J/AJ/168/166 Galactic center: high-PM stars magnitude analysis (Haggard+, 2024)
The Galactic center in color: measuring extinction with high-proper-motion
stars.
Haggard Z., Ghez A.M., Sakai S., Gautam A.K., Do T., Lu J.R., Hosek M.,
Morris M.R., Granados S.
<Astron. J., 168, 166 (2024)>
=2024AJ....168..166H 2024AJ....168..166H
ADC_Keywords: Galactic center ; Extinction ; Magnitudes ; Colors ;
Photometry, infrared
Keywords: Galactic center ; Interstellar dust extinction ; Extinction ;
Astrometry ; Multi-color photometry ; Near infrared astronomy
Abstract:
The Milky Way's central parsec is a highly extinguished region with a
population of high-proper-motion stars. We have tracked 145 stars for
∼10yr at wavelengths between 1 and 4um to analyze extinction effects
in color-magnitude space. Approximately 30% of this sample dims and
reddens over the course of years, likely from the motion of sources
relative to an inhomogeneous screen of dust. We correct previous
measurements of the intrinsic variability fraction for differential
extinction effects, resulting in a reduced stellar variability
fraction of 34%. The extinction variability subsample shows that the
extinguishing material has subarcsecond scales, much smaller
variations than previously reported. The observed extinction events
imply a typical cross section of 500 au and a density of around
3x104atoms/cm3 for the extinguishing material, which are
consistent with measurements of filamentary dust and gas at the
Galactic center. Furthermore, given that the stars showing extinction
variability tend to be more highly reddened than the rest of the
sample, the extinction changes are likely due to material localized to
the Galactic center region. We estimate the relative extinction
between 1 and 4um as AH:AK':AL'=1.67±0.05:1:0.69±0.03. Our
measurement of extinction at longer wavelengths --L'(3.8um)-- is
inconsistent with recent estimations of the integrated extinction
toward the central parsec. One interpretation of this difference is
that the dust variations this experiment are sensitive to --which are
local to the Galactic center-- are dominated by grains of larger
radius than the foreground.
Description:
We have tracked 145 high-proper-motion stars in the Galactic center
for ∼10yr at wavelengths between 1 and 4um. The fundamental data used
in this study are photometric measurements derived from images taken
as part of W. M. Keck Observatory's Galactic Center Orbits Initiative
(GCOI; PI: Ghez). All of the GCOI images are obtained with the laser
guide star adaptive optics system and the facility's near-infrared
camera (NIRC2) in its narrow-field mode (10"x10") using one of the
following three bandpass filters: H (λ0=1.633um,
Δλ0=0.296um), K' (λ0=2.124um,
Δλ0=0.351um), and L' (λ0=3.776um,
Δλ0=0.776um).
In this paper we report both new and a reanalyzes of L' observations
that took place between 2013 and 2022. We combine the resulting L'
photometry with photometric measurements through the H and K' filters
from Gautam+ 2024, J/ApJ/964/164 whose observations took place
between 2009 and 2022.
The L' observations span 17 nights, of which 10 are newly reported.
The remaining seven were first reported by
Witzel+ (2017ApJ...847...80W 2017ApJ...847...80W) and Ciurlo+ (2023ApJ...944..136C 2023ApJ...944..136C), and
are reprocessed here such that the analysis is consistent across our
entire data set. See Section 2.1.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 60 36 Characteristics of the variability sample that are
consistent with changing extinction
tableb1.dat 47 109 Characteristics of the variability sample that is
not consistent with changing extinction
tabled1.dat 39 246 L' photometry information and colors for all
non-variable stars
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See also:
J/A+A/426/81 : Kinematic analysis of the Minispiral (Paumard+, 2004)
J/A+A/433/117 : L- & M-band imaging of the Galactic Center (Viehmann+, 2005)
J/ApJ/643/1011 : Early-type stars in the GC (Paumard+, 2006)
J/ApJS/181/62 : Survey of young solar analogs (Metchev+, 2009)
J/A+A/511/A18 : NIR observations of stars near SgrA* (Schoedel+, 2010)
J/ApJ/718/810 : Astrometry & Photometry in Arches cluster (Stolte+, 2010)
J/ApJ/737/73 : Infrared extinction toward the GC (Fritz+, 2011)
J/ApJ/764/154 : Stellar populations in the central 0.5pc. I. (Do+, 2013)
J/A+A/562/A125 : OGLE-III SMC mass. stars VI light curves (Kourniotis+, 2014)
J/AJ/150/118 : YSOVAR IR photometry: IRAS 20050+2720 (Poppenhaeger+, 2015)
J/AJ/150/132 : JHK photometry of 1203 variables in ONC (Rice+, 2015)
J/A+A/592/A120 : Variable stars in NGC 6715 (Figuera Jaimes+, 2016)
J/A+A/588/A128 : Variable stars in globular clusters (Figuera Jaimes+, 2016)
J/ApJ/871/103 : Catalog of 563 stars in the Galactic Center (Gautam+, 2019)
J/A+A/631/A20 : GALACTICNUCLEUS JHKs survey. II. (Nogueras-Lara+, 2019)
J/ApJ/873/65 : Keck/NIRC2 obs. of the Galactic Center (Sakai+, 2019)
J/MNRAS/488/1282 : Var. dust emission by WC type Wolf-Rayets (Williams, 2019)
J/ApJ/964/164 : Binary star frac in GC: radial dependence (Gautam+, 2024)
Byte-by-byte Description of file: table2.dat tableb1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Star Stellar identifier
12- 15 F4.1 mag Kpmag [10/18.7] Mean K' band magnitude, <K'>
17- 19 F3.1 mag dKpmag [0.2/1.6] Change in K' band magnitude,
ΔK'
21- 25 F5.1 --- KpChi2 [3.7/265] Reduced χ2 variability
metric; See Equation (1) in section 3
27- 28 I2 --- dof [3/17] Degrees of freedom for (H-K') color
measurements
30- 34 F5.1 deg th(H-Kp) [41.3/148.2] Modeled slope in the CMD;
θH-K'
36- 39 F4.1 deg e_th(H-Kp) [0.8/33.1] Modeled slope uncertainty;
θH-K'
41- 43 F3.1 mag H-Kp [1.1/3.5] Expected mean color <H-K'> derived
from the slope fits
45- 47 F3.1 --- P(H-Kp) [0/1] Probability of membership to the
H-K' extinction Gaussian
49- 52 F4.1 deg th(Kp-Lp) [57.7/87.5]? Modeled slope in the CMD;
θK'-L' (only for Table 2)
54- 56 F3.1 deg e_th(Kp-Lp) [1.8/9.5]? Modeled slope uncertainty;
θK'-L' (only for Table 2)
58- 60 A3 --- Dip Dipping ("yes"= 9 occurrences;
only for Table 2) (1)
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Note (1): Of particular interest are extinction variability sources which
have "dipping" events --dimming and subsequent brightening associated
with changing extinction captured by the observation baseline-- which
can be used to derive the scale and density associated with the
extinguishing medium. Any source that has a light curve showing an
isolated fall and rise that can be fit with a Gaussian is identified
as dipping. See Section 5.3.
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Byte-by-byte Description of file: tabled1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Star Stellar identifier (1)
10- 14 F5.2 mag Lpmag [8.6/15.1] Mean apparent L' band magnitude
16- 19 F4.2 mag e_Lpmag [0.03/0.15] Uncertainty in L'mag
21- 24 F4.2 mag H-Kp [1.71/3.2] Mean (H-K') color
26- 29 F4.2 mag e_H-Kp [0.05/0.19] Uncertainty in H-K'
31- 34 F4.2 mag Kp-Lp [0.85/2.5] Mean (K'-L') color
36- 39 F4.2 mag e_Kp-Lp [0.05/0.17] Uncertainty in K'-L'
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Note (1): Variable stars are selected according to the reduced
chi-squared metric discussed in Section 3.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Robin Leichtnam [CDS] 21-May-2025