J/ApJ/778/L13 Subaru new Ca filter transmission function (Lee+, 2013)
Two distinct red giant branch populations in the globular cluster NGC 2419 as
tracers of a merger event in the Milky Way*.
Lee Y.-W., Han S.-I., Joo S.-J., Jang S., Na C., Okamoto S., Arimoto N.,
Lim D., Kim H.-S., Yoon S.-J.
<Astrophys. J., 778, L13 (2013)>
=2013ApJ...778L..13L 2013ApJ...778L..13L
ADC_Keywords: Photometry, calcium triplet
Keywords: Galaxy: formation; globular clusters: general;
globular clusters: individual: NGC 2419; stars: abundances
Abstract:
Recent spectroscopic observations of the outer halo globular cluster
(GC) NGC 2419 show that it is unique among GCs, in terms of chemical
abundance patterns, and some suggest that it was originated in the
nucleus of a dwarf galaxy. Here we show, from the Subaru narrowband
photometry employing a calcium filter, that the red giant branch (RGB)
of this GC is split into two distinct subpopulations. Comparison with
spectroscopy has confirmed that the redder RGB stars in the
hk[=(Ca-b)-(b-y)] index are enhanced in [Ca/H] by ∼0.2dex compared to
the bluer RGB stars. Our population model further indicates that the
calcium-rich second generation stars are also enhanced in helium
abundance by a large amount (ΔY=0.19). Our photometry, together
with the results for other massive GCs (e.g., ω Cen, M22, and
NGC 1851), suggests that the discrete distribution of RGB stars in the
hk index might be a universal characteristic of this growing group of
peculiar GCs. The planned narrowband calcium photometry for the Local
Group dwarf galaxies would help to establish an empirical connection
between these GCs and the primordial building blocks in the
hierarchical merging paradigm of galaxy formation.
Description:
Our observations in Ca, b, and y passbands were performed using the
Suprime-Cam on the Subaru telescope on the nights of 2012 December 8,
15, and 16. Only the images taken on the photometric condition (mostly
from the first night), with the seeing of 0.9"-1.2", were used. The
total exposure times for Ca, b, and y filters were 14940, 1908, and
954s, respectively, split into short and long exposures in each band.
Objects:
-----------------------------------------------
RA (ICRS) DE Designation(s)
-----------------------------------------------
07 38 08.51 +38 52 54.9 NGC 2419 = GCl 12
-----------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
fig1c.dat 17 1001 New Yonsei Ca filter transmission employed at
Subaru (figure 1c)
--------------------------------------------------------------------------------
See also:
B/subaru : Log of Subaru Prime Focus Camera Exposures (ADAC NAOJ, 2007)
J/MNRAS/431/1995 : Deep uVI photometry of NGC2419 (Beccari+, 2013)
J/ApJ/769/40 : Potassium abundance in red giants of GCs (Carretta+, 2013)
J/ApJ/760/86 : Equivalent widths for 13 NGC2419 RGB stars (Cohen+, 2012)
J/A+A/541/A15 : Abundances of M22 subgiants (Marino+, 2012)
J/ApJ/705/1481 : Spectroscopy of stars in 6 globular clusters (Da Costa+, 2009)
J/ApJ/681/311 : Blue stragglers in NGC 2419 (Dalessandro+, 2008)
J/AJ/131/461 : Stromgren photometry of NGC 2420 (Anthony-Twarog+, 2006)
Byte-by-byte Description of file: fig1c.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 0.1nm lambda Wavelength in Angstroms (1)
6- 17 F12.9 % Trans Transmission percentage (1)
--------------------------------------------------------------------------------
Note (1): Filter transmission function of new Yonsei Ca filter at
the prime focus focal plane (f/1.86) of Subaru Suprime-Cam
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 28-Apr-2015