Spectra of supernova 2017eaw in NGC 6946


SN 2017eaw is the first bright supernova this year (2017) in northern hemisphere. With maximum brightness of V=12.8 mag it is easy reachable whithin the Alpy600 spectrograph. This supernova has a large distance to the nucleus of its host galaxy, the nice spiral NGC 6946. Up to now I took eight spectra:
  1.   2017-05-21 in the early morning hours. The sky was clear with some cirrostratus.
  2.   2017-05-26 in the second half of the night. The sky was clear with a very good transparence.
  3.   2017-06-10 in the second half of the night. The sky was clear but with almost full moon.
  4.   2017-06-24 during midnight. The sky was clear with average conditions.
  5.   2017-07-08 during midnight. There was only a very short window of clear sky, the recording session was aborted after half an hour.
  6.   2017-07-16 in the early morning hours. Much patience was needed to wait for the sky clearing off, than I had good conditions.
  7.   2017-07-29 during midnight. The sky was clear with average conditions.
  8.   2017-08-27 in the early morning hours. Much patience was needed to wait for the sky clearing off, than I had good seeing but high humidity.
I recorded the spectra of SN 2017eaw when the object was in a comfortable altitude (more than 48°).

Data about supernova 2017eaw

Position: RA 20h34m44s.238, DEC +60°11'36".00
Location: 61".0 west, 143".0 north of the center of NGC 6946
Discovery: 2017-05-14.238 by Patrick Wiggins
Brightness:
2017-05-21   12.8 mag
2017-05-26   12.9 mag
2017-06-10   13.1 mag
2017-06-24   13.2 mag
2017-07-08   13.2 mag
2017-07-16   13.3 mag
2017-07-29   13.3 mag
2017-08-27   13.9 mag
see light curve of SN 2017eaw
Type of SN: IIP


Image and spectra of supernova 2017eaw

Image of supernova 2017eaw in NGC 6946
2017-05-25 21:53 - 22:49 UT, Roof Observatory Kaufering, Meade 14" ACF telescope on Taurus GM-60 mount, CCD: Moravian G2-8300FW, 3x3 binning, L-filter, exposure: 60x30s; magnitude measured with Astrometrica: 12.9 mag; see 2017eaw at latest Supernovae page

Additionally I'm going to show a screenshot of guiding camera during spectra recording:

Screenshot from guiding camera during spectra recording
The "star" in yellow circle is the supernova. It seems to be divided into two parts. The SN is positioned exaclty on entrance slit, its main part of light goes into the spectrograph and the remaining light is reflected into the guiding camera. The slit itself is invisible.


Here are my spectra of this supernova:

Spectrum of supernova 2017eaw 2017-05-21
2017-05-21 00:57 - 02:04 UT, Roof Observatory Kaufering, Meade 14" ACF telescope on Taurus GM-60 mount, Astro Physics reducer CCDT67, Alpy600 with guiding unit, CCD camera: Atik 428EX, guiding camera: ASI 120 MM; recording software: AstroArt, guiding software: PHD;
Wavelength calibration: Hg lines from energy saving lamp and Ne lines from flicker flame light bulbs, instrumental response calibration: with reference star 33 Cygni (HD 192696, A3 IV-Vn), data reduction: with Integrated Spectrographic Innovative Software from Christian Buil;
The spectrum has been cut at the near UV end (3800 Å) due to strong noise.


Spectrum of supernova 2017eaw 2017-05-26
2017-05-26 00:11 - 01:28 UT, Roof Observatory Kaufering, Meade 14" ACF telescope on Taurus GM-60 mount, Astro Physics reducer CCDT67, Alpy600 with guiding unit, CCD camera: Atik 428EX, guiding camera: ASI 120 MM; recording software: AstroArt, guiding software: PHD;
Wavelength calibration: Hg lines from energy saving lamp and Ne lines from flicker flame light bulbs, instrumental response calibration: with reference star 33 Cygni (HD 192696, A3 IV-Vn), data reduction: with Integrated Spectrographic Innovative Software;
The spectrum has been cut at the near UV end (3800 Å) due to strong noise.


Spectrum of supernova 2017eaw 2017-06-10
2017-06-10 22:53 - 00:37 UT, Roof Observatory Kaufering, Meade 14" ACF telescope on Taurus GM-60 mount, Astro Physics reducer CCDT67, Alpy600 with guiding unit, CCD camera: Atik 428EX, guiding camera: ASI 120 MM; recording software: AstroArt, guiding software: PHD;
Wavelength calibration: Hg lines from energy saving lamp and Ne lines from flicker flame light bulbs, instrumental response calibration: with reference star 33 Cygni (HD 192696, A3 IV-Vn), data reduction: with Integrated Spectrographic Innovative Software;
The spectrum has been cut at the near UV end (3770 Å) due to strong noise.


Spectrum of supernova 2017eaw 2017-06-24
2017-06-24 21:52 - 23:58 UT, Roof Observatory Kaufering, Meade 14" ACF telescope on Taurus GM-60 mount, Astro Physics reducer CCDT67, Alpy600 with guiding unit, CCD camera: Atik 428EX, guiding camera: ASI 120 MM; recording software: AstroArt, guiding software: PHD;
Wavelength calibration: Hg lines from energy saving lamp and Ne lines from flicker flame light bulbs, instrumental response calibration: with reference star 33 Cygni (HD 192696, A3 IV-Vn), data reduction: with Integrated Spectrographic Innovative Software;
The spectrum has been cut at the near UV end (3785 Å) due to strong noise.


Spectrum of supernova 2017eaw 2017-07-08
2017-07-08 22:38 - 23:07 UT, Roof Observatory Kaufering, Meade 14" ACF telescope on Taurus GM-60 mount, Astro Physics reducer CCDT67, Alpy600 with guiding unit, CCD camera: Atik 428EX, guiding camera: ASI 120 MM; recording software: AstroArt, guiding software: PHD;
Wavelength calibration: Hg lines from energy saving lamp and Ne lines from flicker flame light bulbs, instrumental response calibration: with reference star 33 Cygni (HD 192696, A3 IV-Vn) from last session, data reduction: with Integrated Spectrographic Innovative Software;
The spectrum has been cut at the near UV end (3770 Å) due to strong noise.


Spectrum of supernova 2017eaw 2017-07-16
2017-07-16 00:17 - 01:53 UT, Roof Observatory Kaufering, Meade 14" ACF telescope on Taurus GM-60 mount, Astro Physics reducer CCDT67, Alpy600 with guiding unit, CCD camera: Atik 428EX, guiding camera: ASI 120 MM; recording software: AstroArt, guiding software: PHD;
Wavelength calibration: Hg lines from energy saving lamp and Ne lines from flicker flame light bulbs, instrumental response calibration: with reference star 33 Cygni (HD 192696, A3 IV-Vn), data reduction: with Integrated Spectrographic Innovative Software;
The spectrum has been cut at the near UV end (3770 Å) due to strong noise.


Spectrum of supernova 2017eaw 2017-07-29
2017-07-29 21:03 - 23:08 UT, Roof Observatory Kaufering, Meade 14" ACF telescope on Taurus GM-60 mount, Astro Physics reducer CCDT67, Alpy600 with guiding unit, CCD camera: Atik 428EX, guiding camera: ASI 120 MM; recording software: AstroArt, guiding software: PHD;
Wavelength calibration: Hg lines from energy saving lamp and Ne lines from flicker flame light bulbs, instrumental response calibration: with reference star 33 Cygni (HD 192696, A3 IV-Vn), data reduction: with Integrated Spectrographic Innovative Software;
The spectrum has been cut at the near UV end (3770 Å) due to strong noise.


Spectrum of supernova 2017eaw 2017-08-27
2017-08-27 23:51 - 02:16 UT, Roof Observatory Kaufering, Meade 14" ACF telescope on Taurus GM-60 mount, Astro Physics reducer CCDT67, Alpy600 with guiding unit, CCD camera: Atik 428EX, guiding camera: ASI 120 MM; recording software: AstroArt, guiding software: PHD;
Wavelength calibration: Hg lines from energy saving lamp and Ne lines from flicker flame light bulbs, instrumental response calibration: with reference star 33 Cygni (HD 192696, A3 IV-Vn), data reduction: with Integrated Spectrographic Innovative Software;
The spectrum has been cut at the near UV end (3800 Å) due to strong noise.




Classification of supernova 2017eaw

The classification with two independent methods confirms the already known type IIP, see TNS page.

1) Classification with GELATO (Padova-Asiago Supernova Group), see [1].

Identification of supernova 2017eaw with GELATO

Identification of supernova 2017eaw 2017-05-21
Spectrum from 2017-05-21 best matches to SN 1992H (IIP) with age of 12.5 d (Quality factor: 1.99).

Identification of supernova 2017eaw 2017-05-26
Spectrum from 2017-05-26 best matches to SN 1992H (IIP) with age of 15.5 d (Quality factor: 2.17).

Identification of supernova 2017eaw 2017-06-10
Spectrum from 2017-06-10 third best matches to SN 1999gi (IIP) with age of 29.8 d (Quality factor: 4.36).

Identification of supernova 2017eaw 2017-06-24
Spectrum from 2017-06-24 best matches to SN 1999gi (IIP) with age of 37.8 d (Quality factor: 4.45).

Identification of supernova 2017eaw 2017-07-08
Spectrum from 2017-07-08 second best matches to SN 2004et (IIP) with age of 54.0 d (Quality factor: 3.13).

Identification of supernova 2017eaw 2017-07-16
Spectrum from 2017-07-16 second best matches to SN 2004et (IIP) with age of 50.6 d (Quality factor: 2.93).

Identification of supernova 2017eaw 2017-07-29
Spectrum from 2017-07-29 best matches to SN 2004et (IIP) with age of 73.6 d (Quality factor: 3.72).

Identification of supernova 2017eaw 2017-08-27
Spectrum from 2017-08-27 third best matches to SN 2004et (IIP) with age of 114.8 d (Quality factor: 2.33).


2) Classification with SNID (SuperNova IDentification), see [2].

Identification of supernova 2017eaw with SNID
Spectrum from 2017-05-21 best matches to SN 2006bp (IIP) with age of 0.1 d.

Identification of supernova 2017eaw with SNID
Spectrum from 2017-05-26 best matches to SN 2004et (IIP) with age of -2.9 d.

Identification of supernova 2017eaw with SNID
Spectrum from 2017-06-10 best matches to SN 2006bp (IIP) with age of 20.1 d.

Identification of supernova 2017eaw with SNID
Spectrum from 2017-06-24 third best matches to SN 2006bp (IIP) with age of 34.0 d.

Identification of supernova 2017eaw with SNID
Spectrum from 2017-07-08 second best matches to SN 2006bp (IIP) with age of 49.0 d.

Identification of supernova 2017eaw with SNID
Spectrum from 2017-07-16 fifth best matches to SN 2006bp (IIP) with age of 49.0 d.

Identification of supernova 2017eaw with SNID
Spectrum from 2017-07-29 best matches to SN 2006bp (IIP) with age of 65.0 d.

Identification of supernova 2017eaw with SNID
Spectrum from 2017-08-27 second best matches to SN 2004et (IIP) with age of 83.0 d.

The determination of age seems to be difficult, there are large differences between GELATO and SNID. In both tools the red shift (z=0.00015) of host galaxy has been entered.
Note: The age in GELATO is given in days since explosion, wheras the age in SNID is given in days since maximum brightness.



Line identification and discussion

The features in supernova spectra are all broad due to the very high ejection velocities, which typically are in excess of 10.000 km/s in young SN [3],[5]. According to ATEL #10377 the ejection velocity in SN 20117eaw is about 14300 km/s (at age -6 d) [4]. A prominent feature in early type IIP supernovae is a strong H-Alpha emission with a blue shifted absorption feature (P-Cygni profile). H-Beta and H-Gamma emission lines with blue shifted absorption features are also seen. He I emission with blue shifted absorption feature and Si II absorption are present [6]. A sharp line of Na I D from interstellar matter also appears. In spectra of older SN metal absorption lines of Fe, Ba, Ca, Ti, Sr and Sc are visible [7].


Labeled early spectrum:
Labeled spectrum of supernova 2017eaw in NGC 6946
PCP - P-Cygni profile


Labeled spectrum 21 d after maximum light:
Labeled spectrum of supernova 2017eaw in NGC 6946
I used a fit curve close to original to supress the noise. In the great paper from Bose et al., [7] is a spectrum with line identification of IIP SN 2013ab based on SYNOW modelling. I marked the lines in my spectrum accordingly, that could be clearly identified. Obviously the features have varying shifts. According to [7] the lines come from different layers or depths of expanding matter. The H-Alpha absorption has the largest shift, it must come from the fastest and outermost shell. The Fe II lines are supposed to come from the expanding photospheric layer wheras the (weak) Sc II lines are formed at a even smaller radius.
Limitation: In [7] they have detected Sc II lines only in spectra of SN age older than 77 d due to SNR. Hence my labeling may be wrong. In my spectrum from 2017-06-24 the supernova 2017eaw is much younger.
PCP - P-Cygni profile


I measured the blue shifted absorption feature of H-Alpha in the following spectra:

Part of spectrum from 2017-05-21 of sn2017eaw with blue shifted H-Alpha absorption detail
In spectrum from 2017-05-21 the value of blue shift is 273.4 Å against the rest wavelength at 6562.8 Å. This corresponds to a radial velocity of 12489 km/s of the ejected material (with correction of z=0.00015 from host galaxy NGC 6946).

Part of spectrum from 2017-05-26 of sn2017eaw with blue shifted H-Alpha absorption detail
In spectrum from 2017-05-26 the value of blue shift is 247.5 Å against the rest wavelength at 6562.8 Å. This corresponds to a radial velocity of 11307 km/s of the ejected material (with correction of z=0.00015 from host galaxy NGC 6946).

Part of spectrum from 2017-06-10 of sn2017eaw with blue shifted H-Alpha absorption detail
In spectrum from 2017-06-10 the value of blue shift is 177.2 Å against the rest wavelength at 6562.8 Å. This corresponds to a radial velocity of 8097 km/s of the ejected material (with correction of z=0.00015 from host galaxy NGC 6946).

Part of spectrum from 2017-06-24 of sn2017eaw with blue shifted H-Alpha absorption detail
In spectrum from 2017-06-24 the value of blue shift is 172.3 Å against the rest wavelength at 6562.8 Å. This corresponds to a radial velocity of 7870 km/s of the ejected material (with correction of z=0.00015 from host galaxy NGC 6946).

Part of spectrum from 2017-07-08 of sn2017eaw with blue shifted H-Alpha absorption detail
In spectrum from 2017-07-08 the value of blue shift is 149.1 Å against the rest wavelength at 6562.8 Å. This corresponds to a radial velocity of 6809 km/s of the ejected material (with correction of z=0.00015 from host galaxy NGC 6946).

Part of spectrum from 2017-07-16 of sn2017eaw with blue shifted H-Alpha absorption detail
In spectrum from 2017-07-16 the value of blue shift is 140.1 Å against the rest wavelength at 6562.8 Å. This corresponds to a radial velocity of 6402 km/s of the ejected material (with correction of z=0.00015 from host galaxy NGC 6946).

Part of spectrum from 2017-07-29 of sn2017eaw with blue shifted H-Alpha absorption detail
In spectrum from 2017-07-29 the value of blue shift is 136.8 Å against the rest wavelength at 6562.8 Å. This corresponds to a radial velocity of 6248 km/s of the ejected material (with correction of z=0.00015 from host galaxy NGC 6946).

Part of spectrum from 2017-08-27 of sn2017eaw with blue shifted H-Alpha absorption detail
In spectrum from 2017-08-27 the value of blue shift is 128.0 Å against the rest wavelength at 6562.8 Å. This corresponds to a radial velocity of 5846 km/s of the ejected material (with correction of z=0.00015 from host galaxy NGC 6946).



Spectra evolution (in days since explosion):

spectra evolution of supernova 2017eaw
The H-Alpha emission becomes stronger, the blue shift of absorption feature becomes less in wavelength and stronger in intensity, hence the ejected material is slower. There is a lack of light in the blue part in later spectrum. This matches to the observed increase of color index, see B-V diagram of SN 2017eaw.



References:
[1] Harutyunyan et al., 2008, A&A, 488, 383
[2] Blondin & Tonry 2007, ApJ, 666, 1024
[3] R.O. Gray, C.J. Corbally, Stellar Spectral Classification, Princeton University Press, 2009
[4] ATEL #10377, http://www.astronomerstelegram.org/?read=10377
[5] A.V. Filippenko, Optical Spectra of Supernovae, Annu. Rev. Astron. Astrophys. 1997. 35,309,55, https://ned.ipac.caltech.edu/level5/March03/Filippenko/paper.pdf
[6] G. Dhungana et al., Extensive Spectroscopy and Photometry of the Type IIP Supernova 2013ej, 2016, ApJ,822,1, http://iopscience.iop.org/article/10.3847/0004-637X/822/1/6/meta
[7] Bose et al., SN 2013ab: a normal Type IIP supernova in NGC 5669, MNRAS 2015, 450 (3), 2373-2392, https://arxiv.org/abs/1504.00838


My other spectroscopic observations: Spektroskopie (German)



[ updated: 2018-01-20 | Email icon Gregor Krannich | Homepage Gregor & Cornelia Krannich ]