J/ApJ/960/49 HST survey of the young stellar cluster NGC2024 (Robberto+, 2024)
An HST study of the substellar population of NGC 2024.
Robberto M., Gennaro M., Da Rio N., Strampelli G.M., Ubeda L., Sabbi E.,
Koeppe D., Tan J.C., Soderblom D.R.
<Astrophys. J., 960, 49 (2024)>
=2024ApJ...960...49R 2024ApJ...960...49R
ADC_Keywords: Clusters, open; Photometry, HST; Infrared sources; Stars, masses;
Extinction; YSOs
Keywords: Young massive clusters ; Pre-main sequence stars ; Star formation
Abstract:
We performed an HST/WFC3-IR imaging survey of the young stellar
cluster NGC 2024 in three filters probing the 1.4µm H2O absorption
feature, characteristic of the population of low-mass and
substellar-mass objects down to a few Jupiter masses. We detect
812 point sources, 550 of them in all three filters with
signal-to-noise ratio greater than 5. Using a distance-independent
two-color diagram, we determine extinction values as high as AV∼40.
We also find that the change of effective wavelengths in our filters
results in higher AV values as the reddening increases. Reconstructing
a dereddened color-magnitude diagram, we derive a luminosity histogram
both for the full sample of candidate cluster members and for an
extinction-limited subsample containing the 50% of sources with
AV≲15. Assuming a standard extinction law like
Cardelli+ 1989ApJ...345..245C 1989ApJ...345..245C with a nominal RV=3.1, we produce a
luminosity function in good agreement with the one resulting from a
Salpeter-like initial mass function for a 1 Myr isochrone. There is
some evidence of an excess of luminous stars in the most embedded
region. We posit that the correlation may be due to those sources
being younger, and therefore overluminous, than the more evolved and
less extincted cluster's stars. We compare our classification scheme
based on the depth of the 1.4µm photometric feature with the
results from the spectroscopic survey of Levine+ 2006, J/ApJ/646/1215,
and we report a few peculiar sources and morphological features
typical of the rich phenomenology commonly encountered in young
star-forming regions.
Description:
The observations presented here are part of the HST GO-15334 program
(Principal Investigator Da Rio N.). They have been executed with the
Wide Field Camera 3 (WFC3) on board the HST between 2018 October and
2020 April. Twenty orbits were allocated to produce a mosaic of 5x4
WFC3/IR pointings, as shown in Figure 1.
Overall, the survey extends over 84.57 square arcminutes centered on
NGC 2024 coordinates (RAJ2000=05:41:42.945,DEJ2000=-01:54:18.58).
The filters used were F130N, F139M, and F105W.
We present the results obtained by performing aperture photometry on
the final drizzled images, with an extraction aperture of 0.4" and the
most recent (year 2020) release of the WFC3-IR zero-points. the
magnitudes were corrected to Vega magnitudes using the following
zero-points: ZP(130N)=21.797, ZP(F139M)=23.175, and ZP(F105W)=25.432.
The full photometric catalog, containing 812 entries, is presented in
Table 2.
In Table 3 we present the extinction and mass values estimated for the
candidate cluster members using the Cardelli+ 1989ApJ...345..245C 1989ApJ...345..245C law.
See Section 3.3.
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
05 41 42.94 -01 54 18.5 NGC 2024 = NGC 2024
----------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 65 812 WFC3-IR photometry from the HST GO-15334 program
table3.dat 15 397 Extinction and mass of candidate cluster members
--------------------------------------------------------------------------------
See also:
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
J/AJ/126/1665 : NICMOS observations of NGC 2024 (Liu+, 2003)
J/ApJ/598/375 : Chandra X-ray observations of NGC 2024 (Skinner+, 2003)
J/ApJ/646/1215 : Low-mass stars and brown dwarfs in NGC 2024 (Levine+, 2006)
J/ApJS/173/104 : Stellar population in Chamaeleon I (Luhman, 2007)
J/A+A/536/A63 : Collinder 69 very low mass stars and BDs (Bayo+, 2011)
J/ApJ/754/30 : VISTA IR phot. of σ Ori cluster (Pena Ramirez+, 2012)
J/MNRAS/431/3222 : UKIDSS GCS Upper Sco members (Lodieu, 2013)
J/MNRAS/444/1793 : 25 Ori group low-mass stars (Downes+, 2014)
J/ApJ/787/109 : Age estimates for NGC 2024 and ONC stars (Getman+, 2014
J/MNRAS/463/2653 : 8620 DIB equivalent width and extinction (Damineli+, 2016)
J/MNRAS/486/1718 : System IMF of 25 Ori (Suarez+, 2019)
J/ApJ/896/79 : HST survey of ONC in H20 1.4um abs. I. (Robberto+, 2020)
J/A+A/640/A27 : Protoplanetary disk masses in NGC 2024 (van Terwisga+, 2020)
J/A+A/666/A113 : Stellar integrated gal. initial mass function (Dib, 2022)
J/A+A/677/A26 : (sub)stellar members of NGC 2244 sp. (Almendros-Abad+, 2023)
J/ApJ/951/139 : W filter YSOs detection. VI. sigma Orionis (Damian+, 2023)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Seq [1/812] Sequential identifier
5- 13 F9.6 deg RAdeg [85.3/85.6] Right Ascension (J2000)
15- 23 F9.6 deg DEdeg [-2.1/-1.8] Declination (J2000)
25- 30 F6.3 mag F105Wmag [12.43/29.3]?=99.999 HST/WFC3 F105W filter
magnitude (Vega mag) (1)
32- 37 F6.3 mag e_F105Wmag [0/1.4]?=99.999 F105Wmag uncertainty (1)
39- 44 F6.3 mag F130Nmag [9.98/25.9]?=99.999 HST/WFC3 F130N filter
magnitude (Vega mag) (1)
46- 51 F6.3 mag e_F130Nmag [0/0.4]?=99.999 F130Nmag uncertainty (1)
53- 58 F6.3 mag F139Mmag [9.89/23.2]?=99.999 HST/WFC3 F139M filter
magnitude (Vega mag) (1)
60- 65 F6.3 mag e_F139Mmag [0/0.4]?=99.999 F139Mmag uncertainty (1)
--------------------------------------------------------------------------------
Note (1): When a value is given for a magnitude but the error is set to null
(99.999) then the magnitude is a 3σ upper limit.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Seq [1/809] Sequential identifier
5- 9 F5.2 mag Av [-5.25/42.9]? Visual extinction (1)
11- 15 F5.3 Msun Mstar [0.003/1.4]? Stellar mass
--------------------------------------------------------------------------------
Note (1): Negative extinctions are derived for a few sources in the
Color-Color Diagram that lie below the corresponding isochrone. The
anomaly may be due to measurement uncertainty, or to some sort of
bluish excess possibility accretion, that is not accounted for by
the bare photosphere isochrone. The mass estimates are consistent
with the (slightly) anomalous position of the star in the
Color-Magnitude diagram.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 06-Mar-2026