Supernovae

Josefine Selj, Dmitry Sharapov, Auni Somero, Linda Östman

supervisor: Jesper Sollerman

NORDFORSK Summer School on Observational Astrophysics at NOT and SST

27.6.-8.7.2006, La Palma, Canarian Islands

Outline

● Motivation

● Supernovae

– what are they?

● Preparations

● Observations

● Reductions

● Results

● Summary

Motivation

● Nucleosynthesis

● Production of neutron stars and black holes

● Origin of cosmic rays

● Interstellar matter

● Induced starformation

● Type Ia – standard candles. Used to measure the expansion of the universe. Are they really reliable?

Supernovae● The spectacular explosions of massive stars

ending their lives● Two different types of progenitors:

– thermal burning of a white dwarf binary, Ia

– core collapse of massive stars

The supernova

family tree

showing how

they are related

Supernovae type Ia

● Homogeneous – used as standard candles

– By plotting their distance vs their velocities (since

they are equally bright!) you find how the Hubble

flow has changed.

● Result from a carbon-oxygen white dwarf accreting matter from a close companion star until it reaches the Chandrasekhar limit (1.4 M_s)

Supernova type Ia, spectra

● Lack of hydrogen

● Early time spectra exhibit prominent broad peaks and valleys,

lines come from O, Mg, Si, S, Ca. Strongest features are Si ll

line at 6355 Å and Ca H&K at ~3950 Å

● Nebular phase spectra (~begins 1 month after max) are

dominated by forbidden emission lines of Fe

● Late time Ia are powered by the decay of radioactive Co

Supernova type II

● Atomic nuclei fused to the end of the road: iron

● No higher radiation pressure, kept up by degeneracy pressure of

electrons

● When core exceeds Chandrasekhar limit -> Collapse!

Supernova type II, spectra

Subclasses and their spectra:

-Type II-L - linear decrease in their light curve (linear in magnitude vs time) featureless and blue at early times

-Type II-P – reach a plateau in their light curve, featureless and blue at early times. At the plateau one finds strong Balmer lines and Ca ll H&K. Late time spectra have strong H_alpha and emission lines from OI and CaII

-Type IIn – narrow emission lines, may be produced by the interaction of the ejecta with dense circumstellar material. Slowly declining light curves.

Spectra comparison• Spectra of SN2006dh (typical Ia) and SN2006ca (typical type II)

Ia has (1) broader features, (2) a Si absorption line at 6355 Å, (3) Ca II abs lines at ~3950 Å

II has (1) P Cygni profiles, (2) a strong H_alpha emission line at 6863 Å, (3) Ca II absorption line at

8500, (4) Na I abs line at ~ 5800 Å. The absorption at ~ 7600 Å is atmospheric

Preparations

• Finding our targets- Bright supernovae- Visibility plot- Exposure time estimates- Night schedule - Finding charts

• What do we want- Spectroscopy, which grism, slit?

- Photometry, which filters?

• Calibration data- fields at same airmass

- in right filters and grisms/slits

Observations 2/7

● First half of the night, with ALFOSC:

SN2006bp –photometry (BVR) and spectroscopy (gr 4)

SN2006cz – photometry (BVR) and spec. (gr 4)

SN2006dh – photometry (UBVRi) and spec. (gr 4)

SN2006cu – photometry (VR) and spec. (gr 7)

+ spec. flats (Halogen), arc lamps (He, Ne), twilight flats, photometric and

spectroscopic standards. grism #4: 3200 – 9100 Å, grism #7: 3850 – 6850 Å,

slit width 1.3”

Observations 4/7

Second half of the night, with ALFOSC:

SN2006ca – photometry (BVRi) and spec. (grism 4)

SN2006cm – photometry (VR) and spec. (grism 4)

SN2006dm –photometry (R) and spec. (grism 4)

SN2005hk – photometry (UBVRi) and spec. (grism 4)

+ spec. flats, arclamps, twilight flats, spectroscopic and photometric standards

Observations 6/7

• First three hours of the night, with NOTCam:- SN2005dh – photometry (JKsH)

- twilight flats and standard field

• 3x3 dithering (10' between each images) with offset of 3' to North and 30” to the West for sky

• We managed to use autoguiding

Data reduction

● The most time consuming part of this project so far...

● IRAF for data reduction (zerocombine, flatcombine, ccdproc)

– photometry: phot,

– spectroscopy: apall, identify, hedit, dispcor, calibrate

– IR: Amanda's scripts ● IDL for plotting the spectra

SN2005hk, type Ia

• Our first main target: SN2005hk, old special type Ia– What is special: very narrow lines -> small velocities– Resembels SN2002cx (low expansion velocities, slow late time

declination. Premitted Fell lines and possible OI in late spectra, many narrow lines, late time spectra looks like early time spectra)

– Spectral energy distribution of SN2005hk and the young SN2006dh

– Spectra of SN2005hk and a young Ia, SN2006dh– Lightcurve of SN2005hk and SN2002cx

Comparing energy vs frequency for SN2005hk and

SN2006dh, plotted for BVRi

Lightcurve for SN2005hk. Our points are the last four, the second last date is from D1.5 at la Silla.

Here: B (black), V-1 (green), R+2 (blue) and i-3(red)

Comparing the lightcurves of SN2005hk and SN2002cx

Spectrum of SN2005hk and the young type Ia

SN2006dh

SN2006dm, Ia – almost new!• Filippenko classified it first, but we could give additional information -> CBET

circular, confirming that it is a type Ia, most similar to the subluminous SN2000dk.

• The comparison spectra:

SN2006cz, type Ia

• Resembles 91T– overluminous

• Photometry – BVR

– slightly broader

lightcurve

SN2006dh, young type Ia

● This supernova we looked at in all available filters; UBVRi JHKs

J

Ks H

IR observations of SN 2006dh

Energy distribution of 2006dh

Spectrum of SN 2006dh Ia

• Broad peaks and valleys

• Ca II H&K 3955 Å abs line

• Si II at 6355 Å abs

• Fe II (visible after 2 weeks)

• O,Mg,Si,S,Ca

SN2006cm, type Ia

• Doesn't look like a typical Ia (needs a closer look)

• Overluminous

• Older than the other Ia spectra we have looked at

SN2006bp, type II-P

• A supernova in the nebular phase - when the ejected matter becomes optically thin.

• Late time emission is powered by radioactive decay of Co and Fe.

• Photometry B (green) V (red) R (yellow)

Spectra of SN2006ca and SN2006bp (both type II)

Spectrum of SN2006cu, type IIn

• Note: this spectrum is off in the wavelength calibration

• Narrow emission lines, may result from dense circumstellar material.

• H_alpha emission line at 6563Å

• H_beta 4861• Balmer

emission lines

Summary

● We observed 8 SNe of several different types

– both typical and peculiar

SN Type Photometry Spectra

2005hk Ia – similar to 02cx (U),B,V,R,i Grism 42006dm Ia – young R Grism 42006cz Ia – 91T like B,R,V Grism 42006dh Ia – young U,B,V,R,i,J,(H),Ks Grism 42006cm Ia – peculiar?? V, R Grism 42006bp II-P V, R Grism 42006ca II V, B, i Grism 42006cu II n V, R Grism 7

Twinkle twinkle little star

Now we know just what you are

Making atoms in your core

Helium and many more

Twinkle twinkle little star

Now we know just what you are.

Twinkle twinkle little star

How I've wondered what WE are

Now I know you're made of dust

Now I know you're just like us

Twinkle twinkle, oh so far

Now I know I am a star.

●We did both photometry and spectroscopy

– optical and infrared●More detailed analysis to be done

Summary

SN Type Photometry Spectra

2005hk Ia – similar to 02cx (U),B,V,R,i Grism 42006dm Ia – young R Grism 42006cz Ia – 91T like B,R,V Grism 42006dh Ia – young U,B,V,R,i,J,(H),Ks Grism 42006cm Ia – peculiar?? V, R Grism 42006bp II-P V, R Grism 42006ca II V, B, i Grism 42006cu II n V, R Grism 7