The Photometric and Spectral Evolution of the 2008 NGC 300 Transient

Roberta M. Humphreys

University of Minnesota

Prieto 2008 fromSpitzer 2003, 2007

Discovery April 24, 2008 by Monard

Smarts 1.3m BVRIJHK May 15 – Jun 22, 2009

1.5m spectroscopy May 15 - Jan 22, 2009

Magellan MagE July 6, Aug 30/Sep 1 2008, Jun 05, 2009

The progenitor

Basic Properties

Pre-eruption IR SED => Lsun = 5.5 x 104 Lsun, Mbol = -7.1 mag

Maximum light mv = 14.7 mag => Mv = -12.1 or -12.9 mag, Av = 0.3 or 1.2

Increased luminosity by ~ 100 times or more

Spectrum at max, F-type supergaint abs line + H, Ca II, [Ca II] emission

Total emitted energy ~ 1047 ergs

Mass of progenitor ? 10 – 15 Msun

The Spectral Energy Distribution

7500 K BB, f-f, 715 K dust

R* max = 10AU

Rdust = 1750 AU = 10 light days

Dust survived the initial eruption

L* = 1.3 x 107 Lsun

observed corrected

Evolution of the Spectrum – the Eruption

Berger et al. 2009 Bond et al. 2009

F-type supergiant spectrum expected in an eruption forming optically thick wind

At max – complex Ca II profiles, Vel (em and abs) ~ 400 km/s, FWHM of H ~ 1000 km/s

The Double-Peaked Hydrogen and Ca II Emission Lines

bipolar/asymmetric outflow –

expansion

Ca II primary 79 km/s

secondary 164 km/s

Hydrogen primary 69 km/s

secondary ~ 200 km/s

Evolution of the Spectrum – Post-Eruption

Ca II and [Ca II] Emission

The Asymmetric [Ca II] profiles Thomson scattering

Auer and Van Blerkom 1972 demonstrated effect of electron scattering on profiles in expanding ejecta for recombination lines -- asymmetric profiles with red wings.

Hillier 1991

Other Emission Lines

He I 5876 + other weak em 7065, 6678, 3964, 3888

O I 8446 -- Ly pumping, by flourescence

[O I] 6300, 6363

Fe II

[Fe II]

The Absorption Line Spectrum

O I 7774 (lum sensitive ~ -6.9 Mv )

Sr II, Ca I, Mn I, Ti II, V II

Double Ca II H and K

Ba II : 4554, 4934

Rapid transition from absorption to emission Jul 18 (abs) Sep 08 (em)

Expanding envelope becoming transparent to ionizing radiation

Na I D (also O I 8446, Berger et al. )

Clues from the Velocities

Max . 15 May Em. and abs. ~ 400 km s-1

Post-eruption --

Double-peaked profiles ( abs min.Ca II and H) 200 +/- 2.7 km s-1 (14)

Emission lines (Aug/Sep) 200 +/- 4.4 km s-1 (40)

Absorption lines (July) 180 +/- 1.7 km s-1 (33)

Expected Vel galactic rotation 190 km s-1

Eruption and Post – Eruption

Maximum – redshifted vel ~ 400 km/s expansion ~ 500 km/s,

Post-eruption – 20 – 30d -- shift to lower vel abs and em lines

Initial eruption followed by a dense slowly expanding false photosphere and asymmetrical bipolar outflow

Abs lines weaken, transition to em (Na I and O I)

100d dense wind becomes transparent to ionizing radiation

Thoughts on the nature of the N300 Transient and origin of instability

Progenitor (IR SED) a high mass loss state, tip of AGB or supergiant OH/IR star

lack of IRAC variability, outflow velocity (75 km s-1) post AGB/RSG

Outflow vel. greater than AGB/RSG, lower S Dor vars.

Initial mass -- Lum 10-15Msun, 13-17Msun CMD (Gogarten et al. 2009)

PAH feature/ Ba II? post AGB, proto-PNe, lower initial mass

But no carbon bands: CH, CN, C2

Origin of the ionizing radiation

Intermediate-mass post -AGB/RSG on a blue loop

Other members of this sub-group

SN2008S

SN2010da

SN2010dn

M85 2006 OT?

M31 RV X

At Maximum:

F-type supergiant spectrum, Ca II and [Ca II] em, dusty progenitors, increased 100 – 1000 times in luminosity

NGC 300 2008 OT SN2008s SN2010da

Optically obscured, “cool” transients

Prieto 2008 Prieto et al 2008 Khan et al., Berger et al. 2010

T= 350K BB L = 5.5 x 104 Lsun, Mbol = -7.1 mag

at maximumMv = -12.1 or -12.9 mag

L = 1.1 x 107 Lsun

T= 440K BB

L = 3.5 x 104 Lsun Mbol = -6.8 mag

at maximum Mv = -13.6 mag

L = 3 x 107 Lsun

T= 890 K BB

L = 1.3 x 104 Lsun

Mbol = -5.5 mag

at maximum Mv = -10.4 mag

L = 1.1 x 106 Lsun

In “eruption” increased 100 – 1000 times

SN2010da spectrum

H em, [N II], He I, O I,

Ca II ? No [Ca II] !

He II 4686 !

ATEL 2637 (Chornock & Berger)

The spectra

These are not LBVs !

Outstanding Theoretical Problems in Massive Star Research

A future meeting --

Minnesota Institute for Astrophysics and

Fine Theoretical Physics Institute

University of Minnesota October 2012

IMPOSTOR !

A candidate for membership?

UGC 2773 2009 OT

At max ~ 107 Lsun

Increased 22.8 -> 17.5 mR

Progenitor -7.8 Mv

Color -> ~ A-type 1.3 x 105 Lsun

~ 20Msun (CMD)