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 ~ 7mag@0.5”

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..)