We aim to determine the current expansion rate of the
Universe, the so-called Hubble constant H0. To
this end, we measure distances to Type IIP supernovae
in the Hubble flow using the Tailored Expanding Photosphere Method.
This project is based on the ESO-VLT Large Programme 1104.A-0380.
This is the basic principle how the Expanding Photosphere Method (EPM) works:
As usual, the devil is in the details, and this is what the adH0cc programme is about. We intend to obtain better distances than with classical EPM through tailored spectral modelling of the individual Type IIP supernovae in our sample.
To identify well suited Type IIP supernovae, adH0cc has to spectroscopically classify numerous transients. The outcomes of these classifications are reported in AstroNotes of the IAU Supernova Working Group. All adH0cc AstroNotes can be found here:
There is a great need for independent accurate measurements of the Hubble constant (H0). We establish a new one-step method to determine H0 based on radiative transfer modeling of type II supernovae and demonstrate its utility in a proof-of-principle measurement. In this first-ever application of the tailored-expanding-photosphere method in the Hubble flow, we find H0 = 72.3 ± 2.9 km s-1 Mpc-1 in good agreement with state-of-the-art results.
Type II supernovae that exploded in the same galaxy provide us with the exciting opportunity to measure the same distance twice and compare the results.
In the Whirpool galaxy, we can directly compare distances from three state-of-the-art methods: the EPM applied to supernova 2005cs, the Cepheid period-luminosity relation, and the tip of the red giant branch.
We aim to observe ~20 Type IIP supernovae in the redshift range from 0.04 to 0.10,
i.e., the linear Hubble flow. We are using the 8.2 m
VLT-UT1 telescope equipped with the
FORS2 spectrograph, where we have been granted 150 hr of observing time
through an ESO Large
Programme.
VLT images cutouts of our current sample of supernovae are shown below.
We are collecting spectral time series for the first month of the evolution of Type IIP supernovae, since this period is ideal for accurate spectral modelling to determine the distances of the supernovae.
The spectra are reduced using the custom-made FORSify
pipeline, which is based on PypeIt.
At the end of the adH0cc project, we will upload the fully reduced and calibrated data to the
ESO archive and make them available to the community.
Radiative transfer calculations with our code
TARDIS
allow us to predict the luminosity and spectrum for a supernova
model. To find a good model for an observed supernova, we adjust
the parameters of our simulated supernova until the predicted
spectrum matches the observation. In this step, we vary, for example,
the temperature, the velocity, and the abundances of various
chemical elements. Finally, the best fit model tells us the
luminosity and therefore the distance to the observed supernova.
Rubina Kotak (Turku)
Stéphane Blondin (CNRS, LAM)
Wolfgang Hillebrandt (PI, MPA)
Bruno Leibundgut (PI, ESO)
Geza Csörnyei (MPA)
Gabi Cudmani (MPA / TUM)
Andreas Flörs (GSI)
Alexander Holas (ZAH / HITS)
Sabrina Kressierer (ESO / TUM)
Jason Spyromilio (ESO)
Sherry H. Suyu (MPA / TUM / ASIAA)
Stefan Taubenberger (MPA)
Christian Vogl (MPA)
Rachel Bruch (Weizmann)
Avishay Gal-Yam (Weizmann)
Cameron Lemon (EPFL)
Stephen J. Smartt (QUB)
You want to learn more? Do not hesitate to contact us!
Wolfgang and Bruno are the PIs of adH0cc.
Bruno Leibundgut
European Southern Observatory
Karl-Schwarzschild-Str. 2
D-85748 Garching
Germany
Wolfgang Hillebrandt
Max Planck Institute for Astrophysics
Karl-Schwarzschild-Str. 1
D-85748 Garching
Germany