J/MNRAS/508/3388 Cygnus OB2 Complex survey with Subaru HSC (Gupta+, 2021)
Subaru Hyper Suprime-Cam Survey of Cygnus OB2 Complex.
I. Introduction, photometry, and source catalogue.
Gupta S., Jose J., More S., Das S.R., Herczeg G.J., Samal M.R., Guo Z.,
Prakash P., Damian B., Takami M., Takahashi S., Ogura K., Terai T.,
Pyo T.-S.
<Mon. Not. R. Astron. Soc. 508, 3388-3407 (2021)>
=2021MNRAS.508.3388G 2021MNRAS.508.3388G (SIMBAD/NED BibCode)
ADC_Keywords: Associations, stellar ; Clusters, open ; Stars, OB ;
Star Forming Region ; Positional data ; Optical ; Infrared ;
Photometry
Keywords: methods: observational - techniques: photometric - catalogues -
stars: imaging - stars: low-mass - stars: pre-main-sequence
Abstract:
Low-mass star formation inside massive clusters is crucial to
understand the effect of cluster environment on processes like
circumstellar disc evolution, planet, and brown dwarf formation. The
young massive association of Cygnus OB2, with a strong feedback from
massive stars, is an ideal target to study the effect of extreme
environmental conditions on its extensive low-mass population. We aim
to perform deep multiwavelength studies to understand the role of
stellar feedback on the IMF, brown dwarf fraction and circumstellar
disc properties in the region. We introduce here, the deepest and
widest optical photometry of 1.5° diameter region centred at
Cygnus OB2 in r2, i2, z, and Y-filters, using Subaru Hyper
Suprime-Cam (HSC). This work presents the data reduction, source
catalogue generation, data quality checks, and preliminary results
about the pre-main sequence sources. We obtain 713529 sources in
total, with detection down to ∼28, 27, 25.5, and 24.5 mag in r2,
i2, z, and Y-band, respectively, which is ∼ 3 - 5 mag deeper than
the existing Pan-STARRS and GTC/OSIRIS photometry. We confirm the
presence of a distinct pre-main sequence branch by statistical field
subtraction of the central 18 arcmin region. We find the median age of
the region as ∼5 ± 2 Myr with an average disc fraction of ∼9 per
cent. At this age, combined with AV ∼ 6 - 8 mag, we detect sources
down to a mass range of ∼0.01-0.17 M☉. The deep HSC catalogue
will serve as the groundwork for further studies on this prominent
active young cluster.
Description:
Cygnus OB2 (RA: 20:33:15, Dec.: +41:18:54), located at ∼ 1.6 kpc (Lim
et al. 2019MNRAS.490..440L 2019MNRAS.490..440L, Cat. J/MNRAS/490/440) from the Sun, is a
typical analogue of the extragalactic massive star-forming regions
located outside the solar neighbourhood. It is the central massive
OB-association 2-10 * 104 M_☉ as determined by Knodlseder
(2000A&A...360..539K 2000A&A...360..539K), Wright et al. (2010ApJ...713..871W 2010ApJ...713..871W,
Cat. J/ApJ/713/871) embedded in the giant Cygnus X molecular complex
(Schneider et al. 2006A&A...458..855S 2006A&A...458..855S; Reipurth & Schneider
2008hsf1.book...36R 2008hsf1.book...36R) and harbours ∼ 220 OB-type stars (Comeron &
Pasquali 2012A&A...543A.101C 2012A&A...543A.101C, Cat. J/A+A/543/A101; Berlanas et al.
2020A&A...642A.168B 2020A&A...642A.168B, Cat. J/A+A/642/A168) along with tens of thousands
of low-mass stars (Albacete Colombo et al. 2007A&A...464..211A 2007A&A...464..211A,
Cat. J/A+A/464/211; Drew et al. 2008MNRAS.386.1761D 2008MNRAS.386.1761D; Wright & Drake
2009ApJS..184...84W 2009ApJS..184...84W, Cat. J/ApJS/184/84). The OB2 association has an
estimated age of ∼3-5 Myr (Drew et al. 2008MNRAS.386.1761D 2008MNRAS.386.1761D, Wright et
al. 2010ApJ...713..871W 2010ApJ...713..871W, Cat. J/ApJ/713/871; Wright et al.
2015MNRAS.449..741W 2015MNRAS.449..741W, Cat. J/MNRAS/449/741) and is affected by variable
extinction, AV anging between ∼ 4 and 8 mag (Wright et al.
2015MNRAS.449..741W 2015MNRAS.449..741W, Cat. J/MNRAS/449/741). With a cluster environment
impinged by high-energy radiation from massive OB-stars in the
association, Cygnus OB2 is an ideal laboratory to study the role of
stellar feedback on the surrounding low-mass stellar population in the
region, (i.e section 1 introduction).
We observe Cygnus OB2 with the Subaru 8.2 m class optical-infrared
telescope built and operated by the National Astronomical Observatory
of Japan (NAOJ). With an 870 Megapixels mosaic CCD camera comprising
of 116 2k * 4k CCDs with a pixel scale ∼0.17 arcsec, the Hyper
Suprime-Cam (HSC) instrument installed at the prime focus of the
telescope provides an excellent image quality over a wide field of
view. We observed a region of 1.5 degree diameter centred at Cygnus
OB2 in four broad-band optical filters, namely r2,i2,z and Y
(Kawanomoto et al. 2018PASJ...70...66K 2018PASJ...70...66K), (i.e section 2.1 HSC Observations).
As explained in the section 2.2 Data reduction and catalog generation,
the observed raw data were downloaded from STARS (Subaru Telescope
Archive System) and reduced with the help of HSC Pipeline version 6.7.
We apply certain flags and external constraints to remove the spurious
contamination from the obtained long and short-exposure catalogues with
minimal loss of genuine point sources in individual filters.
To summarize, the output catalogue thus procured, includes only those
sources which have detection in at least any two filters, photometric
error =< 0.1 mag in all the filters and internal astrometric
uncertainty =< 0.1 arcsec. We have finally secured 713529 point
sources all of which have at least a two-band detection.
Approximately, 699798 (∼98 per cent) sources have Y-band photometry,
685511 sources (∼ 96 per cent) have z-band photometry, 622011 sources
(∼90 per cent) have i2 band photometry and 358 372 sources (∼ 50 per
cent) have r2 band photometry, (i.e section 2.3 Point source
selection). Results are presented in the table4.dat.
Further in this study (i.e section 3 data quality), we proceed to data
quality checking in terms of the photometry, astrometry, limiting
magnitude of detection, completeness of the reduced HSC data with
respect to the existing Pan-STARRS DR1 (Chambers et al.
2016arXiv161205560C 2016arXiv161205560C, Cat. II/349) and GTC/OSIRIS (Guarcello et al.
2012ApJS..202...19G 2012ApJS..202...19G, Cat. J/ApJS/202/19) optical data. We also perform
a comparison of the obtained HSC photometry with respect to Pan-STARRS
DR1 photometry with the help of magnitude offset plots and check the
astrometric offset with respect to Pan-STARRS DR1 and Gaia EDR3 data
(Brown et al. 2016A&A...595A...2G 2016A&A...595A...2G, Gaia Collaboration
2021A&A...649A...1G 2021A&A...649A...1G, Cat. I/350).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table4.dat 76 713529 *Sample table of HSC catalogue data
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Note on table4.dat: Subaru HSC in four broad-band optical filters, namely r2,
i2, z and Y (Kawanomoto et al. 2018PASJ...70...66K 2018PASJ...70...66K) on 2017 on 2017 September
17 (PI: J. Jose; Program ID: S17B0108N), using EAO (East Asian Observatory)
time. See (https://hsc-release.mtk.nao.ac.jp/doc/index.php/survey/) to get
filters profiles.
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See also:
J/MNRAS/490/440 : Gaia view of Cygnus OB2 and Carina OB1 associations
(Lim+, 2019)
J/ApJ/713/871 : Sources in star-forming region Cyg-OB2 from X-ray
(Wright+, 2010)
J/A+A/543/A101 : OB stars in Cygnus OB2 association (Comeron+, 2012)
J/A+A/642/A168 : Cygnus OB2 O stars spectroscopic analysis (Berlanas+, 2020)
J/A+A/464/211 : Chandra and near-IR obs. of Cyg OB2 (Albacete Colombo+, 2007)
J/ApJS/184/84 : X-ray sources in Cyg OB2 region (Wright+, 2009)
J/MNRAS/449/741 : The massive star population of Cygnus OB2 (Wright+, 2015)
II/349 : The Pan-STARRS release 1 (PS1) Survey - DR1 (Chambers+, 2016)
J/ApJS/202/19 : riz photometry in Cyg OB2 (Guarcello+, 2012)
I/350 : Gaia EDR3 (Gaia Collaboration, 2020)
Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 10 F10.6 deg RAdeg Right ascension (J2000) (RA)
12- 20 F9.6 deg DEdeg Declination (J2000) (Dec)
22- 27 F6.3 mag r2mag ?=- Apparent magnitude in subaru HSC
broad-band optical filter r2 (r2)
29- 34 F6.3 mag e_r2mag ?=- Mean error on r2mag (r2_err)
36- 41 F6.3 mag i2mag ?=- Apparent magnitude in subaru HSC
broad-band optical filter i2 (i2)
43- 48 F6.3 mag e_i2mag ?=- Mean error on i2mag (i2err)
50- 55 F6.3 mag zmag ?=- Apparent magnitude in subaru HSC
broad-band near infrared filter z (z)
57- 62 F6.3 mag e_zmag ?=- Mean error on zmag (z_err)
64- 69 F6.3 mag Ymag ?=- Apparent magnitude in subaru HSC
broad-band near infrared filter Y (Y)
71- 76 F6.3 mag e_Ymag ?=- Mean error on Y (Y_err)
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History:
From electronic version of the journal
(End) Luc Trabelsi [CDS] 13-Aug-2024