Luca Pasquini – European Southern Observatory
description
Transcript of Luca Pasquini – European Southern Observatory
Luca Pasquini – European Southern Observatory
Piercarlo Bonifacio – Trieste Astronomical and Paris Observatories
Sofia Randich – Arcetri Astrophysical Observatory
Rolly Luigi Bedin – Space Telescope Science Institute
Katia BiazzoINAF – Catania Astrophysical
Observatory
(paper submitted to A&A)
True solar analogues in the open cluster M67True solar analogues in the open cluster M67
Specificity of our Sun & Solar System: How typical is the Sun as age, mass, and chemical composition? How typical is solar-type stars host planetary systems? Are the exo-planetary systems similar at all to our Solar System?The quest for solar analogues has been going on for a long time (review: Cayrel de Strobel 1996), and it became even more compelling after the discovery of the first exo-planets
(Mayor & Queloz 1995)
Recent results in the fieldfield: King et al. (2005): HD 143436 Meléndez et al. (2006): HD 98618 Meléndez & Ramirez (2007): HIP 56948 is the best solar twin known to date
What are the environments where we can find homogeneous age & chemical composition, common birth & early dynamical
environment?Open Clusters!
Introduction to the topics
Introduction to the topics
Why M67?Why M67?
Age (3.5-4.8 Gyr; Yadav et al. 2008) Chemical composition (in particular, metallicity: [Fe/H]=–0.03±0.03, 0.03±0.01, 0.02±0.03; Tautvaišiene et al. 2000, Randich et al. 2006, Pace et al. 2006) Lithium depleted G stars (Pasquini et al. 1997) Rich cluster
Other details: =08:51:18, =+11:48:00; l=215.696, b=+31.896 =1.05±1.96 mas (Hypparcos Catalogue) d≈950 pc E(B–V)=0.041±0.004 (Taylor 2007)
Photometry & Astrometry: 2 nights with WFI@MPG/ESO (B,V,I ; Yadav et al. 2008) Spectroscopy: 3 nights with FLAMES/GIRAFFE@VLT-ESO in MEDUSA mode (R≈17000; Pasquini, Biazzo et al. 2008)D
SS im
age: 6
0’
60
’
≈ 100 targets
Our 100 targets:13m≲V≲15m
0.60≲B–V≲0.75
Yadav et al. (2008)
Membership & Removal of binary stars
Membership & Removal of binary stars
Yadav’s Proper Motions (PMs)
Our Radial Velocities
Retaining the stars showing radial velocity (RV) variations < 1 km/s in three exposures and having mean RV within 2 (≈1.8 km/s) from the median cluster RV, we find 59 probable single RV members. Gaussian fit: <Vrad>=32.9 km/s, =0.73 km/s.
59 probable single RV members
Many of the retained stars tend to occupy the fainter side of the MS, where binaries are not expected to be present.On the other hand, our procedure still leaves several stars which are apparently binaries. This is because: the RV measurements are not of superb quality the observing time span is of only 18 days
From the initial sample of ≈100 lines, we have selected 6 line pairs sensitive to temperature and applied a method based on line-depth ratios (LDRs) to derive Teff of the probable members (Gray & Johanson 1991, Catalano et al. 2002, Biazzo et al. 2007).
Effective TemperatureEffective Temperature
Synthetic
spectrum at
5657 KSynthetic solar spectrum (5777
K) Synthetic
spectrum at
5867 K
5477 K
6050 K
GIRAFFE solar
spectrum
Line Depth RatiosLine Depth Ratios
HH wings wings
Calibration: Grid of synthetic spectra computed with SYNTHE 1D LTE model atmospheres computed with the ATLAS code (Kurucz 1993, 1995) Opacity Distribution Functions (Castelli & Kurucz 2003) with ξ=1 km/s, [Fe/H]=0, logg=4.4377, MLT=1.25, Teff=5450–6300 K
We have selected the spectral region in the range between 3 and 5 Å from the H line center as good Teff diagnostics (Cayrel et al. 1985; Fuhrmann et al. 1993; Barklem et al. 2002)
T LDR & T HT LDR & T H
Teff,๏LDR=5792±27 K Teff,๏
H=5717±100 K
Teff,๏Theor=5777 K (Wilson & Hudson
1991)Teff,๏
Phot=5730 K (Alonso et al. 1996)
10 Solar analogues:10 Solar analogues:<Teff
LDR>=–13 K (=60 K)<Teff
H>=–9 K (=58 K)
Lithium AbundanceLithium Abundance
NLi from curve of growth (COG) of Soderblom et al. (1993) NLTE effects from Carlsson et al. (1994)
Spread present for stars cooler than 6000 K Stars warmer than 6200 K have a decay (red side of the “Li-gap”?) Stars with Teff=6000-6200 K don’t show scatter
8 stars stand out of the MS, suggesting a parallel long-period binary sequence
not revealed by us
Solar TwinsSolar Twins
2410 starsYadav’s catalogue
59 starsRVs
750 starsYadav’s PMs
(P>60%, PM<6 mas/yr)
10 solar analoguesT LDR & T H& log(NLi)
(100 K)
5 solar twinsT LDR & T H& log(NLi)
(60 K)90 starsV & B–V
The core is not well reproduced due to: chromosphere NLTE effects
Solar Colour and Cluster Distance
Solar Colour and Cluster Distance
From our 10 solar analogues: B–V=0.692 (=0.020) and <V>=14.583 mag (=0.190)
Correcting for reddening: <B–V>0=0.651
Error estimate: our spread: 0.02/√10=0.006 [Fe/H] uncertainty: 0.007 photometry (Yadav et al. 2008): 0.008 cluster reddening uncertainty (Taylor 2007): 0.004 binaries!
Stellar evolution effects: [Fe/H]=0.01
B–VB–V Other determinationsOther determinations
0.658 Inverting our fit of all stars using T LDR
0.653 Inverting our fit of all stars using T H
~0.667 Old determinations: e.g., Barry et al. (1978)
0.62–0.64
Recent determinations: e.g., Holmberg et al. (2006)
→ <B–V>0=0.649±0.016
Correcting for reddening: <V>0=14.456 mag and <V>0–MV๏ (Bessell et al.
1998)=9.65 → <V>0–MV
๏=9.63±0.10
Error estimate: our spread: 0.19/√10=0.060 mag cluster reddening uncertainty (Taylor 2007): 0.012 mag [Fe/H] uncertainty: 0.05 mag
Stellar evolution effects: [Fe/H]=0.01
DistancDistance e
modulumoduluss
Other determinationsOther determinations
9.60 Sandquist et al. (2004)
9.61 An et al. (2007)
What we have done ...
What we have done ... What we are doing ...What we are doing ...
Solar twins in M67 (PM, RV, Teff, logNLi)
Solar colour
Cluster distance modulus
This work open the possibility to apply our
method to other clusters older and
younger than M67 for studies of stellar
evolution
We have observed some solar analogues with SOPHIE@OHP
We have submitted two proposals: HARPS@ESO & SOPHIE@OHP to monitor the “single stars”
We have submitted an UVES@ESO proposal to better define the stellar parameters of our 5 best solar twins
We plan to apply the method to other OCs