A(r) - lamost

Mapping the 3D Galactic extinction &
extinction laws with LAMOST
-- applying the star pair method to large scale
spectroscopic and photometric surveys
Haibo Yuan (苑海波）
Beijing Normal University
Collaborators: Xiaowei Liu, Maosheng Xiang, Yang Huang, Bingqiu Chen
Thursday, July 14, 2016
Outline
• Motivations and Methods
• LAMOST data and results
• Summary
Thursday, July 14, 2016
Why do we care about extinction / law?
• Intrinsic SEDs (properties) of
astronomical objects
• Properties of dust
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Reddening determinations
Based on dust emission (SFD98 map; Planck dust map)
Accurate, full sky;
2D; low-resolution; normalization problem; disk region
Based on stellar absorption
Photometric methods
SED fitting method
Spectroscopic methods
stellar atmosphere models
star pair technique
Intrinsic color -- Teff relation
Others: e.g. bayesian method, EW(DIBs), N(HI)
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Stellar locus
A(r)
Stellar colors are determined
dominately by Teff,
weakly by [Fe/H] & Log g
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∆A(r)
3D extinction determined from XSTPS-GAC (g, r, i),
2MASS (J, H, Ks) and WISE (w1,w2) photometric data Chen et al. 2014
>6,000 deg2
140<l<240 deg
-60<b<40 deg
Resolution:3’-9’
Distance: 1-5 kpc
Green et al. 2015
(PS1)
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A(r)
∆A(r)
SDSS/LAMOST ... SDSS/2MASS/Xuyi/PS1/LSST ...
Spectroscopy
Photometry
Spectra
Stellar parameters
Mags., Colors
Gaia
Astrometry
Distances
With ~106 spectra, “identical” stars in different
environments (e.g., different extinction) can be easily
paired, then by comparing differences in
normalized spectra
colors
Interstellar absorption lines
DIBs as ʻfine structureʼ on the
DIBs
interstellar extinction curve
Nebular/stellar emission lines
Reddening & laws
6283A
Pros: Straight-forward, “model-free”, suitable for most stars
With spec.-phot. distances/Gaia, 3D information is added
Thursday, July 14, 2016
Normal spectrum, normal colors
Control star(s)
DIB 6283A
dust
clouds
Target star
Redder, with DIBs and other
interstellar absorption lines
Yuan & Liu, 2012; Yuan et al. 2013
With nebular emission lines
Yuan & Liu, 2013
PNe, SNR, HII regions
Active stars,
chemically particular stars
Color calibration of
un-calibrated field
With stellar emission lines
6283A
With systematic color differences
Yuan et al 2015
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Star-pair technique
Assumptions:
Stars of the same (Teff, Log g, [Fe/H]) parameters have the same
intrinsic colors and spectra
Within a narrow range (Teff:±5%, log g: ±0.5dex, [Fe/H]:±0.3dex),
intrinsic colors are linear function of Teff, Log g, [Fe/H]
Step 1: Define a control sample: E(B-V) < 0.05; S/N >20; good photometry
and reliable (Teff, Log g, [Fe/H]) parameters
Step 2: De-redden the control sample using the SFD map
Step 3: For a star of given (Teff, Log g, [Fe/H]), obtain its intrinsic colors
from the dereddened control sample to estimate its color excess
Step 4: Convert to E(B-V)
Multi control samples are needed to obtain reddening in multi-bands from
the UV to the IR
Advantages: straight-forward, model-free, suitable to most stellar types
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Reddening accuracy from the star pair method
Res. = 0.019 mag
Stripe 82
SNR > 20
∆g-r
∆u-g
Res. = 0.038 mag
E(B-V)SFD
E(B-V)SFD
Res. = 0.014 mag
∆r-i
∆i-z
Res. = 0.013 mag
E(B-V)SFD
E(B-V)SFD
Intrinsic colors/color excess of individual stars are accurate to 1- 4%
The technique is able to determine E(B-V) to an accuracy of 0.01 mag
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Empirical extinction law from ~ 104 SDSS/SEGUE stars
Yuan et al. 2013
Yuan, Liu & Xiang, 2013
E(i-z)
The Rv=3.1 Fitzpartrick law is preferred
to the Rv=3.1 O’Donnell law, but an
update in the UV and mid-IR is needed.
The SFD98 map over-estimates E(B-V)
by 14% (See also Schlafly & Finkbeiner 2011;
Schlafly et al. 2012);
E(g-r)
Obs/Mod
R(V)=3.1
--- R(V)=3.1 Fitzpartrick law ✔
--- R(V)=3.1 CCM law
R(V)
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Teff -- Intrinsic color relation method
Wang & Jiang 2014
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LAMOST sample (2011.10 - 2015.11)
GAC
6 M spectra and stellar parameters (2M in GAC), photometry from Galex (FUV,
NUV), SDSS (u,g,r,i,z), XSTPS-GAC/APASS (g,r,i), 2MASS (J,H,Ks), WISE (W1,
W2,W3,W4), reddening in many colors, distances, et al.
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Empirical reddening law from FUV to mid-IR with 106 LAMOST stars
FUV - NUV
NUV - u
u-g
g-r
r-i
i-z
z-J
Ks - W1
J-H
W1 - W2
H - Ks
W2 - W3
Independent, accurate
measurements of multi-band
reddening of 106 stars: ⎯ a
unique dataset to study the 3D
variations of reddening law
Is there a universal extinction
law from UV to mid-IR?
How do dust properties change
with position and environment?
W3 - W4
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NUV - g
i-J
How to correct extinction?
Spatial variations of extinction laws
median: 3.16
mean: 3.13
stddev: 0.4
R(V)
(120,50)
(230,-40)
R(V)
R(V)
R(V)
E(g-r)
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Slices of a 3D extinction map of the GAC from (spectr. + phot.)
Camelopardalis
(l,b)=(210,+30)
Tauras
Persus
(l,b)=(150,−30)
250 pc
2 kpc
Thursday, July 14, 2016
500 pc
1 kpc
4 kpc
SFD
北京大学物理学院天文学系
北京大学科维理天文与天体物理研究所
地址：理科二号楼2901 电话：6275 1134
http://vega.bac.pku.edu.cn/astro/astro.htm
地址：朗润园科维理楼 电话：6275 6692
http://kiaa.pku.edu.cn/
Applications of 3D extinction map
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•
Correcting for reddening and extinction for objects
embedded in the plane of the Galaxy
•
•
•
Studies of Galactic structure
Calibration of future emission-based dust maps
Determining distances to objects of known reddening
SNR Sim 147 as an example
G180.0-01.7
Size: 200 arcmin
Dist: 0.6 - 1.6 kpc
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“The S147 dust ring”
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Example lines of sight
20
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E(r-i)
E(J-H)
E(i-J)
E(H-Ks)
Varying extinction laws toward S147
E(g-r)
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E(g-r)
Summary
LAMOST provides a unique dataset to probe
the distribution and properties of Galactic
dust, based on ~6M stars,
•
We have obtained empirical extinction coefficients for the
Galex, SDSS，2MASS and WISE passbands
•
We have constructed a 2D R(V) map, extinction law varies
spatially
•
We have constructed a 3D map of extinction in the GAC
Thursday, July 14, 2016