J/A+A/695/A264 ZTF SN Ia DR2. SiII6355 high-velocity comp. (Harvey+, 2025)
ZTF SN Ia DR2: High-velocity components in the Si II λ6355.
Harvey L., Maguire K., Burgaz U., Dimitriadis G., Sollerman J., Goobar A.,
Johansson J., Nordin J., Rigault M., Smith M., Aubert M., Cartier R.,
Chen P., Deckers M., Dhawan S., Galbany L., Ginolin M., Kenworthy W.D.,
Kim Y.-L., Liu C., Miller A., Rosnet P., Senzel R., Terwel J.H.,
Tomasella L., Kasliwal M., Laher R.R., Purdum J., Rusholme B., Smith R.
<Astron. Astrophys. 695, A264 (2025)>
=2025A&A...695A.264H 2025A&A...695A.264H (SIMBAD/NED BibCode)
ADC_Keywords: Supernovae ; Spectroscopy
Keywords: techniques: spectroscopic - supernovae: general
Abstract:
The Zwicky Transient Facility SN Ia Data Release 2 provides a perfect
opportunity to perform a thorough search for, and subsequent
analysis of, high-velocity components in the SiII λ6355 feature
in the pre-peak regime. The source of such features remains unclear,
with potential origins in circumstellar material or density/abundance
enhancements intrinsic to the SN ejecta. Therefore, they may provide
clues to the elusive progenitor and explosion scenarios of SNe Ia. We
employ a Markov-Chain Monte Carlo fitting method followed by Bayesian
Information Criterion testing to classify single and double SiII
λ6355 components in the DR2. The detection efficiency of our
classification method is investigated through the fitting of simulated
features, allowing us to place cuts upon spectral quality required for
reliable classification. These simulations were also used to perform
an analysis of the recovered parameter uncertainties and potential
biases in the measurements.Within the 329 spectra sample that we
investigate, we identify 85 spectra exhibiting SiII λ6355 HVFs.
We find that HVFs decrease in strength with phase relative to their
photospheric counterparts - however, this decrease can occur at
different phases for different objects. HVFs with larger velocity
separations from the photosphere are seen to fade earlier leaving only
the double components with smaller separations as we move towards
maximum light. Our findings suggest that around three quarters of SN
Ia spectra before ∼11d show high-velocity components in the SiII
λ6355 with this dropping to around one third in the six days
before maximum light. We observe no difference between the populations
of SNe Ia that do and do not form SiII λ6355 HVFs in terms of
SALT2 light-curve parameter x1, peak magnitude, decline rate, host
mass, or host colour, supporting the idea that these features are
ubiquitous across the SN Ia population.
Description:
Parameter measurements from the MCMC fitting of the 329 spectra in the
final sample. 244 of the spectra were identified to not possess a HVF
and are therefore presented in pvf.dat with the measurements from the
one-component model (Equation 1). The remaining 85 spectra were
identified to exhibit a HVF, the parameters measurements for these
spectra from the two-component model (Equation 2) are presented in
hvf.dat.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
pvf.dat 149 244 Measurements of the 244 spectra not containing
a HV feature in the SiII 6355 (table B1)
hvf.dat 253 85 Measurements of the 85 spectra containing a
HV feature in the SiII 6355 (table B2)
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See also:
J/A+A/694/A9 : Spectral Measurements of ZTF SN Ia DR2 (Burgaz+, 2025)
J/A+A/694/A10 : ZTF SN Ia DR2 (Dimitriadis+, 2025)
J/A+A/694/A11 : SN 2020alm spectrum (Terwel+, 2025)
J/A+A/694/A12 : ZTF SN Ia DR2. secondary maximum in Type Ia SN (Deckers+, 2025)
Byte-by-byte Description of file: pvf.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 A12 --- ZTF Internal name within ZTF (ztf_name)
14- 21 A8 --- Name IAU designated name (iau_name)
23- 32 F10.6 deg RAdeg Right ascension (J2000)
34- 43 F10.6 deg DEdeg Declination (J2000)
45- 51 F7.1 d MJD Modified Julian Date of spectrum (mjd)
53- 57 F5.1 d Phase Phase of spectrum relative to date of
maximum light (phase)
59- 61 F3.1 d e_Phase Uncertainty of phase (phase_err)
63- 67 F5.3 --- aPV Depth of PV component (a_pv) (G1)
69- 73 F5.3 --- e_aPV Lower uncertainty of depth of PV component
(apverr_low)
75- 79 F5.3 --- E_aPV Upper uncertainty of depth of PV component
(apverr_upp)
81- 86 F6.1 0.1nm bPV Centroid of PV component (b_pv) (G1)
88- 90 F3.1 0.1nm e_bPV Lower uncertainty of centroid of PV component
(bpverr_low)
92- 94 F3.1 0.1nm E_bPV Upper uncertainty of centroid of PV component
(bpverr_upp)
96-100 F5.1 0.1nm cPV Width of PV component (c_pv) (G1)
102-105 F4.1 0.1nm e_cPV Lower uncertainty of width of PV component
(cpverr_low)
107-110 F4.1 0.1nm E_cPV Upper uncertainty of width of PV component
(cpverr_upp)
112-116 F5.1 0.1nm pewPV Pseudo equivalent width of PV component
(pew_pv)
118-121 F4.1 0.1nm e_pewPV Lower uncertainty of pseudo equivalent width
of PV component (pewpverr_low)
123-126 F4.1 0.1nm E_pewPV Upper uncertainty of pseudo equivalent width
of PV component (pewpverr_upp)
128-141 A14 --- Tel Source telescope for spectrum (telescope)
143-149 A7 --- Inst Source spectrograph for spectrum (instrument)
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Byte-by-byte Description of file: hvf.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 A12 --- ZTF Internal name within ZTF (ztf_name)
14- 21 A8 --- Name IAU designated name (iau_name)
23- 32 F10.6 deg RAdeg Right ascension (J2000)
34- 43 F10.6 deg DEdeg Declination (J2000)
45- 51 F7.1 d MJD Modified Julian Date of spectrum (mjd)
53- 57 F5.1 d Phase Phase of spectrum relative to date of
maximum light (phase)
59- 61 F3.1 d e_Phase Uncertainty of phase (phase_err)
63- 67 F5.3 --- aPV Depth of PV component (a_pv) (G1)
69- 73 F5.3 --- e_aPV Lower uncertainty of depth of PV component
(apverr_low)
75- 79 F5.3 --- E_aPV Upper uncertainty of depth of PV component
(apverr_upp)
81- 86 F6.1 0.1nm bPV Centroid of PV component (b_pv) (G1)
88- 91 F4.1 0.1nm e_bPV Lower uncertainty of centroid of PV component
(bpverr_low)
93- 96 F4.1 0.1nm E_bPV Upper uncertainty of centroid of PV component
(bpverr_upp)
98-102 F5.1 0.1nm cPV Width of PV component (c_pv) (G1)
104-107 F4.1 0.1nm e_cPV Lower uncertainty of width of PV component
(cpverr_low)
109-112 F4.1 0.1nm E_cPV Upper uncertainty of width of PV component
(cpverr_upp)
114-118 F5.3 --- aHV Depth of HV component (a_hv) (G1)
120-124 F5.3 --- e_aHV Lower uncertainty of depth of HV component
(ahverr_low)
126-130 F5.3 --- E_aHV Upper uncertainty of depth of HV component
(ahverr_upp)
132-137 F6.1 0.1nm bHV Centroid of HV component (b_hv) (G1)
139-142 F4.1 0.1nm e_bHV Lower uncertainty of centroid of HV component
(bhverr_low)
144-147 F4.1 0.1nm E_bHV Upper uncertainty of centroid of HV component
(bhverr_upp)
149-152 F4.1 0.1nm cHV Width of HV component (c_hv) (G1)
154-157 F4.1 0.1nm e_cHV Lower uncertainty of width of HV component
(chverr_low)
159-162 F4.1 0.1nm E_cHV Upper uncertainty of width of HV component
(chverr_upp)
164-168 F5.1 0.1nm pewPV Pseudo equivalent width of PV component
(pew_pv)
170-173 F4.1 0.1nm e_pewPV Lower uncertainty of pseudo equivalent width
of PV component (pewpverr_low)
175-178 F4.1 0.1nm E_pewPV Upper uncertainty of pseudo equivalent width
of PV component (pewpverr_upp)
180-184 F5.1 0.1nm pewHV Pseudo equivalent width of HV component
(pew_hv)
186-189 F4.1 0.1nm e_pewHV Lower uncertainty of pseudo equivalent width
of HV component (pewhverr_low)
191-194 F4.1 0.1nm E_pewHV Upper uncertainty of pseudo equivalent width
of HV component (pewhverr_upp)
196-199 F4.2 --- R Ratio of pews (pewhv/pewpv) (R)
201-204 F4.2 --- e_R Lower uncertainty of pew ratio (Rerrlow)
206-209 F4.2 --- E_R Upper uncertainty of pew ratio (Rerrupp)
211-216 F6.1 km/s Vsep Velocity separation between the PV and HV
components (vsep)
218-223 F6.1 km/s e_Vsep Lower uncertainty of velocity separation
(vseperrlow)
225-230 F6.1 km/s E_Vsep Upper uncertainty of velocity separation
(vseperrupp)
232-245 A14 --- Tel Source telescope for spectrum (telescope)
247-253 A7 --- Inst Source spectrograph for spectrum (instrument)
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Global notes:
Note (G1): The single (f1) and double (f2) component models take the forms,
f1=(1-g(λ, aPV, bPV, cPV))(sλ+i) (1)
and
f2 =(1-g(λ, aPV, bPV, cPV)-g(λ, aHV, bHV, cHV))(sλ+i) (2)
with f as the flux, s and i as the continuum slope and intercept
respectively, and g(λ, a, b, c) being an individual SiII λ6355
doublet of the form:
a*exp[-(λ-(b-7.89))2/2c2]+a*exp[-(λ-(b+16.37))2/2c2] (3)
where a is the depth of one of the singlets, b is the wavelength position of
the minimum, with the 7.89 and 16.37 quantities as the offsets from 6355Å
for the 6347.11Å and 6371.37Å lines of the doublet, c is the width,
and the PV and HV subscripts refer to the photospheric- and high-velocity
components of the model, respectively.
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Acknowledgements:
Luke Harvey, luharvey(at)tcd.ie
(End) Patricia Vannier [CDS] 12-Feb-2025