Transient surveys

I am involved in the intermediate Palomar Transient Factory (iPTF), which discover supernovae at optical wavelengths by systematically imaging the sky, several times per night, with the robotic Palomar 48-inch telescope.

I’m also part of the the Spitzer Infrared Intensive Transients Survey (SPIRITS), which is the first survey of its kind, exploring the dynamic infrared sky.


Supernovae are the explosive deaths of stars. Since stars of different mass follow different evolutionary tracks they face different end stages, which gives rise to a large variety of luminosities and spectral features among the supernovae.

One special type of supernovae, Type Ia, appears to always explode with the same brightness, making them useful as distance indicators. The acceler1ated expansion of the Universe was discovered using SNe Ia, leading to Perlmutter, Schmidt & Riess being awarded the Nobel Prize in 2011. While the use of SNe Ia remains essential for the studying the properties of the “dark energy” driving this accelerated expansion, the lack of understanding of the SN progenitor systems and the empirically derived standardization corrections represent severe limitations for SNe Ia as cosmological probes.

Cosmic dust

One astrophysical source of uncertainty in supernova observations comes from cosmic dust particles. Dust in the circumstellar (CS) environment of SNe, in the insterstellar medium of SN host galaxies and possibly even in the intergalactic medium have important implications for the observed colors and luminosities of SNe Ia; typically making them redder and fainter.

By measuring the wavelength dependence of the dust extinction from UV-to-IR observations and using other proxies for dust (such as Sodium absorption lines in high-resolution spectra) there is increasing evidence that some SNe show evidence for unusual dust. This, together with time-varying blue-shifted Sodium absorption, could indicate the presence of dust in the CS environment. Detecting or constraining the amounts of CS dust also has implications on the progenitor systems.



Recent papers:

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Office 63401
Department of Physics and Astronomy,
Ångström Laboratory at Uppsala University
P.O Box 516, SE-751 20 Uppsala


018-471 5990


joel.johansson @