J/AJ/153/258 2007.5 to 2010.4 HST astrometry of HD 202206 (Benedict+, 2017)
HD 202206: a circumbinary brown dwarf system.
Benedict G.F., Harrison T.E.
<Astron. J., 153, 258-258 (2017)>
=2017AJ....153..258B 2017AJ....153..258B (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Planets ; Positional data ;
Parallaxes, spectroscopic ; Photometry, UBV ; Proper motions ;
Spectral types
Keywords: astrometry - binaries: general - brown dwarfs - planetary systems
Abstract:
Using Hubble Space Telescope Fine Guidance Sensor astrometry and
previously published radial velocity measures, we explore the
exoplanetary system HD202206. Our modeling results in a parallax,
πabs=21.96±0.12 milliseconds of arc, a mass for HD202206B of
MB=0.089-0.006^+0.007M☉, and a mass for HD202206c of
Mc=17.9-1.8+2.9MJup. HD202206 is a nearly face-on G + M binary
orbited by a brown dwarf. The system architecture that we determine
supports past assertions that stability requires a 5:1 mean motion
resonance (we find a period ratio, Pc/PB=4.92±0.04) and
coplanarity (we find a mutual inclination, Φ=6°±2°).
Description:
For this study astrometric measurements came from Fine Guidance Sensor
1r (FGS 1r), an upgraded FGS installed in 1997 during the second
Hubble Space Telescope (HST) servicing mission. It provided superior
fringes from which to obtain target and reference star positions
(McArthur et al. 2003hstc.conf..373M).
We utilized only the fringe tracking mode (POS mode) in this
investigation. POS mode observations of a star have a typical duration
of 60s, during which over 2000 individual position measures are
collected. The astrometric centroid is estimated by choosing the
median measure, after filtering large outliers (caused by cosmic-ray
hits and particles trapped by the Earth's magnetic field). The
standard deviation of the measures provides a measurement error. We
refer to the aggregate of astrometric centroids of each star secured
during one visibility period as an "orbit". Because one of the pillars
of the scientific method involves reproducibility, we present a
complete ensemble of time-tagged HD202206 and reference star
astrometric measurements, Optical Field Angle Distortion (OFAD;
McArthur et al. 2006hstc.conf..396M) and intra-orbit-drift-corrected,
in Table2, along with calculated parallax factors in R.A. and decl.
These data, collected from 2007.5 to 2010.4, in addition to providing
material for confirmation of our results, might ultimately be combined
with Gaia measures, significantly extending the time baseline of
astrometry, thereby improving proper motion and perturbation
characterization.
Our band passes for reference star photometry include: BVRI photometry
of the reference stars from the NMSU 1m telescope located at Apache
Point Observatory and JHK (from 2MASS; see Cutri et al. 2003, Cat.
II/246). Table4 lists the visible and infrared photometry for the
HD202206 reference stars. To establish spectral type and luminosity
class, the reference frame stars were observed on 2009 December 9
using the RCSPEC on the Blanco 4m telescope at Cerro Tololo
Inter-American Observatory (CTIO). We used the KPGL1 grating to give a
dispersion of 0.95Å/pix. Classifications used a combination of
template matching and line ratios. We determine the spectral types for
the higher S/N stars to within ±1 subclass. Classifications for the
lower S/N stars have ±2 subclass uncertainty. Table5 lists the
spectral types and luminosity classes for our reference stars.
Objects:
------------------------------------------------
RA (2000) DE Designation(s)
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21 14 57.77 -20 47 21.15 HD 202206 = HIP 104903
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File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 99 503 HD 202206 field astrometry
table3.dat 32 5 Astrometric reference stars
table4.dat 72 6 Visible and near-infrared photometry
table5.dat 36 4 Astrometric reference star initial
spectrophotometric parallaxes
table6.dat 47 6 HD 202206 and reference star relative positions
table7.dat 52 5 Reference star final proper motions, parallaxes,
and absolute magnitudes
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See also:
B/gcvs : General Catalogue of Variable Stars (Samus+, 2007-2012)
B/vsx : AAVSO International Variable Star Index VSX (Watson+, 2006-2013)
B/hst : HST Archived Exposures Catalog (STScI, 2007)
I/322 : UCAC4 Catalogue (Zacharias+, 2012)
I/317 : The PPMXL Catalog (Roeser+ 2010)
I/305 : The Guide Star Catalog, Version 2.3.2 (GSC2.3) (STScI, 2006)
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
I/254 : The HST Guide Star Catalog, Version 1.2 (Lasker+ 1996)
J/AJ/152/141 : Solar neighborhood. XXXVII. RVs for M dwarfs (Benedict+, 2016)
J/A+A/585/A5 : Exoplanet hosts/field stars age consistency (Bonfanti+, 2016)
J/ApJ/795/41 : HD128311 radial velocity and astrometric data (McArthur+, 2014)
J/AJ/142/187 : HST observations of 7 Pop.II variable stars (Benedict+, 2011)
J/A+A/519/A10 : Radial velocity curve of HD 202206 (Couetdic+, 2010)
J/A+A/390/267 : The CORALIE survey for extrasolar planets VIII (Udry+, 2002)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- Set [1/40] Data set (orbit) number (1)
4- 5 I2 --- Star [1/11] Star or reference star number
(1=HD202206, 5,6,9,10,11=astrometric reference
stars same as Table3) (2)
7- 15 A9 --- HST HST orbit and target identifier
17- 21 F5.2 mag Vmag [8.2/16] Hubble Space Telescope/Fine Guidance
Sensor (HST/FGS) V-band magnitude
23- 28 F6.2 deg V3 [0/293] Spacecraft+V3 axis roll angle
30- 39 F10.5 arcsec Xpos [-250/252] Optical Field Angle Distortion (OFAD)
X position (3)
41- 50 F10.5 arcsec Ypos [-149/96] Optical Field Angle Distortion (OFAD)
Y position (3)
52- 58 F7.5 arcsec e_Xpos [0.0015/0.007] Positional uncertainty in Xpos
60- 66 F7.5 arcsec e_Ypos [0.0014/0.039] Positional uncertainty in Ypos
68- 77 F10.4 d MJD [54285.6/55348.5] Modified Julian Date of
observation (JD-2400000.5)
79- 88 F10.7 --- Palpha [-1/1.03] Parallax factor in Right Ascension
90- 99 F10.7 --- Pdelta [-0.31/0.32] Parallax factor in Declination
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Note (1): We refer to the aggregate of astrometric centroids of each star
secured during one visibility period as an "orbit".
Note (2): As defined in Chapter 2, Fine Guidance Sensor Instrument Handbook
v.23.0, Nelan 2015,
http://www.stsci.edu/hst/fgs/documents/handbooks/instrumenthandbook/fgs_ihb.pdf
Note (3): The Optical Field Angle Distortion (OFAD) calibration (McArthur et al.
2006hstc.conf..396M) reduces Hubble Space Telescope (HST) and Fine Guidance
Sensors (FGS) as-built optical distortions of the order of 2s of arc to
less than one mas in the center of the FGS field of regard. This level of
correction persists for average radial distances from the FGS Field Of View
(FOV) center ≤100'', and is a reason the parallax error for K Pav
(±0.28mas, =117'') is over twice that of RR Lyr (±0.13mas,
=44'') (Benedict et al. 2011, Cat. J/AJ/142/187).
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- Star Reference star number
4- 13 F10.6 deg RAdeg Right Ascension in decimal degrees (J2000)
15- 24 F10.6 deg DEdeg Declination in decimal degrees (J2000)
26- 30 F5.2 --- Vmag [13.9/16] V-band magnitude (2)
32 I1 --- r_DEdeg [1/2] Source of position (1)
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Note (2): V magnitude, this paper.
Note (1): Position reference is defined as follows:
1 = PPMXL (Roeser et al. 2010, Cat. I/317), J2000;
2 = GSC2.3 (Lasker et al. 2008, Cat. I/305).
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Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- Star Star or reference star number
4- 8 F5.2 mag Vmag V-band magnitude
10- 13 F4.2 mag e_Vmag Error in V-band
15- 18 F4.2 mag B-V The B-V color index
20- 23 F4.2 mag e_B-V Error in B-V
25 A1 --- f_B-V Flag 'a' for B-V estimated from 2MASS photometry
27- 32 F6.3 mag Kmag ? 2MASS K-band magnitude
34- 38 F5.3 mag e_Kmag ? Error in Kmag
40- 44 F5.3 mag J-H ? The 2MASS (J-H) color index
46- 50 F5.3 mag e_J-H ? Error in J-H
52- 56 F5.3 mag J-K ? The 2MASS (J-K) color index
58- 62 F5.3 mag e_J-K ? Error in J-K
64- 67 F4.2 mag V-K ? The (V-K) color index
69- 72 F4.2 mag e_V-K ? Error in V-K
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Byte-by-byte Description of file: table5.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- Star Reference star number
4- 8 A5 --- SpT Spectral type (1)
10- 14 F5.2 mag Vmag [13.9/16] V-band magnitude
16- 18 F3.1 mag VMag [5.1/6.3] Absolute V-band magnitude
20- 23 F4.1 mag m-M [8/10.9] Distance modulus
25- 28 F4.2 mag AV [0/0.06] Interstellar V-band absorption
30- 32 F3.1 mas plx [0.7/2.5] Initial absolute spectrophotometric
parallax
34- 36 F3.1 mas e_plx [0.2/0.6] Error in plx
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Note (1): Spectral types and luminosity class estimated from classification
spectra, colors, and a reduced proper motion diagram (Figures 3 and 4).
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Byte-by-byte Description of file: table6.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- Star Star or reference star number
3 A1 --- f_Star Flag 'b' on Star 9 (R.A.=318.689335,
decl.=-20.788494, J2000)
5- 9 F5.2 mag Vmag V-band magnitude
11- 20 F10.5 arcsec ksi Relative position rolled to Right Ascension
(ξ) (1)
22- 28 F7.5 arcsec e_ksi Error in ksi
30- 39 F10.5 arcsec eta Relative position rolled to Declination
(η) (1)
41- 47 F7.5 arcsec e_eta Error in eta
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Note (1): Epoch 2008.4085 (J2000). Roll uncertainty ±.06°.
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Byte-by-byte Description of file: table7.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- Star Reference star number
4- 8 F5.2 mag Vmag V-band magnitude
10- 15 F6.2 mas/yr pmRA Relative proper motion in Right Ascension (3)
17- 20 F4.2 mas/yr e_pmRA Error in pmRA (3)
22- 27 F6.2 mas/yr pmDE Relative proper motion in Declination (3)
29- 32 F4.2 mas/yr e_pmDE Error in pmDE (3)
34- 37 F4.2 mas plx Absolute parallax (3)
39- 42 F4.2 mas e_plx Error in plx (3)
44- 47 F4.2 mag VMag Absolute V-band magnitude (3)
49- 52 F4.2 mag e_VMag The 1σ error in VMag (3)
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Note (3): Results of the radial velocity values from Couetdic et al. 2010
(Cat. J/A+A/519/A10) and Hubble Space Telescope (HST) astrometry (Table2)
modeling (see Section 2.4 in the paper for additional details).
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History:
From electronic version of the journal
(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 24-Aug-2017