J/ApJ/704/898 Photometry of the Hercules dwarf galaxy (Sand+, 2009)
The star formation history and extended structure of the Hercules Milky Way
satellite.
Sand D.J., Olszewski E.W., Willman B., Zaritsky D., Seth A., Harris J.,
Piatek S., Saha A.
<Astrophys. J., 704, 898-914 (2009)>
=2009ApJ...704..898S 2009ApJ...704..898S
ADC_Keywords: Galaxies, photometry ; Galaxies, nearby
Keywords: galaxies: dwarf - Local Group
Abstract:
We present imaging of the recently discovered Hercules Milky Way
satellite and its surrounding regions to study its structure, star
formation history and to thoroughly search for signs of disruption. We
robustly determine the distance, luminosity, size, and morphology of
Hercules utilizing a bootstrap approach to characterize our
uncertainties. We derive a distance to Hercules via a comparison to
empirical and theoretical isochrones, finding a best match with the
isochrone of M92, which yields a distance of 133±6kpc. As previous
studies have found, Hercules is very elongated, with
ε=0.67±0.03 and a half-light radius of rh∼230pc. Using the
color-magnitude-fitting package StarFISH, we determine that Hercules
is old (>12Gyr) and metal-poor ([Fe/H]~-2.0), with a spread in
metallicity, in agreement with previous spectroscopic work. This
result is robust with respect to slight variations in the distance to
Hercules and mismatches between the observed Hercules color-magnitude
diagram and theoretical isochrones. We infer a total absolute
magnitude of MV=-6.2±0.4. Our innovative search for external
Hercules structure both in the plane of the sky and along the line of
sight yields some evidence that Hercules is embedded in a larger
stream of stars. A clear stellar extension is seen to the northwest
with several additional candidate stellar overdensities along the
position angle of Hercules out to ∼35' (∼1.3kpc).
Description:
Observations of Hercules were, with one exception, taken during 2008
May and June during normal operations of the Large Binocular Telescope
(LBT), fitted with the red and blue channels of the Large Binocular
Camera. The B- and V-band images for the central Hercules field were
taken during Science Demonstration Time (SDT) and were presented in
Coleman et al. (2007ApJ...668L..43C 2007ApJ...668L..43C). When necessary, we adopted
SDSS-DR6 photometry directly for stars brighter than and near the
saturation limit of a given LBT field (which depends both on the
observing conditions and point spread function). In this case, g and r
magnitudes are converted to B magnitudes via the relations found by
Jordi et al. (2006A&A...460..339J 2006A&A...460..339J).
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 77 24818 Hercules photometry - central field
table3.dat 63 43637 Hercules photometry - adjacent fields
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 I5 --- Seq Star identification number
7- 15 F9.5 deg RAdeg Right Ascension in decimal degrees (J2000)
17- 24 F8.5 deg DEdeg Declination in decimal degrees (J2000)
26- 30 F5.2 mag Bmag B band magnitude
32- 35 F4.2 mag e_Bmag Error in Bmag
37- 40 F4.2 mag AB B band extinction (1)
42- 46 F5.2 mag Vmag V band magnitude
48- 51 F4.2 mag e_Vmag Error in Vmag
53- 56 F4.2 mag AV V band extinction (1)
58- 62 F5.2 mag rmag r band magnitude
64- 67 F4.2 mag e_rmag Error in rmag
69- 72 F4.2 mag Ar r band extinction (1)
74- 77 A4 --- Obs [LBT/SDSS] Observed by SDSS or LBT
(Large Binocular Telescope)
--------------------------------------------------------------------------------
Note (1): extinction from Schlegel et al. (1998ApJ...500..525S 1998ApJ...500..525S) dust maps
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 I5 --- Seq Star identification number
7- 15 F9.5 deg RAdeg Right Ascension in decimal degrees (J2000)
17- 24 F8.5 deg DEdeg Declination in decimal degrees (J2000)
26- 30 F5.2 mag Bmag B band magnitude
32- 35 F4.2 mag e_Bmag Error in Bmag
37- 40 F4.2 mag AB B band extinction
42- 46 F5.2 mag rmag r band magnitude
48- 51 F4.2 mag e_rmag Error in rmag
53- 56 F4.2 mag Ar r band extinction
58 I1 --- F [1,4] Field number (1)
60- 63 A4 --- Obs [LBT/SDSS] Observed by SDSS or LBT
(Large Binocular Telescope)
--------------------------------------------------------------------------------
Note (1): Smoothed contour plots of Hercules and adjacent fields are
presented in figure 9: the contours show the 3, 4, 5, 7, 10, 15, and
20σ levels. Each row shows our Hercules pointings arranged from
East to West, with the middle panel roughly centered on the position
of Hercules. The top row shows contour plots after smoothing the data
by 2arcmin. The middle row is smoothed by 1.5arcmin, and the bottom
row is smoothed by 1arcmin.
--------------------------------------------------------------------------------
Nomenclature Notes:
Stars are <[SOW2009] NNNNN> in Simbad in table 2 or <[SOW2009] F NNNNN>
in table 3.
History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 22-Nov-2011