J/ApJ/933/54 IRTF/SpeX and Spitzer/IRS spectra of beta Pictoris (Lu+, 2022)
Trends in silicates in the β Pictoris disk.
Lu C.X., Chen C.H., Sargent B.A., Watson D.M., Lisse C.M., Green J.D.,
Sitko M.L., Mittal T., Lebouteiller V., Sloan G.C., Rebollido I.,
Hines D.C., Girard J.H., Werner M.W., Stapelfeldt K.R., Wu W., Worthen K.
<Astrophys. J., 933, 54 (2022)>
=2022ApJ...933...54L 2022ApJ...933...54L
ADC_Keywords: Spectra, optical; Spectra, infrared; Stars, A-type; Exoplanets
Keywords: Debris disks ; Silicate grains ; Planetary system formation ;
Exoplanet formation ; Planetesimals ; Exozodiacal dust ;
Spectroscopy ; Infrared astronomy
Abstract:
While β Pic is known to host silicates in ring-like structures,
whether the properties of these silicate dust vary with stellocentric
distance remains an open question. We re-analyze the β Pictoris
debris disk spectrum from the Spitzer Infrared Spectrograph (IRS) and
a new Infrared Telescope Facility Spectrograph and Imager spectrum to
investigate trends in Fe/Mg ratio, shape, and crystallinity in grains
as a function of wavelength, a proxy for stellocentric distance. By
analyzing a re-calibrated and re-extracted spectrum, we identify a new
18um forsterite emission feature and recover a 23um forsterite
emission feature with a substantially larger line-to-continuum ratio
than previously reported. We find that these prominent spectral
features are primarily produced by small submicron-sized grains, which
are continuously generated and replenished from planetesimal
collisions in the disk and can elucidate their parent bodies'
composition. We discover three trends about these small grains: as
stellocentric distance increases, (1) small silicate grains become
more crystalline (less amorphous), (2) they become more irregular in
shape, and (3) for crystalline silicate grains, the Fe/Mg ratio
decreases. Applying these trends to β Pic's planetary
architecture, we find that the dust population exterior to the orbits
of β Pic b and c differs substantially in crystallinity and
shape. We also find a tentative 3-5um dust excess due to spatially
unresolved hot dust emission close to the star. From our findings, we
infer that the surfaces of large planetesimals are more Fe-rich and
collisionally processed closer to the star but more Fe-poor and
primordial farther from the star.
Description:
We observe the β Pic system using NASA's IRTF Medium Resolution
SpeX in its short wavelength cross-dispersed (SXD;R∼2000,0.7-2.55um)
and long wavelength cross-dispersed (LXD; R∼2500,1.7-5.5um) modes on
2021 February 2 at 05:47:18 UT and 07:12:12 UT.
We use nearby (within 0.5deg and 0.1 in airmass) HD 37781 (A0V,
K=6.516) as a calibration standard to measure the atmospheric effects
on our observations of β Pic. We observe β Pic and HD 37781
in SXD mode with a total on-target integration time of 92s and 180s,
and in LXD mode for a total on-target integration time of 66s and
637s, respectively, at an airmass∼3. See Section 2.1.
We re-extract and re-calibrate the Spitzer IRS low-resolution
β Pic spectrum; originally published in Chen+ 2007ApJ...666..466C 2007ApJ...666..466C
and obtained on 2004 November 16.
IRS is an MIR spectrograph that covers 5.2-38um with low (R∼60-130)
and moderate (R∼600) resolution spectroscopic capabilities, and has
two operating modes: a mapping mode and a staring mode. For our work,
we focus on low-resolution observations of β Pic.
See Section 2.2.
Objects:
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RA (ICRS) DE Designation(s)
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05 47 17.08 -51 03 59.4 β Pic = * bet Pic
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
fig2.dat 47 2 List of FITS files; table added by CDS
sp/* . 2 The 0.7-4.2mu IRTF/SpeX spectrum and 5.2-38.2mu
Spitzer/IRS spectrum of β Pic in FITS format
(Data behind Figure 2)
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See also:
B/vsx : AAVSO International Variable Star Index VSX (Watson+, 2006-)
B/gemini : The Gemini Observation Log (CADC, 2001-)
VI/139 : Herschel Observation Log (Herschel Science Centre, 2013)
J/A+AS/114/247 : Limb-darkening coefficients for R I J H K (Claret+, 1995)
J/A+A/363/1081 : Non-linear limb-darkening law for LTE models (Claret 2000)
J/ApJS/154/673 : COBE DIRBE Point Source Catalog (Smith+, 2004)
J/ApJ/653/675 : Spitzer 24um photometry of A dwarfs (Su+, 2006)
J/PASP/122/162 : Direct imaging of exoplanets (Beichman+, 2010)
J/ApJ/745/147 : Binaries among debris disk stars (Rodriguez+, 2012)
J/A+A/542/A18 : βPic Harps radial velocity data (Lagrange+, 2012)
J/A+A/552/A119 : Planet-star and moon-planet interaction (Saur+, 2013)
J/ApJ/777/160 : NIR imaging survey for planets around MG stars (Biller+, 2013)
J/ApJS/208/9 : Intrinsic colors and temperatures of PMS stars (Pecaut+, 2013)
J/ApJS/211/25 : Spitzer/IRS debris disk catalog. I. (Chen+, 2014)
J/ApJ/798/87 : Spitzer/IRS debris disk catalog. II. (Mittal+, 2015)
J/AJ/149/11 : Spectra of candidate standard stars in mid-IR (Sloan+, 2015)
J/MNRAS/449/3160 : Stellar multiplicity and debris discs (Rodriguez+, 2015)
J/ApJ/823/108 : A dust model for bet Pic from 0.58 to 870um (Ballering+, 2016)
J/ApJ/826/171 : IR data of debris disk vs metallicity of stars (Gaspar+, 2016)
J/ApJS/225/15 : IR excess stars from Tycho-2 and AllWISE (Cotten+, 2016)
J/A+A/594/A59 : Far-IR lines in YSOs Herschel-PACS (Riviere-Marichalar+, 2016)
J/A+A/595/A31 : SAM detection limits of 8 debris disks (Gauchet+, 2016)
J/A+A/607/A25 : beta Pic HARPS spectrum (Vidal-Madjar+, 2017)
J/AJ/154/245 : Spitzer-detected debris disks (Meshkat+, 2017)
J/MNRAS/469/521 : CO gas content of debris discs predictions (Kral+, 2017)
J/ApJS/239/14 : Revised exoplanet radii from Gaia DR2 (Johns+, 2018)
J/A+A/627/A28 : beta Pic BRITE, bRing, SMEI light curves (Zwintz+, 2019)
J/A+A/625/L13 : TESS light curve of beta Pictoris (Zieba+, 2019)
J/A+A/633/A110 : K band spectrum of beta Pictoris b (GRAVITY+, 2020)
J/A+A/648/A15 : beta Pictoris photometry (Kenworthy+, 2021)
J/A+A/646/A132 : beta Pictoris debris disk image (Janson+, 2021)
J/A+A/657/A7 : Stellar & substellar companions from Gaia (Kervella+, 2022)
J/AJ/161/179 : Predicted positions of βPictoris b and c (Brandt+, 2021)
J/A+A/672/A114 : FITS images of HST debris disks (Ren+, 2023)
Byte-by-byte Description of file: fig2.dat
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Bytes Format Units Label Explanations
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1- 19 A19 --- File Name of the FITS file in subdirectory "sp"
22- 25 A4 --- Inst Instrument identifier ("IRTF" or "IRS")
28- 30 F3.1 um lam1 Wavelength lower range
31 A1 --- --- [-]
32- 35 F4.1 um lam2 Wavelength upper range
38- 47 A10 "Y/M/D" Date Observation date (UT)
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History:
From electronic version of the journal
(End) Katia van der Woerd [CDS] 08-Apr-2024