J/ApJ/904/156 Classification of SNe in SDSS-II SNe Survey (Perrefort+, 2020)
A Template-based Approach to the Photometric Classification of SN1991bg-like
Supernovae in the SDSS-II Supernova Survey.
Perrefort D., Zhang Y., Galbany L., Wood-Vasey W.M., Gonzalez-Gaitan S.
<Astrophys. J., 904, 156 (2020)>
=2020ApJ...904..156P 2020ApJ...904..156P
ADC_Keywords: Supernovae; Photometry, ugriz; Redshifts
Keywords: Observational astronomy ; Supernovae ; Light curve
classification ; Type Ia supernovae
Abstract:
The use of SNe Ia to measure cosmological parameters has grown
significantly over the past two decades. However, there exists a
significant diversity in the SN Ia population that is not well
understood. Overluminous SN1991T-like and subluminous SN1991bg-like
objects are two characteristic examples of peculiar SNe. The
identification and classification of such objects is an important step
in studying what makes them unique from the remaining SN population.
With the upcoming Vera C. Rubin Observatory promising on the order of
a million new SNe over a 10 year survey, spectroscopic classifications
will be possible for only a small subset of observed targets. As such,
photometric classification has become an increasingly important
concern in preparing for the next generation of astronomical surveys.
Using observations from the Sloan Digital Sky Survey II (SDSS-II) SN
Survey, we apply here an empirically based classification technique
targeted at the identification of SN1991bg-like SNe in photometric
data sets. By performing dedicated fits to photometric data in the
rest-frame redder and bluer bandpasses, we classify 16 previously
unidentified 91bg-like SNe. Using SDSS-II host galaxy measurements, we
find that these SNe are preferentially found in host galaxies with an
older average stellar age than the hosts of normal SNe Ia. We also
find that these SNe are found at a further physical distance from the
center of their host galaxies. We find no statistically significant
bias in host galaxy mass or specific star formation rate for these
targets.
Description:
The SDSS II SN survey Sako+, 2018, II/333 (S18 hereafter) was
performed using the 2.5m Sloan Foundation Telescope at Apache Point
Observatory (APO). The SDSS II SN survey ran over three observing
seasons from 2005 to 2007, covering a 300 square degree stripe of sky
along the celestial equator in the Southern Galactic hemisphere in the
ugriz bands. All SDSS SNe are referred to in this work using their
associated Candidate Identifier (CID) published in S18.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 15 10 Objects identified in the SDSS SN Survey as being
potentially peculiar objects
table2.dat 99 89609 Fitted parameters listed for combination of models
and band-pass collections
table3.dat 89 6127 Parameters listed for fit results of the Salt 2.4
model to SDSS SNe.
table4.dat 32 16 *Classification coordinates
table5.dat 38 37 Comparison of objects classified as anomalies
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Note on table4.dat : Classification coordinates for objects classified
as being photometrically similar to SN1991bg. Included are coordinates
calculated by fitting photometric bandpasses independently (xBand,
yBand) and as collective red/blue sets (xCollective, yCollective). SNe
are classified as being 91bg-like if they satisfy xCollective x>3 and
yCollective >0. Missing (null) entries indicate a set of fits where
one or more fits failed to converge.
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See also:
II/333 : Sloan Digital Sky Survey-II Supernova Survey (Sako+, 2018)
J/AJ/134/973 : SDSS Stripe 82 star catalogs (Ivezic+, 2007)
J/AJ/136/2306 : SDSS-II Supernova survey, 2005 (Holtzman+, 2008)
J/AJ/135/348 : SDSS-II SNe survey: search and follow-up (Sako+, 2008)
J/AJ/135/1766 : Sloan Digital Sky Survey-II supernova survey (Zheng+, 2008)
J/AJ/137/4517 : UVOT light curves of supernovae (Brown+, 2009)
J/AJ/139/519 : Carnegie supernova project. SNe Ia (Contreras+, 2010)
J/ApJS/190/418 : Light curves for 165 SNe (Ganeshalingam+, 2010)
J/MNRAS/412/1441 : SNe luminosity functions (Li+, 2011)
J/ApJ/738/162 : SN Ia candidates from the SDSS-II SN Survey (Sako+, 2011)
J/AJ/142/156 : The CSP (DR2): photometry of SNe Ia (Stritzinger+, 2011)
J/ApJ/755/125 : Sample of SNe Ia with z<0.25 from SDSS (Galbany+, 2012)
J/AJ/144/17 : SDSS and CSP ugri photo. 9 type Ia supernova (Mosher+, 2012)
J/ApJS/203/32 : Machine-learned ASAS Classification Cat. (Richards+, 2012)
J/MNRAS/425/1789 : Berkeley supernova Ia program. I. (Silverman+, 2012)
J/A+A/552/A124 : SNLS-SDSS SN surveys photometric calibration (Betoule+, 2013)
J/ApJ/773/53 : Type Ia SNe spectroscopy by the CSP (Folatelli+, 2013)
J/A+A/568/A22 : Joint analysis of the SDSS-II and SNLS SNe Ia (Betoule+, 2014)
J/ApJ/795/142 : Defining photometric peculiar SNe Ia (Gonzalez-Gaitan+, 2014)
J/ApJ/795/44 : PS1 SNe Ia (0.02<z<0.7) griz light curves (Rest+, 2014)
J/AJ/151/33 : UBVRIz light curves of 51 Type II supernovae (Galbany+, 2016)
J/AJ/154/211 : The CSP (DR3): photometry of low-z SNe Ia (Krisciunas+, 2017)
J/AJ/156/18 : APOGEE DR14:Binary comp. evolved stars (Price-Whelan+, 2018)
J/ApJ/859/101 : The supernovae Ia Pantheon sample (Scolnic+, 2018)
J/A+A/630/A76 : SN2016hnk photometry and spectroscopy (Galbany+, 2019)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- CID [4524/20208] Object Identifier, Sako+, 2018, II/333
7- 15 A9 --- Class Similar supernovae classification
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- CID [679/22284] Object Identifier, Sako+, 2018, II/333
7- 10 A4 --- band Fitting band (1)
12- 17 A6 --- model Model fit (2)
19- 23 F5.3 --- z [0/0.99]? Redshift (3)
25- 29 F5.3 --- e_z [0/0.4]? Uncertainty in z (3)
31- 38 F8.2 d t0 [53606/54444]? time of B-band maximum, MJD
40- 44 F5.2 d e_t0 [0/20]? Uncertainty in t0
46- 49 F4.2 --- c [0/1]? color parameter (4)
51- 54 F4.2 --- e_c [0/1]? Uncertainty in c
56- 60 F5.2 --- x1 [-0.5/1.25]? stretch parameter (5)
62- 65 F4.2 --- e_x1 [0/1]? Uncertainty in x1
67- 70 F4.2 mag E(B-V) [0.01/0.36]? Milky Way extinction (6)
72- 81 F10.2 --- chisq [0.0/1732708.82]? Reduced χ^2
83- 87 F5.1 --- ndof [-2.0/240.0]? Number, degrees of freedom
89- 94 F6.2 mag Bmax [-35.97/43.23]? B-band maximum magnitude
96- 99 F4.2 mag DMB15 [0.52/2.49]? Light-curve parameter stretch
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Note (1): Bands as follows:
red = rest-frame effective wavelength >5500Angstroms;
blue = rest-frame effective wavelength <5500Angstroms;
ugirz = fits on a per SDSS CCD+filter basis;
all = fits to all bandpasses.
Note (2): Models as follows:
Hsiao = Spectral time-series template from Hsiao+, 2007ApJ...663.1187H 2007ApJ...663.1187H
sn91bg = SN 1991bg light-curve model
Note (3): Any redshift values missing a reported error were specified using
spectroscopic measurements.
Note (4): We note that the version of the Hsiao model used does not include
a color parameter c and thus has one degree of freedom more than the SN
1991bg model.
Note (5): Stretch-like parameter uniquely dependent on the model being
discussed. for Hsiao (H07) template x1 defined as in Equation 5; model
for 91bg-like SNe, we employ the same spectroscopic template used in the
PLAsTiCC challenge (The PLAsTiCC team+, 2018arXiv181000001T 2018arXiv181000001T)
Note (6): Milky Way extinction is determined using the Schlegel+,
1998ApJ...500..525S 1998ApJ...500..525S dust map and the Fitzpatrick, 1999PASP..111...63F 1999PASP..111...63F
extinction law. This value is never varied in any fit.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- CID [679/22284] Object Identifier, Sako+, 2018, II/333
7- 11 F5.3 --- z [0/2.16]? Redshift (1)
13- 17 F5.3 --- e_z [0/0.9]? Uncertainty in z (1)
19- 26 F8.2 d t0 [53606/54444]? time of B-band maximum, MJD
28- 32 F5.2 d e_t0 [0/20]? Uncertainty in t0
34- 38 F5.2 --- c [-0.5/0.5]? color parameter (1)
40- 43 F4.2 --- e_c [0/1]? Uncertainty in c
45- 49 F5.2 --- x1 [-5/5]? stretch parameter (1)
51- 55 F5.2 --- e_x1 [0/10]? Uncertainty in x1
57- 60 F4.2 mag E(B-V) [0.01/0.36]? Milky Way extinction (2)
62- 71 F10.2 --- chisq [7.78/6209152]? Reduced χ^2
73- 77 F5.1 --- ndof [8/230]? Number, degrees of freedom
79- 84 F6.2 mag Bmax [-25.99/21.02]? B-band maximum magnitude
86- 89 F4.2 mag DMB15 [0.17/3.26]? Light-curve parameter stretch
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Note (1): Any redshift values missing a reported error were specified using
spectroscopic measurements. For each fit the stretch parameter x1 was
bounded to the interval [-5,5] and the color parameter c to the
interval [-0.5,0.5]. If a spectroscopic redshift was not available, the
redshift was bounded to [0,1] and fit for.
Note (2): Milky Way extinction is determined using the Schlegel+,
1998ApJ...500..525S 1998ApJ...500..525S dust map and the Fitzpatrick, 1999PASP..111...63F 1999PASP..111...63F
extinction law. This value is never varied in any fit.
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Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 I5 --- CID [2778/21898] Object Identifier, Sako+, 2018, II/333
7- 12 F6.2 --- xBand [-20/12.3]? Photometric bandpass similarity SN91gb
14- 19 F6.2 --- yBand [-33.3/15.9]? Photometric bandpass similarity SN91gb
21- 25 F5.2 --- xColl [3.25/33.7] collective red/blue set similarity SN91gb
27- 32 F6.2 --- yColl [0.2/138] collective red/blue set similarity to SN91gb
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 I5 --- CID [1706/20266] Object Identifier, Sako+, 2018, II/33A
7- 13 A7 --- PSNID Candidate PSNID type, Sako+, 2018, II/333
15- 15 I1 --- Ndata [1/8] Number of datasets
17- 22 F6.2 --- x [-47.91/2.16] similarity coordinate
24- 29 F6.2 --- y [-27.26/0.97] similarity coordinate
31- 38 A8 --- Class Class (1)
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Note (1): Objects with coordinates x>3.00, y>0.00 are classified as SN
1991bg-like SNe. Objects with coordinates x<3.00, y<0.00 are
classified as normal, and objects with x<3.00, y>0.00 as peculiar.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie Fix [CDS], 16-Mar-2022