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. Hu é lamo (Laeff-INTA, Spain) H. Bouy (UC Berkeley) C. Torres (LNA, Brazil) C. Melo, M. Sterzik (ESO, Chile) G. Chauvin (LAOG, France) D. Barrado y Navascu é s (Laeff-INTA, Spain).

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Direct imaging of substellar objects around young and nearby stars the sacy sample

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 work
Motivation of this work nearby stars:

Direct images of Substellar/planetary companions

Observations are the only way to

discriminate betweenformation theories.

Put constraints to physical parameters:

1. Frequency of substellar objects in wide orbits

2. Characterize their atmospheres

3.Calibrateevolutionary models


Looking for star companion systems
Looking for star-companion systems nearby stars:

Companion to stars: We can assume similar distance/age

High spatial resolution

High contrast imaging

Adaptive Optics + Large telescope


What can we learn with ao imaging

AO ima & spec nearby stars:

Population of BD/planets in large orbits

Characterize the atmospheres of the objects

What can we learn with AO imaging?

Targets:

Late-type Field stars

~M p *sin(i)

orbital parameters

Chauvin et al. 2007


Ao imaging where to look

7 nearby stars:

8

9

log t

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

10 MJup @ 10 Myr



Confirmed substellar companions
Confirmed substellar companions nearby stars:

Chauvin et al. 2007


Confirmed substellar companions1

HN Peg nearby stars:

DH Tau

HD3651

AB Pic

~475 AU

~795 AU

~100 AU

~ 260 AU

~ 330 AU

Confirmed Substellar companions

  • Most of the substellar companionsto stars detected so far have been found at separations between 100-1000 AU.

Neuhauser et al. 2004

Itoh et al. 2005

Chauvin et al. 2005

Burgasser et al. 2005

Luhman et al. 2007

● 1 planetary-mass companion (substellar binary): sep~60 AU

Chauvin et al. 2005

● 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. 2007

Kasper et al. 2007

Biller et al. 2006

Masciadri et al. 2005


What is sacy what is the connection with substellar planetary searches
What is SACY? nearby stars: What is the connection with substellar/planetary searches?


The sacy survey
The SACY survey nearby stars:

  • 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 nearby stars: ROSAT Sources

  • SACY [Hip + TYC & (B-V)0.6]

  • Observed objects (not sources)

  • Data from literature

  • 9574

  • 1953

  • 1750

  • 150

The SACY project

G0 and later…

}

Li abundance

Radial and Rot. velocity

Lithium -- age estimation

Dynamical properties + Convergence method:

NEW MOVING GROUPS

NEW MEMBERS of known assoc.

  • Torres et al. have identified at least 14 young associations in the SACY database (there are five more possible associations to confirm…) .

Torres et al. 2006; Torres et al. 2007

Prime targets for AO surveys to detect subs./planet. companions


Our study
Our study nearby stars:

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
1. Search for substellar companions around SACY stars nearby stars:

AO survey started on 2006

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


Average properties
Average properties… nearby stars:

  • Most of them are M,K-type stars

  • Ages ~ 10 Myr

  • Hipparcos and/or UCAC2 Proper motions:

    (Confirm companions in 1-2 yrs)


Observations
Observations nearby stars:

  • 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

30 60 90 120 300 (AU) @ 60pc nearby stars:

10MJup

M* = 0.8 Msun,

10 Myr

Detection limits

Δmag ~ [email protected]

Average curve for IB 2.27



Results
Results nearby stars:

  • 67 detected sources around 12 stars

  • All of them around BPA and ECA members

  • 14 sources at separation < 5”

  • 2 new subarsecond stellar binaries


Results1
Results nearby stars:


Results2
Results nearby stars:

Targets at separations < 500 AU from host star:

4 in ECA

13 in BPA


Sep=0.13” @103 = 13.4 AU nearby stars:

10 MJup

20 MJup

The most interesting substellar candidates

I. ε Cha

Target:

K0 star from Є Cha

d=103 pc

Age=6 Myr

[email protected]= 391AU

Galactic latitude ~ -8 deg


The most interesting substellar candidates nearby stars:

I. ε Cha

Target:

G8 star from Є Cha

d=115 pc

Age=6 Myr

[email protected]= 185 AU

Companion Candidate:

Sep = 210 AU

Mass < 10 MJup

Galactic latitude ~ -8 deg


The most interesting substellar candidates nearby stars:

II. BPA

Target:

M1 star from β Pic

d= 54 pc

Age=10 Myr

[email protected]= 210 AU

3.9”

Companion Candidate:

Sep = 210 AU

Mass < 10 MJup

Galactic Latitude ~ -23 deg


The most interesting substellar candidates nearby stars:

II. BPA

Target:

M1 star from β Pic

d= 72 pc

Age=10 Myr

[email protected] pc= 126 AU

Galactic Latitude ~ -07 deg

Companion Candidate:

Sep = 126 AU

Mass ~10 MJup

1.7”


Ii lower centaurus crux lcc
II: Lower Centaurus Crux (LCC) nearby stars:

  • 11 new identified members

  • Distances: 73-110pc

  • Age ~ 8 Myr

    (Torres et al., in prep.)


Substellar comp. candidates in LCC nearby stars:

Results:

130 detected sources

25 at separations < 5”

4 new subarc. binaries

Galactic latitudes (~ 0–8 deg)


Substellar comp. candidates in LCC nearby stars:

40 MJup @300 AU

15 MJup @260 AU

Gal. Latitudes: ~02 deg


Subsamples i and ii nature of the companion candidates
Subsamples I and II: nearby stars: Nature of the companion candidates?

  • Wider companions (sep > 10 arcsec): BACKGROUND

  • cross-correlation with optical, near-IR catalogs

  • Closer companions (sep < 10 arcsec)

    Second epoch observations are needed… hopefully

    next semester


Iii m type stars from sacy
III: M-type stars from SACY nearby stars:

  • 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

AB Dor – 70 Myr nearby stars:

β Pic – 10 Myr

M-type stars from SACY

  • Lithium cannot be used as an age estimator since it is depleted too fast.

…but gives as a lower limit age ≥ 10Myr


M stars age diagnostics
M-stars: Age diagnostics? nearby stars:

- Comparison with Evol. Tracks

- Stellar activity

- Surface gravity


M type stars from sacy1
M-type stars from SACY nearby stars:

  • Comparison with evolutionary tracks

Song et al. 2003


M type stars from sacy2
M-type stars from SACY nearby stars:

  • Lx / Lbol as age diagnostic

Song et al. 2003


M type stars from sacy3

M nearby stars: ⓪

M-type stars from SACY

  • Surface Gravity can be used as an age indicator.


M type stars from sacy4
M-type stars from SACY nearby stars:

  • 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

He I lines nearby stars:

Substellar companion candidates to M-stars?

8.6” companion to a M1 star

Sep. ~ 500 AU @ 59pc

Mass ~ 20 MJup @ 70 Myr

A DB white dwarf ‘companion’ to a nearby star

Public Archives: the system is a common proper motion pair (obs from 1910 to 2006).

BUT

Colors not consistent with a Brown Dwarf

but with a White Dwarf.


Conclusions
Conclusions nearby stars:

SACY 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..)


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