Stellar
Clusters and Star Forming Regions
XMM-Newton observations of open clusters and star forming regions
R. Pallavicini and
and E.E.
Franciosini
R. Pallavicini
Franciosini
INAFOsservatorio
Astronomico
di Palermo,
Italy
Osservatorio
Astronomico
di Palermo,
Italy
S. Randich
S. Randich
Osservatorio Astrofisico di Arcetri, Florence, Italy
Osservatorio Astrofisico di Arcetri, Florence, Italy
EPIC Consortium Meeting, Palermo, 14-16 October 2003
Why observing stellar clusters in X-rays
• Open clusters constitute homogeneous samples of stars with approximately
the same age, distance and chemical composition
• They are fundamental tools to study stellar structure and evolution as well
as the dependence of chromospheric and coronal activity on stellar rotation
and dynamo-generated magnetic fields
• The X-ray emission of late-type stars in clusters is in fact a strong function
of magnetic activity as measured e.g. by the Rossby number (a combination
of rotation and convection zone properties)
• Since late-type stars suffer magnetic braking during their evolutionary
history, coronal activity is a decreasing function of age through the
influence of stellar rotation on the dynamo mechanism
• X-ray sources in star forming regions and in young clusters provide
therefore a powerful tool to identify PMS stars and cluster members
The cluster around sigma Orionis
Equivalent MOS exposure time
for the combined image: 217 ksec,
sensitivity at center > 2.5 x 1028
erg/sec
Cluster discovered by
ROSAT around the
O9.5V star s Ori.
age 2-5 Myr
d = 350 pc
241 X-ray sources detected with
ML>10, 86 identified with cluster
members, including the hot stars
s Ori AB and E, and 7 very-low
mass stars (later than M6)
including the brown-dwarf
candidate S Ori 25 and the
planetary mass object S Ori 68
An X-ray flare from the hot star s Ori E
A similar flare seen with ROSAT
by Groote & Schmitt (2003)
who attributed it to the hot star.
We believe it more likely that the
flare originated from an unseen
late-type companion of the hot
star because of the unusually
high temperature of the quiescent
preflare corona
Flare spectrum: T1= 0.75 keV, T2=3.4 keV, EM2/EM1 = 5
Quiescent spectrum : T1= 0.3 keV, T2=1.3 keV, EM2/EM1= 1
EPIC spectra of sigma Ori stars
s Ori AB
O9.5 V
s Ori E
B2Vp
Source 3
K0+K5
Source 4
K3
Rotationally modulated source in the s Ori cluster
The MOS light curve
of source 4 (Sp. K3)
appears to be rotationally
modulated with a period
of about 9 hours due to
surface activity.
EPIC MOS observation of the T Tauri star SU Aur
The MOS field containing
about 130 X-ray sources
mostly PMS stars
The light curve of the central source
SU Aur (a classical T Tauri star)
showing frequent flaring
The EPIC MOS spectrum of SU Aur
Exp. Time 130 ks
T1= 0.67 keV
EM1= 1.02 E53
T2 = 1.67 keV
EM2 = 2.24 E53
T3 = 4.75 keV
EM3 =1.64 E53
Fe = 0.6 solar
Is Praesepe really different from the Hyades ?
Praesepe is a cluster with about
the same age as the Hyades and
slightly lower metallicity.
On the basis of ROSAT observations
a much lower detection rate of cluster
sources was reported for Praesepe
than for the Hyades (Randich &
Schmitt 1995) suggesting that a cluster
of a given age may not be representative
of all clusters with the same age.
Age 600 Myr, metallicity about solar
Combined exp. time : 279 ks
Sensitivity at center: 5 x 1027 erg/s
(a factor 4 better than ROSAT)
This discrepancy could not be explained
on the basis of different distributions of
rotation rates or as due to contamination
by non-members.
The XLDF of Praesepe and Hyades seen by ROSAT and XMM EPIC
From XMM-Newton data
From ROSAT data
Praesepe might result from the merging of two clusters of different ages
Spectra and variability of Praesepe stars
XMM-Newton vs. ROSAT
EPIC PN spectra of the 3 brightest
sources in the Praesepe field
XMM EPIC observations of the a Persei cluster
XMM-Newton vs. ROSAT
Cluster age about 50 Myr, d=190 pc
275 ks combined exp time, 154 X-ray sources detected with ML > 10:
only 13 cluster members in the XMM field, all but one detected
(sensitivity at field center : 7x1027 erg/s, an order of magnitude higher
than the previous ROSAT observations).
A Hyades field around VB71 (Theta1 Tau)
135 X-ray sources detected in the field,
of which only 4 belonging to the cluster.
The flaring source VA 479 is a field M
dwarf.
Time variability of Hyades and field stars
Conclusions and future work
•
XMM-Newton EPIC observations of open clusters and star forming
regions are providing new insights into the physics of magnetic activity in
stars.
•
With its combination of high sensitivity and good spectral resolution EPIC
observations (in combination with RGS observations for the brightest
sources) allow investigating the coronal properties of stars over a wide
range of ages (from a few million years to about 1 Gyr).
•
The GT observations discussed here, together with those of other GT and
GO programmes, are starting to cover the full age-metallicity plane of
nearby open clusters. They allow addressing the question whether a
cluster of a given age is representative of all clusters with the same age.
•
XMM-Newton is sensitive enough to allow also the investigation of coronal
emission in clusters older than 1 Gyr (e.g. solar-type stars in the 2 Gyr
cluster NGC 752 or active binaries in the 5 Gyr cluster M67).