Direct imaging of substellar objects around young and nearby stars: The SACY sample
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Direct imaging of substellar objects around young and nearby stars:
The SACY sample
N. Huélamo (Laeff-INTA, Spain)
H. Bouy (UC Berkeley)C. Torres (LNA, Brazil) C. Melo, M. Sterzik (ESO, Chile) G. Chauvin (LAOG, France) D. Barrado y Navascués (Laeff-INTA, Spain)
Motivation of this workDirect images of Substellar/planetary companions
Observations are the only way to discriminate between formation theories.Put constraints to physical parameters:
1. Frequency of substellar objects in wide orbits
2. Characterize their atmospheres
3. Calibrate evolutionary models
Looking for star-companion systems
High contrast imaging
Companion to stars: We can assume similar distance/age
Adaptive Optics + Large telescope
High spatial resolution
What can we learn with AO imaging?
Chauvin et al. 2007
AO ima & specPopulation of BD/planets in large orbitsCharacterize the atmospheres of the objects
Targets: Late-type Field stars
~M p *sin(i)orbital parameters
AO imaging: Where to look….
• Substellar companions are normally searched around young ( < 100 Myr) and nearby (d < 100pc) late-type stars.
WHY? CONTRAST Young late-type stars: The younger the substellar object, the brighter
Nearby stars: we can probe smaller separations
7
log t
8 9
M primary (Msun)
△K(mag)
1.0 7.5
0.5 6.6
0.1 4.3
10 MJup @ 10 Myr
Deep surveys to detect substellar/planetary companions
SURVEYNumber Targets
Age (Myr)
Distance (pc)
Chauvin et al (2003)3.6/Adonis
24 < 30 ≤ 50
Masciadri et al. (2005) NACO/VLT
30 12-200 4-77
Biller et al. (2006)NACO/VLT + SDI
45 ≤ 250 ≤ 50
Kasper et al. (2007)NACO/VLT L-band
22 ≤ 30 ≤ 10 - 60
Lafreniere et al. (2007) Gemini+Altair
85 30 - 5000 ≤ 35
And more to come…
Confirmed substellar companions
Chauvin et al. 2007
Confirmed Substellar companions
• Most of the substellar companions to stars detected so far have been found at separations between 100-1000 AU.
~100 AU ~ 330 AU~ 260 AU ~795 AU~475 AU
HN PegHD3651DH TauAB PicNeuhauser et al. 2004Itoh et al. 2005Chauvin et al. 2005Burgasser et al. 2005 Luhman et al. 2007
● 1 planetary-mass companion (substellar binary): sep~60 AU
● No planets (or BDs) detected at very small separations No >2 Mjup at sep. 45-200 AU No >4 Mjup at sep. 20-40 AU No >5 Mjup at sep > 15 AU
Lafreniere et al. 2007Kasper et al. 2007Biller et al. 2006Masciadri et al. 2005
Chauvin et al. 2005
What is SACY?
What is the connection with substellar/planetary searches?
The SACY survey• Search for Associations Containing Young stars
Torres et al, 2003, Torres et al. 2006
- Started by Torres et al. in 2000 after the discovery of Tucana & Horologium (Torres et al. 2000, Zuckerman & Webb 2000)
Moving groups of Post- T Tauri stars: How to identify them? T Tauri Stars (Age ~1 Myr) Post-T Tauri stars (10-100Myr) Near-IR excess (disks) X-ray emission can persist.. Forbidden lines (accretion) Lithium X-ray emission, Lithium, etc… - Aim: Search for young and nearby stars as optical counterparts to X-
ray (ROSAT) detections
d ~30 pc, age~30 Myr
The SACY project
• Southern ROSAT Sources
• SACY [Hip + TYC & (B-V)0.6]
• Observed objects (not
sources)
• Data from literature
9574
1953
1750
150
Torres et al. have identified at least 14 young associations in the SACY database (there are five more possible associations to confirm…) .
Lithium -- age estimation
Dynamical properties + Convergence method: NEW MOVING GROUPS NEW MEMBERS of known assoc.
} Li abundanceRadial and Rot. velocity
Torres et al. 2006; Torres et al. 2007
Prime targets for AO surveys to detect subs./planet. companions
G0 and later…
Our study
1. VLT/NACO survey : Substellar/Planetary companions around new young nearby stars identified in the SACY survey
2. Characterization of nearby (young?) M-type stars in the SACY Catalog that do not belong to any moving group.
1. Search for substellar companions around SACY stars
The sample of 78 targets contains:
• I. 18 New identified members of 9 young and nearby loose associations included in Torres et al. 2007 (e.g. TW Hya, Beta Pic, Tuc-Hor)
• II. 30 New identified members in other nearby assocs. (e.g. LCC)
• III. 15 M-type stars without lithium and/or association but probably young…
• IV. 15 Young stars (with lithium) without association
AO survey started on 2006
Average properties…
• Most of them are M,K-type stars
• Ages ~ 10 Myr
• Hipparcos and/or UCAC2 Proper motions: (Confirm companions in 1-2 yrs)
Observations
• NACO/VLT • Optical WFS + IB2.27 filter• S27 objective : 27’’ x 27’’ FOV • Typical integrations of 12-15 minutes• Classical AO imaging• Service Observations (April-Sep. 2006)
Detection limits
M* = 0.8 Msun, 10 Myr
30 60 90 120 300 (AU) @ 60pc
10MJup
Average curve for IB 2.27
Δmag ~ [email protected]”
I: Nearby loose associations
Number Assoc. Age Distance
4 Є Cha 6 100
11 β Pic 10 60
3 Tuc-Hor 30 30
Results
• 67 detected sources around 12 stars• All of them around BPA and ECA members • 14 sources at separation < 5”• 2 new subarsecond stellar binaries
Results
Results
Targets at separations < 500 AU from host star: 4 in ECA 13 in BPA
The most interesting substellar candidates I. ε Cha
Target: K0 star from Є Chad=103 pcAge=6 Myr
Sep=3.8”@103pc= 391AU
10 MJup
20 MJup
Sep=0.13” @103 = 13.4 AU
Galactic latitude ~ -8 deg
The most interesting substellar candidates I. ε Cha
Target: G8 star from Є Chad=115 pcAge=6 Myr
Sep=1.8”@103pc= 185 AU
Galactic latitude ~ -8 deg
Companion Candidate: Sep = 210 AUMass < 10 MJup
The most interesting substellar candidates II. BPA
Target: M1 star from β Picd= 54 pcAge=10 Myr
3.9”
Companion Candidate: Sep = 210 AUMass < 10 MJup
Sep=3.9”@54pc= 210 AU
Galactic Latitude ~ -23 deg
The most interesting substellar candidates II. BPA
Target: M1 star from β Picd= 72 pcAge=10 Myr
1.7”
Companion Candidate: Sep = 126 AUMass ~10 MJup
Sep=1.7”@72 pc= 126 AU
Galactic Latitude ~ -07 deg
II: Lower Centaurus Crux (LCC)
• 11 new identified members• Distances: 73-110pc• Age ~ 8 Myr
(Torres et al., in prep.)
Galactic latitudes (~ 0–8 deg)
Substellar comp. candidates in LCC
Results:
130 detected sources25 at separations < 5”4 new subarc. binaries
Substellar comp. candidates in LCC
40 MJup @300 AU 15 MJup @260 AU
Gal. Latitudes: ~02 deg
Subsamples I and II:Nature of the companion candidates?
• Closer companions (sep < 10 arcsec) Second epoch observations are needed… hopefully next semester
• Wider companions (sep > 10 arcsec): BACKGROUND cross-correlation with optical, near-IR catalogs
III: M-type stars from SACY
• Our SACY sample contains 15 M-stars (M0-M3):
- With X-ray emission- Without lithium- Do not converge to any moving group- 8 (out of 15) with Hipparcos parallaxes: d ~(14-59 pc)
What is the nature of these stars?Are they young or old?
M-type stars from SACY
• Lithium cannot be used as an age estimator since it is depleted too fast.
AB Dor – 70 Myrβ Pic – 10 Myr
…but gives as a lower limit age ≥ 10Myr
M-stars: Age diagnostics?
- Comparison with Evol. Tracks
- Stellar activity
- Surface gravity
M-type stars from SACY
• Comparison with evolutionary tracks
Song et al. 2003
M-type stars from SACY
• Lx / Lbol as age diagnostic
Song et al. 2003
M⓪
M-type stars from SACY
• Surface Gravity can be used as an age indicator.
M-type stars from SACY
• Gravity sensitive lines:(e.g. Na I 5900 Å, KI D 7700 Å, Na I D 8200 Å)
• Method:- EW measurement of alkali lines- Comparison with templates: Younger and older stars with similar spectral types (on-going …)
Substellar companion candidates to M-stars?
A DB white dwarf ‘companion’ to a nearby star
8.6” companion to a M1 star
Sep. ~ 500 AU @ 59pcMass ~ 20 MJup @ 70 Myr
Public Archives: the system is a common proper motion pair (obs from 1910 to 2006). BUTColors not consistent with a Brown Dwarfbut with a White Dwarf.
He I lines
ConclusionsSACY Catalog contains prime targets for AO surveys to look for substellar and planetary-
mass companions: young and nearby
Preliminary results from our NACO/VLT survey:
• 17 good substellar/planetary companion candidates to nearby stars in nearby associations.
• Several candidates around LCC stars but …at very low galactic latitudes (probably background…)
• Second epoch observations necessary…
Increase the number of SACY young,nearby M-stars without association via optical, X-ray data (surface gravity, magnetic activity, etc..)