PAIRITEL Photometry of Dwarfs from the IRAC GTO sample Joseph L. Hora Brian Patten, Massimo Marengo...

PAIRITEL Photometry of Dwarfs from the IRAC GTO sample

PAIRITEL Photometry of Dwarfs from the IRAC GTO sample

Joseph L. HoraBrian Patten, Massimo Marengo

Harvard-Smithsonian Center for Astrophysics

2nd Annual PAIRITEL Workshop

Joseph L. HoraBrian Patten, Massimo Marengo

Harvard-Smithsonian Center for Astrophysics

2nd Annual PAIRITEL Workshop

2006/05/16 – J. Hora 2nd Annual PAIRITEL Workshop

IRAC M/L/T Dwarf ProgramIRAC M/L/T Dwarf Program• IRAC bands at 3.6, 4.5, 5.8, and 8 μm• IRAC sensitivity, molecular features and continuum

sampled• Sample: 87 late M, L, T dwarfs, masses ~70 MJ – 15 MJ

• Chosen based on known sources in 2002– Trigonometric parallax– Well-determined spectral types– Located in uncrowded fields, not known binaries (although

some are now known or suspected)

• Sources of near-IR photometry are 2MASS, DENIS, SDSS– Possible problems in converting from other photometric

systems to 2MASS

• Near-IR photometry on this reference sample necessary to identify and classify additional M, L, T candidates

• IRAC bands at 3.6, 4.5, 5.8, and 8 μm• IRAC sensitivity, molecular features and continuum

sampled• Sample: 87 late M, L, T dwarfs, masses ~70 MJ – 15 MJ

• Chosen based on known sources in 2002– Trigonometric parallax– Well-determined spectral types– Located in uncrowded fields, not known binaries (although

some are now known or suspected)

• Sources of near-IR photometry are 2MASS, DENIS, SDSS– Possible problems in converting from other photometric

systems to 2MASS

• Near-IR photometry on this reference sample necessary to identify and classify additional M, L, T candidates


Molecular features in NIR Dwarf spectraMolecular features in NIR Dwarf spectra

• L dwarfs – absorption from CO and H2O, T dwarfs have broad absorption bands of CH4 and H2O, and H2 absorption– In near-IR photometry, M and L dwarfs become redder with

decreasing Teff in J −H and H−K.

– The L to T dwarf transition occurs as the silicate and iron condensates (clouds) become buried at increasing depth in late-L dwarfs.

– H2O absorption begins to dominate the near-IR spectrum, leading to a bluing of the near-IR colors through the early-T types.

• The colors then become even bluer from early-T to late-T with the onset and growth of CH4 absorption and H2 in K.

• The overall result is that the J−H and H−K colors for T dwarfs become bluer with increasing spectral subtype, becoming degenerate with the colors of higher mass K and M dwarfs.

• L dwarfs – absorption from CO and H2O, T dwarfs have broad absorption bands of CH4 and H2O, and H2 absorption– In near-IR photometry, M and L dwarfs become redder with

decreasing Teff in J −H and H−K.

– The L to T dwarf transition occurs as the silicate and iron condensates (clouds) become buried at increasing depth in late-L dwarfs.

– H2O absorption begins to dominate the near-IR spectrum, leading to a bluing of the near-IR colors through the early-T types.

• The colors then become even bluer from early-T to late-T with the onset and growth of CH4 absorption and H2 in K.

• The overall result is that the J−H and H−K colors for T dwarfs become bluer with increasing spectral subtype, becoming degenerate with the colors of higher mass K and M dwarfs.


M, L, T dwarf spectral features sampled by IRACM, L, T dwarf spectral features sampled by IRAC

• IRAC channel 1 includes much of the CH4 fundamental absorption band (~3.3 μm).

• Channel 2 includes the continuum peak present for all stars cooler than 3000 K, making this the most sensitive IRAC channel for the study of sub-stellar objects.

• Channel 2 also contains the broad but shallow CO fundamental absorption band (~4.7 μm), whose presence in the T dwarfs provides evidence for non-equilibrium chemistry models

• Channel 3 includes H2O absorption and, for low Teff , NH3 absorption.

• Channel 4 – molecular absorption due to CH4

• IRAC channel 1 includes much of the CH4 fundamental absorption band (~3.3 μm).

• Channel 2 includes the continuum peak present for all stars cooler than 3000 K, making this the most sensitive IRAC channel for the study of sub-stellar objects.

• Channel 2 also contains the broad but shallow CO fundamental absorption band (~4.7 μm), whose presence in the T dwarfs provides evidence for non-equilibrium chemistry models

• Channel 3 includes H2O absorption and, for low Teff , NH3 absorption.

• Channel 4 – molecular absorption due to CH4


IRAC bandpasses and dwarf spectraIRAC bandpasses and dwarf spectra


Color vs Spectral TypeColor vs Spectral Type

• IRAC-IRAC colors are slowly changing until L-T boundary

• Near-IR to IRAC colors show trends throughout the range of types

• Combination of all data allow better determination of object class

• IRAC-IRAC colors are slowly changing until L-T boundary

• Near-IR to IRAC colors show trends throughout the range of types

• Combination of all data allow better determination of object class


Goals of PAIRITEL Measurements Goals of PAIRITEL Measurements • Improved photometry

– Some targets close to sensitivity limits of original 2MASS, or SDSS or DENIS surveys

– Some photometry affected by nearby sources in field, due to high proper motion the stars are now better separated

• Variability monitoring– Variations for example due to uneven coverage of the surface

in CH4 or other types of weather which could cause changes in flux

– Rotation periods 1-10 hr have been detected in dwarfs– Presence of variations in T dwarfs not well established

• 2–17% variations observed by Artigau et al. 2003 in J & H• Others report monitoring with no variations detected

– PAIRITEL observations to sample at various frequencies of 1/night+ over months+ timescales

– IRAC continuous monitoring for hours of dwarfs saw no variability

– Cycle 3 GTO program to sample hours, weeks, months timescales

• Improved photometry– Some targets close to sensitivity limits of original 2MASS, or

SDSS or DENIS surveys– Some photometry affected by nearby sources in field, due to

high proper motion the stars are now better separated

• Variability monitoring– Variations for example due to uneven coverage of the surface

in CH4 or other types of weather which could cause changes in flux

– Rotation periods 1-10 hr have been detected in dwarfs– Presence of variations in T dwarfs not well established

• 2–17% variations observed by Artigau et al. 2003 in J & H• Others report monitoring with no variations detected

– PAIRITEL observations to sample at various frequencies of 1/night+ over months+ timescales

– IRAC continuous monitoring for hours of dwarfs saw no variability

– Cycle 3 GTO program to sample hours, weeks, months timescales


PAIRITEL Observation StatusPAIRITEL Observation Status

• 68 objects in program

• Observations started ~Jan 23 2006

• 24/35 done for objects where only 1 observation requested

• 24/33 of monitoring stars have at least one measurement

• Median number is 17 samples, most have goal of 50 samples

• 68 objects in program

• Observations started ~Jan 23 2006

• 24/35 done for objects where only 1 observation requested

• 24/33 of monitoring stars have at least one measurement

• Median number is 17 samples, most have goal of 50 samples


DWARF Program Observation History

0

2

4

6

8

10

12

14

16

18

1/23/03 2/6/03 2/20/03 3/6/03 3/20/03 4/3/03 4/17/03

Date

Nu

mb

er

of

Ob

jec

ts O

bs

erv

ed


Quick look at DWARF program dataQuick look at DWARF program data

• A couple stars with M<15 have been observed ~20 x

• Use pipeline mosaics– Poor weather data tossed out– All sources >10σ in each band found– Aperture photometry performed (iraf/phot task) on

sources– Bandmerge performed to generate J/H/K catalog– Catalog then matched to 2MASS data– Zero point adjustment determined to minimize median

difference between 2MASS and PAIRITEL photometry for all matched sources <15mag

• To obtain higher S/N, mosaics averaged and photometry performed as above on these frames

• A couple stars with M<15 have been observed ~20 x

• Use pipeline mosaics– Poor weather data tossed out– All sources >10σ in each band found– Aperture photometry performed (iraf/phot task) on

sources– Bandmerge performed to generate J/H/K catalog– Catalog then matched to 2MASS data– Zero point adjustment determined to minimize median

difference between 2MASS and PAIRITEL photometry for all matched sources <15mag

• To obtain higher S/N, mosaics averaged and photometry performed as above on these frames


DWARF 50

10

11

12

13

14

15

16

17

18

10 11 12 13 14 15 16 17 18

2MASS photometry

PA

IRIT

EL

ph

oto

me

try

Total J

Total H

Total K

DWARF 50

10

11

12

13

14

15

16

17

18

10 11 12 13 14 15 16 17 18

2MASS photometry

PA

IRIT

EL

ph

oto

me

try

Total J

Total H

Total K


DWARF 50

13.0

13.5

14.0

14.5

15.0

13.0 13.5 14.0 14.5 15.0

2MASS photometry

PA

IRIT

EL

ph

oto

metr

y

Total J

Total H

Total K


Single measurementsSingle measurements

• DWARF 50• DWARF 50

Filter 2MASS PAIRITEL

J 13.922 (0.026) 13.922 (0.034)

H 13.060 (0.024) 13.061 (0.040)

K 12.575 (0.028) 12.616 (0.041)

• DWARF 53• DWARF 53

Filter 2MASS PAIRITEL

J 15.494 (0.052) 15.663 (0.016)

H 15.524 (0.099) 15.826 (0.050)

K 15.518 (…….) 15.899 (0.105)


DWARF37 photometry

13.50

13.75

14.00

14.25

14.50

14.75

15.00

15.25

15.50

0 10 20 30 40 50 60 70 80

Days Since 2006/01/25

Ma

g

K

H

J

2MASS J

2MASS H

2MASS K

Ptotal J

Ptotal H

Ptotal K


12545506-0125328 (Reference Object) Photometry

13.50

13.75

14.00

14.25

14.50

14.75

15.00

15.25

15.50

0 10 20 30 40 50 60 70 80

Days Since 2006/01/28

Mag

K

H

J

2MASS J

2MASS H

2MASS K

Ptotal J

Ptotal H

Ptotal K


2MA1237+65272MA1237+6527


2MA1237+65272MA1237+6527

2MASS


2MA1237+65272MA1237+6527

PAIRITEL


2MASS 15394189-05204026 (P=G, 2MA=R)2MASS 15394189-05204026 (P=G, 2MA=R)


Next steps - Next steps -

• Refine photometry extraction – – Find optimal photometry parameters – radius,

background estimation, zero point adjustments– Confirm error estimate– Automate process

• Perform photometry on remainder of sample

• Perform frequency analysis

• Identify candidates that have variations or differences from 2MASS photometry

• Continue monitoring candidates

• Write up results

• Refine photometry extraction – – Find optimal photometry parameters – radius,

background estimation, zero point adjustments– Confirm error estimate– Automate process

• Perform photometry on remainder of sample

• Perform frequency analysis

• Identify candidates that have variations or differences from 2MASS photometry

• Continue monitoring candidates

• Write up results

PAIRITEL Photometry of Dwarfs from the IRAC GTO sample Joseph L. Hora Brian Patten, Massimo Marengo...

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