What Makes Supernova 2008ha Unique and How Did a 14-Year-Old Discover It?

[Astronuc]

The story about SN2008ha
http://deer-pond-observatorie.wetpaint.com/page/The+story+about+SN2008ha?t=anon
How Caroline became the youngest person to discover a supernova
..................

On November 13th 2008, Caroline Moore a member of the Puckett Observatory Supernova Search team was recognized by the International Astronomical Union for discovering a supernova. Their discovery has been named Supernova 2008ha in galaxy UGC 12682. And at the ripe old age of 14, Caroline has also been recognized as most likely the youngest person to discover a supernova.

iOptron Announces Caroline Moore as the Young Astronomer of the Year
http://www.prweb.com/releases/2009/02/prweb1965644.htm
Supernova 2008ha is in UGC 12682, a galaxy that is eating itself and where Supernovae normally do not occur. This is one of the things the makes Caroline's discovery so unique. It is also a type 1a supernova and possibly the least luminous supernovae ever observed.


http://www.supernovae.net/sn2008/sn2008ha.html

http://www.cometwatch.com/
The Puckett Observatory is a Private facility owned and operated by Tim Puckett. The observatory is located in the North Georgia mountains and is dedicated to the study of comets and the discovery of supernovae.


This supernova is attracting a lot of interest.

SN 2008ha: An Extremely Low Luminosity and Extremely Low Energy Supernova
http://arxiv.org/abs/0902.2794

Authors: Ryan J. Foley, Ryan Chornock, Alexei V. Filippenko, Mohan Ganeshalingam, Robert P. Kirshner, Weidong Li, S. Bradley Cenko, Pete Challis, Andrew S. Friedman, Maryam Modjaz, Jeffrey M. Silverman, W. Michael Wood-Vasey
(Submitted on 16 Feb 2009 (v1), last revised 23 Feb 2009 (this version, v2))

Abstract: We present ultraviolet, optical, and near-infrared photometry as well as optical spectra of the peculiar supernova (SN) 2008ha. SN 2008ha had a very low peak luminosity, reaching only M_V = -14.2 mag, and low line velocities of only ~2000 km/s near maximum brightness, indicating a very small kinetic energy per unit mass of ejecta. Spectroscopically, SN 2008ha is a member of the SN 2002cx-like class of SNe, a peculiar subclass of SNe Ia; however, SN 2008ha is the most extreme member, being significantly fainter and having lower line velocities than the typical member, which is already ~2 mag fainter and has line velocities ~5000 km/s smaller (near maximum brightness) than a normal SN Ia. SN 2008ha had a remarkably short rise time of only ~10 days, significantly shorter than either SN 2002cx-like objects (~15 days) or normal SNe Ia (~19.5 days). The bolometric light curve of SN 2008ha indicates that SN 2008ha peaked at L_peak = (9.5 +/- 1.4) x 10^40 ergs/s, making SN 2008ha perhaps the least luminous SN ever observed. From its peak luminosity and rise time, we infer that SN 2008ha generated (3.0 +/- 0.9) x 10^-3 M_sun of 56Ni, had a kinetic energy of ~2 x 10^48 ergs, and ejected 0.15 M_sun of material. We classify three new (and one potential) members of the SN 2002cx-like class, expanding the sample to 14 (and one potential) members. The host-galaxy morphology distribution of the class is consistent with that of SNe Ia, Ib, Ic, and II. Several models for generating low-luminosity SNe can explain the observations of SN 2008ha; however, if a single model is to describe all SN 2002cx-like objects, either electron capture in Ne-Mg white dwarfs causing a core collapse, or deflagration of C-O white dwarfs with SN 2008ha being a partial deflagration and not unbinding the progenitor star, are preferred. Abridged.

A low energy core-collapse supernova without a hydrogen envelope
http://arxiv.org/abs/0901.2074

Stefano Valenti (1), Andrea Pastorello (1), Enrico Cappellaro (2), Stefano Benetti (2), Paolo Mazzali (2,3), Jose Manteca (4), Stefan Taubenberger (3), Nancy Elias-Rosa (5), Rafael Ferrando (6), Avet Harutyunyan (2,7), Veli-Pekka Hentunen (8,9), Markku Nissinen (8), Elena Pian (10), Massimo Turatto (11), Luca Zampieri (2), Stephen J. Smartt (1). ((1) Queen's University Belfast, (2) INAF-OAPD Padova, (3) MPA Garching, (4) Begues Observatory Barcellona, (5) Caltech Pasadena, (6) Arguines Observatory Segorbe, (7) TNG Santa Cruz de la Palma, (8) Taurus Hill Observatory Kangaslampi, (9) Tuorla Observatory Piikkio, (10) INAF-OAT Trieste, (11) INAC-OACT Catania)

The final fate of massive stars depends on many factors, including mass, rotation rate, magnetic fields and metallicity. Theory suggests that some massive stars (initially greater than 25-30 solar masses) end up as Wolf-Rayet stars which are deficient in hydrogen because of mass loss through strong stellar winds. The most massive of these stars have cores which may form a black hole and theory predicts that the resulting explosion produces ejecta of low kinetic energy, a faint optical display and a small mass fraction of radioactive nickel(1,2,3). An alternative origin for low energy supernovae is the collapse of the oxygen-neon core of a relatively lowmass star (7-9 solar masses) through electron capture(4,5). However no weak, hydrogen deficient, core-collapse supernovae are known. Here we report that such faint, low energy core-collapse supernovae do exist, and show that SN2008ha is the faintest hydrogen poor supernova ever observed. We propose that other similar events have been observed but they have been misclassified as peculiar thermonuclear supernovae (sometimes labelled SN2002cx-like events(6)). This discovery could link these faint supernovae to some long duration gamma-ray bursts. Extremely faint, hydrogen-stripped core-collapse supernovae have been proposed to produce those long gamma-ray bursts whose afterglows do not show evidence of association with supernovae (7,8,9).

 

[Chronos]

Fascinating. Thanks for the link. Learn something new every day.

 

[seerongo]

The statement about low luminosity confuses me. Perhaps I'm confusing terms such as "luminosity" and "peak light output" or "brightness", but I thought that all type 1a SNe were considered to have pretty much equal light output which is what allows them to be used as "standard candles" for measuring distance. I thought at first that what they meant was that this SN is just very far away so appears very dim, but the text of the paper seems to imply that this SN is unusual for a type 1a. Does this maybe suggest that type 1a's cannot be relied on for this purpose?
I'm not a professional, so maybe I'm misinterpreting things.
Thanks.

 

[Chronos]

The papers Astronuc referenced indicate some dispute regarding the nature of this supernova. If it is a core collapse supernova, it is not your typical '1a' supernova, where hydrogen gas accretes on the surface of a white dwarf until it 'detonates' upon reaching a critical mass. It could still, however, be a 1a where the accretion material was unusually hydrogen deficient. That is what is being debated IMO.

 

[seerongo]

http://supernovae.in2p3.fr/~bongard/SeriousSeb/Revue_presse/revue_presse_2009-01-21.txt"

Thanks for your reply. This piqued my interest, so I did a little more digging and found the above link. The first two of the abstracts refer to this supernova.

Note especially the last sentence of the first one:

arXiv:0901.2476
Date: Fri, 16 Jan 2009 13:22:04 GMT (42kb)

Title: The Mean Type Ia Supernova Spectrum Over the Past 9 Giga years
Authors: M. Sullivan, R. S. Ellis, D. A. Howell, A. Riess,
P. E. Nugent, A.
Gal-Yam
Categories: astro-ph
Comments: Accepted for publication in ApJ Letters

We examine the possibility of evolution with redshift in the mean
rest-frame ultraviolet (UV; <4500A) spectrum of Type Ia Supernovae
(SNe Ia) sampling the redshift range 0<z<1.3. We find new evidence for
a decrease with redshift in the strength of intermediate-mass element
(IME) features, particularly Si II and to a lesser extent Ca II "H&K"
and Mg II blends, indicating lower IME abundances in the higher
redshift SNe. A larger fraction of luminous, wider light-curve width
(higher "stretch") SNe Ia are expected at higher redshift than
locally, so we compare our observed spectral evolution with that
predicted by a redshift-evolving stretch distribution (Howell et
al. 2007) coupled with a stretch-dependent SN Ia spectrum. We show
that the sense of the spectral evolution can be reproduced by this
simple model, though the highest redshift events seem additionally
deficient in Si and Ca. We also examine the mean SN Ia UV-optical
colors as a function of redshift, thought to be sensitive to
variations in progenitor composition. We find that the expected
stretch variations are sufficient to explain the differences, although
improved data at z~0 will enable more precise tests. Thus, to the
extent possible with the available datasets, our results support the
continued use of SNe Ia as standardized candles.

This one proposes reclassifying it as a type 1b/c:

arXiv:0901.2074
Date: Wed, 14 Jan 2009 18:01:17 GMT (1372kb)

Title: An extremely faint stripped-envelope core-collapse supernova
and its implications
Authors: Stefano Valenti, Andrea Pastorello, Enrico Cappellaro,
Stefano
Benetti, Paolo Mazzali, Jose Manteca, Stefan Taubenberger, Nancy
Elias-Rosa,
Rafael Ferrando, Avet Harutyunyan, Veli-Pekka Hentunen, Markku
Nissinen,
Elena Pian, Massimo Turatto, Luca Zampieri, Stephen J. Smartt
Categories: astro-ph
Comments: submitted 12 January 2009 - comments are welcome

The final fate of massive stars depends on many factors, including the
mass of the helium core, rotation rate, magnetic fields and
metallicity. Theory suggests that some massive stars (initially
greater than 25-30 solar masses) can die as under-luminous
core-collapse supernovae (Ref.1,2,3). The models propose that the core
mantle falls back onto the collapsed remnant, mass accretion leads to
black hole formation and the remaining envelope including a very small
fraction of radioactive elements is ejected with low kinetic energy.
An alternative origin for low energy supernovae is the collapse of the
oxygen-magnesium-neon core of a relatively low-mass star (7-8 solar
masses) through electron capture (Ref 4,5). Only under-luminous type
II-plateau (IIP) supernovae have been discovered so far (e.g. Ref. 6),
and no weak hydrogen-stripped core-collapse supernova (of type Ib/c)
has been detected. Here we show that faint Ib/c Supernovae do exist,
and that they have been previously misclassified as peculiar
thermonuclear supernovae (sometimes labelled 2002cx-like events,
Ref. 7). We propose that the most recently discovered event of this
class, SN2008ha, is a type Ib/c supernova and one of the faintest
core-collapse events ever observed. This discovery has implications in
linking supernovae to gamma-ray bursts. Extremely faint,
hydrogen-stripped core-collapse supernovae have been proposed to
produce those long gamma-ray bursts whose afterglows do not show
evidence of associated supernovae (Ref. 8,9,10). However until now
these supernovae have remained undiscovered in the local Universe.

Anyway, it got me to learning a bit more about all this.

 

[Chronos]

You have dug deeper than I, but, found the essential nature of the discussion. Good links.