Brown dwarfs in UKIDSS

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Brown dwarfs in UKIDSS

Seminar @ Lyon, 16-20 April 2007

Nicolas Lodieu

Nigel Hambly, Paul Dobbie, Niall Deacon, Simon Hodgkin, Richard Jameson

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Collaborators

Nigel Hambly (Edinburgh) Paul Dobbie (AAO)

Richard Jameson (Leicester) Niall Deacon (Nijmegen)

Simon Hodgkin (Cambridge)

David Barrado y Navascués (Madrid) Eduardo Martin (IAC)

Maria Rosa Zapatero Osorio (IAC) Rafael Rebolo (IAC)

Victor Béjar (IAC)

Giovanni Carraro (Padova) Tim Kendall (Hertfordshire) Mark McCaughrean (Exeter) Ralf-Dieter Scholz (Potsdam) Hans Zinnecker (Potsdam)

David Pinfield (Hertfordshire) Sandy Leggett (Gemini)

Phil Lucas (Hertfordshire)

Ben Burningham (Hertfordshire) Steve Warren (Imperial, London) Daniel Mortlock (Imperial, London) Bram Venemans (Cambridge)

Emmanuel Caux (Toulouse) Alain Klotz (Toulouse)

Jean-Louis Monin (Grenoble) Jerome Bouvier (Grenoble) Estelle Moraux (Grenoble)

and the Cool Dwarf Science Working Group

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Background & Interests

Background:

Scientific interests:

Publications:

➢ University studies at the University of Bordeaux I

➢ DEA in Bordeaux & Toulouse in 2000

➢ PhD in Potsdam/Toulouse through FP5 programme (2000-2004)

➢ Post-doc at Leicester with Richard Jameson from 2004 to 2006

➢ Post-doc at the IAC from December 2006

➢ Nearby brown dwarfs in proper motion and wide-field surveys

➢ Brown dwarfs in open clusters: Pleiades, Alpha Per, Usco, Sigma Ori

➢ Study of the substellar IMF

➢ Brown dwarf binaries

➢ Subdwarfs

➢ 20 refereed articles

➢ 8 refereed articles as first authors

➢ 4 (2+2) papers submitted to MNRAS

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Outline of my talk

1. What is a brown dwarf?

2. Overview of techniques and searches to find brown dwarfs 3. Why do we study the substellar IMF?

4. The UKIRT Infrared Deep Sky Survey, UKIDSS 5. Highlights of the UKIDSS Large Area Survey

6. Highlights of the UKIDSS Galactic Cluster Survey 7. The Pleiades: the GCS results

8. Future work and perspectives

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Brown dwarfs

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The realms of brown dwarfs

 Brown dwarfs have masses < 0.072 M

_⊙

at solar metallicity

(Baraffe et al. 1998)

 Core temperature and pressure insufficient to ignite hydrogen

 Luminosity and temperature decrease inexorably with time

 Radii of extrasolar planets larger than those of brown dwarfs

 If M > 0.013 M

_⊙

brown dwarfs burn deuterium

 If M > 0.065 M

_⊙

brown dwarfs burn lithium shortly

 Atmospheres composed of H, He, C, O, N 10

^-2

6x10

^-6

1 Myr 2800

1 Gyr

L (L

_⊙

) T

_eff

(K)

1900

R (R

_jup

)

4.3

1.0 0.03 M

_⊙

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The formation of brown dwarfs

 Controversy over the formation mechanisms of brown dwarfs

 Jeans mass in molecular clouds larger than the mass of a brown dwarf

 Accretion should be interrupted to keep the mass below 0.072 M_⊙

 Proposed formation mechanisms

 Observational tests

➢ Brown dwarfs and stars share the same formation mechanism in disagreement with N-body simulations (Kroupa 2001)

 Turbulence in molecular clouds

 Irradiated pre-stellar cores

 Disk instabilities

 Ejection of the least massive component from multiple systems

 Formation in circumstellar disks Papaloizou & Terquem (2001) Armitage & Bonnell (2002)

Klessen (2001); Padoan & Nordlund (2002)

Reipurth & Clarke (2001) Whitworth & Zinnecker (2003) Boss (1998, 2000); Li (2002);

Watkins et al. (1998a, 1998b); Boffin et al. (1998)

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Searches for brown dwarfs I



First unambiguous brown dwarfs discovered in 1995

Nakajima et al. (1995) Rebolo et al. (1995)



Isolated brown dwarfs in the field

 All-sky surveys:

 Proper motion surveys:

 2MASS (Kirkpatrick et al. (2000)

 DENIS (Delfosse et al. 1997, 1999)

 SDSS (Fan et al. 2002; Schneider et al. 2002)

 UKIDSS (Kendall et al., 2007; Lodieu et al., 2007; Warren et al. 2007)

 LHS and NLTT catalogues (Luyten 1979, 1980)

 Solar vicinity within 8 pc (Reid and collaborators)

 Extension of the NLTT catalogue (L

é

pine and collaborators)

 Calán-ESO database (Ruiz et al. 1997)

 Liverpool-Edinburgh catalogue (Pokorny, Jones & Hambly 2003)

 Our proper motion survey (Scholz et al. 2000; Lodieu et al. 2005)

 Serendipitous discoveries:

 Cuby et al. 1999; Liu et al. 2002; Kendall et al. 2003

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Searches for brown dwarfs II



Brown dwarfs as companions to stars

 High-resolution imaging with adaptive optics

 Binary fraction 10-30%

 Separations < 20 AU with a peak around 4-8 AU

 Mass ratios around unity

 Radial velocity surveys

 High-resolution imaging with the Hubble space telescope

Close et al. (2002, 2003); Freed et al. (2003);

McCaughrean et al. (2004)

Martín et al. (1999); Reid et al. (2001); Burgasser et al. (2003);

Gizis et al. (2003); Bouy et al. (2003)

Mayor et al. (1992); Tokovinin et al. (1994); Mazeh et al. (1996) Marcy et al. (1999), Udry et al. (2002)

=> Less than 0.5% of solar type stars have BD companions

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

Brown dwarfs in star-forming regions:

Searches for brown dwarfs III



Brown dwarfs in young open clusters:

 Trapezium Cluster (Muench et al. 2002; Slesnick et al. 2004)

 Sigma Orionis (B

é

jar et al. 2001; Barrado y Navascu

é

s et al. 2004a)

 IC 348 (Luhman et al. 2003)

 Taurus (Briceño et al. 2002)

 Rho Ophiuchus (Luhman et al. 2000)

 Chameleon (Comerón et al. 1999, 2000)

 Serpens (Lodieu et al. 2002; Klotz et al. 2004)

 Pleiades (Martín et al. 1998; Dobbie et al. 2002; Moraux et al. 2003)

 Alpha Per (Barrado y Navascués et al. 2002)

 IC 2391 (Barrado y Navascués et al. 2004b)

 NGC 2547 (Jeffries et al. 2004)

 IC 4665 (de Wit et al. 2005)

 Collinder 359 (Lodieu et al. 2005)

 Determination of the IMF in the substellar regime

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The Initial Mass Function

●

Definition of the IMF :

Salpeter definition: ξ(logM) = dN / dlogM M

^-x

Mass spectrum definition ξ(m) = dN / dM M

^-α

●

Determination of the IMF :

{

^➢

M > 1 M

_⊙

α = 2.7

➢

M = 1-0.5 M

_⊙

α = 2.2

➢

M = 0.5-0.08 M

_⊙

α = 1.3

➢

M < 0.08 M

_⊙

α = 0.5-1.0

●

Understand the origin of stars and brown dwarfs

Kroupa 2002

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The UKIRT Infrared Deep Sky Survey

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UKIDSS

➔

New wide-field NIR survey with WFCAM on UKIRT

(Lawrence et al. 2006)

➔

Pipeline-processed by CASU in Cambridge

(Irwin et al. 2007, in prep)

➔

WFCAM Science Archive

(Hambly et al. 2007, in prep)

➔

5 components: LAS, GCS, GPS, DXS, and UDS

➔

Typical 5 sigma completeness limit is K ~ 18.0 mag (Vega)

➔

3 Data Releases: EDR, DR1, DR2plus

(Dye et al. 2006; Warren et al. 2007)

➢

Galactic Cluster Survey (GCS)

➔

ZYJHK observations

➔

1000 square degrees

➔

10 star-forming regions and open clusters

➔

2 epochs in the K-band

➔

5 sigma completeness limits: Z ~ 20.0, J ~ 18.6, K ~ 17.5 mag

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Highlights from the UKIDSS

Large Area Survey

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New late-T dwarfs in the LAS DR1

✔ Eight new T4.5-T7.5 dwarfs in LAS DR1

✔ One T4 dwarf recovered

✔ Distance between 15 and 85 pc

✔ Expected number of T dwarfs in the LAS after completion consistent with numerical simulations

✔ The coolest T dwarf known to date

✔ Two new T dwarfs found in DR2plus

UKIDSS LAS DR1

✔ Release in July 2006

✔ 190 square degrees

✔ (Y-J) > 0.5 AND (J-H) < 0.0

✔ J brighter than 19.0 mag

Lodieu et al. 2007, MNRAS, accepted

Results:

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ULAS0034, the coolest known T dwarf

✔ Spectral type T8.5±0.5

✔ Teff = 650±50 Kelvins

✔ (log g,M/H) = (4.5,0.0) or (5.0,+0.3)

✔ Age = 0.5-3 Gyr

✔ Photometric distance of 14-21 pc

✔ Tangential velocity of about 30 km/s

Analysis:

Characteristics of ULAS J0034:

✔ Y=18.90, J=18.15, H=18.49, K=18.48

✔ Optical z=21.91

✔ Mid-IR: 3.55^µm=16.28, 4.5^µm=14.49

✔ Proper motion of 0.37±0.07 mas/yr

Warren et al. 2007, MNRAS, submitted

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A new high-redshift quasar

Venemans et al. 2007, MNRAS, 376, L76

✔ LAS: Y=20.40, J=19.98, K=19.21

✔ SDSS co-adds: i=23.7, z=20.9

✔ All magnitudes in the Vega system

ULAS J020332.38+001229.2:

Results:

✔ Redshift z=5.864±0.003

Additional observations:

✔ ESO NTT EMMI z-band

✔ VLT FORS2 600z holographic grism

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Highlights from the UKIDSS

Galactic Cluster Survey

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The Upper Sco cluster (I)

1) Scorpius Centaurus = nearest OB association {

^✗ Upper Scorpius

✗ Upper Centaurus Lupus

✗ Lower Centaurus Crux

Blaauw (1964)

➢

Area ~ 120 square degrees

➢

Age = 5 Myr (kinematic + isochrone fitting)

➢

Distance = 145 pc (Hipparcos)

➢

Region free of extinction (Av < 2 mag)

2) Previous surveys:

✔

X-rays studies

(Walter et al. 1994; Preibisch et al. 1998, Argiroffi et al. 2006)

✔

Hipparcos astrometry

(de Bruijne 1997)

✔

Deep optical (RI) surveys

(Ardila et al. 2000, Slesnick et al. 2006)

✔

Optical (I) + near-infrared (JK)

(Martin et al. 2004)

✔

Near-infrared (ZYJHK): UKIDSS GCS SV+EDR

(Lodieu et al. 2006, 2007)

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The Upper Sco cluster (II)

Lodieu et al. 2006, 2007

Mass function best fit by a single power law of index α=0.6±0.1 over the 0.3-0.01 Msun mass range

Selection in the (Z-J,Z) diagram

Further rejection using the Y-J and J-K colours Proper motion 2MASS vs GCS

129 cluster candidates down to 8 Mjup

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The Sigma Ori cluster

Characteristics of the cluster:

σ Ori in the GCS DR1:

✔ Over 1.5 square degree radius

✔ Observations in ZYJHK

✔ Cluster sequence well defined

✔ Masses down to the deuterium limit

=>

Work in progress with the group at the IAC to combine optical/infrared photometry as well as spectroscopy

✔ Belongs to Orion OB 1b

✔ Age = 3-8 Myr

✔ Distance = 352 pc (Hipparcos)

✔ Little reddening

✔ X-ray emission from the cluster

✔ Large number of low-mass stars, BDs and planetary-mass objects

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The Pleiades open cluster

Lodieu, Dobbie, Deacon, Hodgkin, Hambly, Jameson 2007, MNRAS, in prep

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Pleiades: overview

✔

d = 130 pc

✔

Age = 125 Myr

✔

E(B-V) = 0.03

✔

PM = (+19.7,-45.5) mas/yr

Teide+Calar

(Rebolo, Martin, Zapatero Osorio)

SuperCOSMOS

(Deacon & Hambly 2004)

CFHT

(Bouvier, Moraux)

INT

(Dobbie, Pinfield, Jameson) and many other surveys...

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Pleiades: selection of candidates

➢ Point sources

➢ Z = 12.0-21.5 mag

➢ 105092 sources in ~12 sq. deg.

➢ 0.6-0.03 Msun mass range

The Pleiades in the GCS:

Selection procedure:

➢ Conservative photometric selection

➢ Derive proper motions for bright &

faint sources

➢ Derive membership probabilities for both samples

➢ Derive luminosity and mass functions for members with probabilities

➢ Extract high-probability members

➢ Select new photometric members outside the optical coverage

➢ Identify lower mas brown dwarfs in the (Y-J,Y) and (J-K,J) diagram

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Pleiades: coverage

GCS coverage: 12 sq. deg. CFHT + INT coverage

=> Large number of stellar and substellar with accurate

optical-to-infrared proper motions

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Pleiades: proper motion & probabilities

Bright sources: 2MASS vs GCS Faint sources: (INT+CFHT) vs GCS Membership probabilities calculated using the method described in Deacon &

Hambly (2004). Cluster and field star contributions modelled as a gaussian and a gaussian with declining exponential. Several magnitude bins used to compute membership probabilities from Z=12.0 to Z=21.5 mag.

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Pleiades: new faint candidates

1) No Z detection

2) Y = 18.5-21.0 mag

3) Line (Y-J,Y)=(0.75,18.5) to (1.5,21.0)

1) No Z and Y detection 2) J = 17.5-18.9 mag

=> Only one source with good PM

=> faintest candidate could be a L8

=> 5 have the Pleiades proper motion

=> 7 candidates fit the cluster sequence

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Pleiades: binary fraction

Selection of photometric multiple systems from the (Y-K,Y) CMD BF = N_B/(N_S+N_B) = 23/(40+23) = 36.5±4.0%

BF = 8/(14+8) = 36% for PM members only over the 0.075-0.030 M_☉ mass range

Bouy et al. (2006): 9-26%; Pinfield et al. (2000): 40-60%; Maxted & Jeffries (2005): 32-42%;

Basri &Reiners (2006): 26±10%; Field dwarfs (Burgasser et al. 2007): 10-30%

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Pleiades: Mass function

➢

N

umber of candidates with membership probabilities is 1064

➢ About 100 BDs in this sample

➢ Z = 12.0-21.5 mag

➢ Mass range = 0.560-0.035 Msun

➢ NextGen+DUSTY models @ 120 Myr

➢ Sum of probabilities for each 0.5 mag bin

The cluster mass function:

Results:

=> Results consistent with previous

determinations of the Pleiades mass function

(Martin et al. 1998; Hambly et al. 1999;Tej et al. 2002;

Moraux et al. 2003; Deacon & Hambly 2004; Chabrier 2003)

1) M=0.563-0.333 Msun α₁=+0.98±0.87 2) M=0.333-0.116 Msun α₂= -0.18±0.24 3) M=0.116-0.035 Msun α₃= -2.11±1.87

=> Lognormal fit with m_core=0.24 Msun

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Future plans and outlook

● UKIDSS is well underway with 3 data releases

● New late-T dwarfs and a high-redshift quasar discovered in the LAS

● The coolest T dwarf found to date

● Excellent results in young open clusters

● Await second epoch for the Hyades and Alpha Per

● Work in IC4665 to cross-correlate with the CFHT Key Programme

1) The UKIRT Infrared Deep Sky Survey:

2) Pleiades: summary

● Wide-field coverage in five passbands

● Proper motions down to 0.03 Msun

● New photometric brown dwarf candidates

● Mass function consistent with previous determinations over similar mass range

● Binary fraction of 33-40% in the 0.075-0.030 Msun mass range

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Future plans and outlook

● The full coverage will be provided by the GCS

● 2^nd epoch in K to get proper motion

● Optical multi-fibre spectroscopic follow-up with AAT/AAOmega

● Near-infrared spectroscopy with Gemini/GNIRS

● Adaptive optics Laser Guide Star to look for BD companions

● Deeper optical Z data to find lower-mass brown dwarfs

● Study gravity as a function of age with high-resolution spectroscopy

● Compare theoretical models to infrared spectra of young BDs

3) Pleiades and Upper Sco: future work

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