Research activities - Henrik Hartman, Lund Observatory

My research interest is atomic astrophysics, including e.g. spectral analysis of emission line objects (spec. Eta Carinae), excitation mechanisms and laboratory measurements needed for the interpretation of astronomical spectra. Below some of my current projects are briefly described. Projects are performed in collaboration within the Atomic Astrophysics group. Other collaborators are mentioned in connection to the projects.
My research is supported by Vetenskapsrådet (Swedish Research Council) through a Forskarassistent (Junior Research Position).
Please see my list of publications for more details and (p)reprints.

 

Eta Carinae

Eta Carinae is one of the most massive and luminous stars know. With an estimated mass of more than 100 solar masses and a luminosity of several millions that of the sun, it in 6 seconds emits one full-year equivalent of solar radiation.

In the 1840's it went through a 'Great Eruption', expelling the around 10 solar masses of material today seen as the bipolar shape known as the Homunculus. For several years it was the second star in the sky, only outshined by Sirius. Today it has faded to be barely visible to the naked eye. A lesser eruption in 1890 produced a similar shaped 'Little Homunculus' residing inside, but detected in spectroscopic observations. In addition to the large eruptions, eta show a periodic behaviour of 5.54 years. Stable periods are interrupted by spectroscopic events, when the spectrum changes rapidly, on a time scale of days, in many wavelength regions from radio through ultraviolet and visible to X-rays. What cause the eruptions and the periodic spectroscopic events is not clear. There are indirect indications that the central object is a binary star with a highly eccentric orbit.

Eta Carinae in different wavelength regions: radio, infrared, optical and X-ray. The X-ray image covers a ~3 times larger area on the sky. Credits: ATCA (S.White); CTIO (E.Polomski); HST (NASA/J.Morse/K.Davidson); Chandra (NASA/CXC/SAO).



HST/STIS Spectroscopy of Eta Carinae and its ejecta

Within a Hubble Space Telescope (HST) Treasury project, we have observed Eta Carinae around the spectroscopic event of June 2003. With complementary observations we have covered the full spectroscopic cycle, which is a base for the studies of the temporal, spectral and spatial changes in the spectrum. HST/STIS observations of the Eta Carinae Nebula reveal a spatial region which is different from other regions as forbidden lines from ionized strontium, denoted [Sr II], are present in the spectrum. Sr is produced via slow neutron capture (s-process) and rarely shows forbidden emission lines. Ti II is also strong in emission whereas lines from hydrogen and helium are absent. The forbidden lines, i.e. radiative decay from metastable levels, can not be detected in laboratory sources but are often observed as strong lines in astrophysical plasmas.

The Weigelt blobs, seen 0.2" from the central object do also show a rich emission line spectrum, but totally different one. The excitation an ionization balance is clearly non-LTE, and selective ionization and excitation is significant. These gas condensations also host the only natural LASER observed.
External collaborators: Goddard Space Flight Center, Greenbelt; Centro de Fisica, IVIC, Venezuela


Sketch of the STIS slit positioned on the nebula, giving the 2D-spectrum (spatial vs. spectral scale) and the extracted 1D-spectrum.


Excitation processes in astrophysical plasmas

In some emission line objects selectively excited emission lines from different elements are observed. The most well-known case is the Bowen mechanism which redistributes He II radiation at 303 Å to O III optical emission. We observe strong enhanced Fe II emission from selected high-lying states generated by absorption of mainly H Lyman alpha, but also strong lines of other elements.

As mentioned above, in the Weigelt blobs we observe also more rare processes, such as selective ionization and excitation.
Coll.: Institute of Spectroscopy, Moskow, Russia



Laboratory measurements at Max-lab synchrotron source

FeII is an important element i many astrophysical sources, both galactic stars and more distant objects such as quasars and AGNs. To use transitions for quantitative analysis the intrinsic strength (oscillator strength or transition probability) need to be known. For some transitions, the level mixing is strong and makes the strengths difficult to calculate accurately.

We will measure some of these transitions using an absorption experiment at the Max-lab synchrotron. Specifically lines that are needed in the work on fluorescence pumping in many emission line objects. The measurements will be combined with local measurements using an emission line source to tie together sets of lines and put them all on an absolute scale.
External collaborator: Stacey Sörensen, LU



Lifetime measurements of metastable levels at CRYRING

From dilute astrophysical plasmas such as planetary nebulae or stellar winds are observed emission lines that are not seen in laboratory sources or stellar atmospheres. These originate from metastable levels, i.e. longlived excited states with lifetimes of ms to s. 'Ordinary' excited states usually have lifetimes of the order of ns. The lifetimes of metastable states are often used in modeling and diagnostics of these dilute astrophysical plasmas.

At the CRYRING facility in Stockholm we perform lifetime measurements of levels from which some of the forbidden lines we observe in the different locations of the Eta Carinae object originate(see above).
Collaborators: Atomic Physics Group, Stockholm University; Atomic Physics, Lund Institute of Technology




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Henrik Hartman: Publications

Last updated: September 14, 2006