Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A downward revision to the distance of the 1806-20 cluster and
  associated magnetar from Gemini near-Infrared spectroscopy   We present H- and K-band spectroscopy of OB and Wolf-Rayet (WR) members of
the Milky Way cluster 1806-20 (G10.0-0.3), to obtain a revised cluster distance
of relevance to the 2004 giant flare from the SGR 1806-20 magnetar. From GNIRS
spectroscopy obtained with Gemini South, four candidate OB stars are confirmed
as late O/early B supergiants, while we support previous mid WN and late WC
classifications for two WR stars. Based upon an absolute Ks-band magnitude
calibration for B supergiants and WR stars, and near-IR photometry from NIRI at
Gemini North plus archival VLT/ISAAC datasets, we obtain a cluster distance
modulus of 14.7+/-0.35 mag. The known stellar content of the 1806-20 cluster
suggests an age of 3-5 Myr, from which theoretical isochrone fits infer a
distance modulus of 14.7+/-0.7 mag. Together, our results favour a distance
modulus of 14.7+/-0.4 mag (8.7^+1.8_-1.5 kpc) to the 1806-20 cluster, which is
significantly lower than the nominal 15 kpc distance to the magnetar. For our
preferred distance, the peak luminosity of the December 2004 giant flare is
reduced by a factor of three to 7 X 10^46 erg/s, such that the contamination of
BATSE short gamma ray bursts (GRB's) from giant flares of extragalactic
magnetars is reduced to a few percent. We infer a magnetar progenitor mass of
~48^+20_-8 Msun, in close agreement with that obtained recently for the
magnetar in Westerlund 1.

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The categories of this paper are: adap-org
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The categories of this paper are: stat
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The categories of this paper are: patt-sol
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The categories of this paper are: math-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: dg-ga
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The categories of this paper are: chao-dyn
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The categories of this paper are: chem-ph
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The categories of this paper are: hep-ph
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The categories of this paper are: econ
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The categories of this paper are: supr-con
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The categories of this paper are: q-alg
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The categories of this paper are: acc-phys
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The categories of this paper are: physics
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The categories of this paper are: math
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The categories of this paper are: ao-sci