Uffe Gråe Jørgensen


Personal data:

     Name: Uffe Gråe Jørgensen
    Title: associate professor (Danish "lektor")

    Email: uffegj@nbi.dk
      Fax: +45 3532 5989
    Phone: +45 3532 5998
Secretary: +45 3532 5996

    The postal address of the institute is:
    Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
    For historical reasons, this building of the NBI is called the Rockefeller Complex (see map: "Rockefeller_Komplekset").
    My office is room 037, at the ground floor of the building to the left after entering the main entrance.


Research:

I started my scientific work with studies of molecular opacities (with my master thesis being on the absorption coefficients of HCN and C2H2), went deeper into the quantum chemistry of molecular processes, and broadened my studies to the application to cool stellar atmospheres (with my PhD thesis being on AGB stars and stellar atmospheres). In 2002 I shifted my main research area to exoplanets, inspired by the encounter with Penny Sacket and her PLANET team. Today, I am involved into instrument development of the lucky imaging technique for improved microlensing detection of small exoplanets, being in charge of the operation of the the Danish 1.54m telescope at ESO's La Silla observatory and in charge of the exoplanet research with the SONG telescope network. Throughout most of my life I have been fascinated with the unsolved questions in science. As a teenager I started a fast growing amateur astronomical association in the Copenhagen area, participated in forming the Scandinacian association of amateur astronomy, and in building a public observatory (a description of the development of our public observatory was recently summarized in a short interview) and a Danish amateur astronomy journal. In 2009 I had the great luck to be invited to be part of the creation of a Centre of Excellence, StarPlan, at Copenhagen University, with the main goal to understand whether our own solar system is normal or something unique. A list of most of my scientific papers can be found under U.G.Jorgensen at ADS, though a few have been misplaced under Graae-Jorgensen and similar, or have been published in more physics and/or chemistry oriented journals than covered by ADS.

My main areas of research are:

Exoplanets (planets around other stars):

Since 2002 I have been involved in the search for extrasolar planets by use of the microlensing technique; untill 2008 as part of the PLANET team, and since 2008 as part of the MiNDSTEp team, which I started and organizes together with Martin Dominik. Microlensing is complementaty to the other techniques for finding exoplanets, in the sense of being particular sensitive to planets in orbits similar to those in our own solar system, say from 1 AU to 10 AU. With the present set-up of telescopes and instrumentation the technique is sensitive down to approximately Earth-mass planets (the smallest, as of 2014, being a 1.6 Earth-mass planet in a Venus-like orbit), but with the development of the lucky imaging camera technology, microlensing should in principle be able to identify planets as small as Mars or even smaller. The theory of stellar microlensing was developed first by Einstein in 1936 (Science, vol.84, p.506-507), and later suggested to be able to reveal planets orbiting the lensing stars by Paczynski, Gould, and others. Several good descriptions about the theory of microlensing can be found on the web, eg. on the planet-legacy pages, the ARTEMiS pages, or just simply the Wiki- or Scholar-pedia pages. A short popular article in Danish, written by one of my former students Kennet Harpsøe, can be downloaded from the homepage of the journal Kvant.

In 1995 our team discovered, from the Danish telescope, what was then by far the most Earth-like exoplanet known. Although the planet is far from identical to the Earth (for one it is estimated to have a surface temperature of -200 Celcius degrees), it is Earth-like in the sense of having a mass (5.5 Earth-masses) and an orbit (2.6 AU) much more resembling the Earth than any other exoplanets that were known by then. The results were published in Nature, vol.439, p.437-440. together with Nature's comments to the discovery on page 400-401 in the same issue of the journal. ESO's press-release about the planet tells the story of the discovery, together with a short animation and an interview with me .

Microlensing allows to observe exoplanets at very large distances, including neareby other galaxies (although no planet outside our own Milky Way have yet been ideentified). All of the microlensing planets discovered so far have been identified due to the change in light of stars toward the centre of our own Galaxy where the density is high enough for the phenomenon to have a reasonable likelihood of happening. Typically a lensing star in this direction will be in the conficuration that will allow the discovery of orbiting planets once per almost a million years. Lensing observations is therefore a team-work of many telescopes that notify each other semi-automatically whenever a lensing anomaly is seen, to make sure that more telescopes observe the lensing planet when it is visible. By 2014 the total data-set of lensing curves contain approximately 50 events that seems to be due to planets, of which approximately half have such a quality that the parameters of the system has been well analyzed and published, including OB07368Lb, OB05071Lb, OB08310Lb, OB09387Lb, OB10073Lb, OB110251Lb, OB09266Lb and OB09319Lb. Since microlensing covers a parameter space not easily obtainable with any other method, the most important result from the analysis is how the statistical distribution of planetary masses and orbital distances are in this parameter interval. As opposed to other methods, quite stringent statistical conclusions can be drawn based on relatively few identified planets. Two central statistical studies that our group has been part of, conclude that there are more planets than stars in our Galaxy, that there are many more small-mass planets than high-mass planets, and that Jupiter-Saturn like planets in Jupiter-Saturn like orbits are relatively rare. This conclusion is in agreement with the statistical conclusions that can be derived from the radial velocity and transit surveys of exoplanets. In other words, Earth-like planets are common throughout the Milky Way, while Jupiter-Saturn like planets are rare. From the philosophical point of view of the Fermi paradox, one could ask whether this means that Jupiter-Saturn like planets in Jupiter-Saturn like orbits are central for the development of life on Earth-like planets further inside in thr habitable zone in the system, as probably was the case in our own solar system.

Stellar atmospheres and late stages of stellar evolution:

My early work on stellar atmospheres were on molecular opacities. When a molecule increase in size from 2 atoms to 3 or more atoms, the number of possible transitions increase substantially, because of the increase in modes and combinations between modes. While a typical diatomic molecule has a few thousand vibrational-rotational transitions of importance for the stellar spectrum and structure, the number of lines in just a tri-atomic molecule are counted in the millions. One of my first findings was that for polyatomic molecules, it is the veil of medium-strong lines that play the largest role for the atmospheric structure. In hindsight this is quite obvious; a figurative analogue could be the choice between sleeping covered in a thin blanket or a thick robe; the thinn veil of medium-weak lines block the radiation, creating a much larger backwarming effect on the atmosphere than the few strong lines would do, just as the blanket do to the heath of a sleeping body. When introducing the opacity of HCN to cool carbon star giants, the size of the model atmosphere expanded orders of magnitude, resulting in much better agreement with observed spectra, and for example solving the seeming paradox of atmospheric models showing carbon stars to be hydrogen poor, and it also quantified the huge effect logg (mass) had on the overall spectrum of giant stars. Over the coming years I improved my early order-of-magnitude estimates of the band-strengths (an early short conversation with Gerald Herzberg played an important role in getting these estimates more or less correct) to more detailed ab initio quantum chemical computations, in collaboration with Jan Almlöf, Per Siegbahn and Mats Larsson during my stay in Sweden. These and later studies include my work on opacities of HCN , C3 , water , methane, CIA (collision induced absorption processes), diamond dust, CH, CN, TiO, SiO, and other molecules which will (hopefully) all be available as line lists on this web page very soon again. Reviews of the molecular data were summarised at several occasions (including: 1, 2, 3). Unfortunately most of my line lists disappeared from my public ftp site a few years ago after a very unfortunate series of almost simultaneous disk and computer crashes together with a misunderstood agreement with the university about backups. I have also promised myself to re-establish my line list data base, hopefully very soon, making it again available from this web address.

In collaboration with Åke Nordlund, Bengt Gustafson, Kjell Erikson, Hollis Johnson, Aleksandra Borysow, Josef Hron, Susanne Höfner, and others, we investigated the effect on the stellar structure, with implication for the late stages of small- and medium-mass stars. These studies included reviews of the stellar atmosphere modelling, analysis of the effects spherical geometry, hydrodynamics), frequency dependence, the sampling (methods and -optimisation), tests of the models against spectral observations from space of carbon stars and of M-type giants, as well as wide spectral range (e.g. 5000 AA to 2.5 mu_m) comparisons of synthetic and ground-based observed spectra, and analysis of white dwarf atmospheres, and evolution.

I'm still working in this field occasionally. In 2008 we published an updated version of the MARCS code. It is the intention that this will be followed by a series of more detailed papers on various types of stellar atmospheres.

The formation and evolution of the solar system. My contribution to this field has mainly been concerning the origin of the material which the solar system is made of. We have extracted extrasolar diamonds and silicon_carbide grains from carbonaceous chondrieppe recent paper in the work of constructing a molecular opacity data base is the calculation of the absorption coefficient for water . ep recent paper in the work of constructing a molecular opacity data base is the calculation of the absorption coefficient for water . meteorites and measured their optical properties. By including these data in atmospheric modelling it is in principle possible to trace the stellar origin of the material that became the solar system. My original ideas about origin of the meteoritic extrasolar diamond (and SiC) dust in carbon stars were presented in paper in Nature in 1988. A recent description of our ideas about the stellar-meteoritic connection was presented at IAU Symposium 177.
I have also contributed to the solar system research with preditions and speculations about what will happen to the Sun and the Earth during the final phases of the evolution of the Sun (a short proceeding and a longer A&A paper, emphasizing different aspects), and with aspecta of the formation of the solar nebula and the formation of the Earth and its oceans (work in preparation).


The SCAN molecular data base:

C2
Information

CH
Information
Paper

CN
Paper

H2O
Line list
Information
Paper

SiO
Line list

TiO
Line list
Information
Paper


Teaching:

Courses I am teaching:

During recent years I have been teaching 3 graduate courses:
astrobiology, (in block 1 group A each second year; 2013, 2015, ...)
planetary physics (in block 3 group A each year)
spectroscopy (in block 2 group B each second year; 2014, 2016, ...)
and a bachelor course:
the solar system (in block 3 each year).

Thesis supervision:

I am presently supervisor for 3 PhD students:
Andrius Popovas on energy transport in protoplanetary disks (co-supervising with Åke Nordlund, NBI)
Diana Juncher on cloud formation in cool stars, brown dwarfs and exoplanetary atmospheres
Jesper Skorfelt on lucky imaging camera technology for exoplanet detection

Previous PhD students:
Kennet Harpsøe on the lucky imaging technique and microlensing
Christian Vinter on the search for exoplanets by use of the microlensing technique,
Juliana daSilva (co-advised with Luiz Vaz, Bel Horizonte, Brazil) on external illumination in stellar and exoplanetary atmospherers,
Stefan Wolf (co-advised with Poul Hjort, DTU) on Near-Earth asteroids; planning detection with the Gaia satellite.
Anja Andersen on dustformation in stars
Raul Jimenez on stellar evolution and the age of the Universe

Previous Master students:
Andrius Popovas on partition functions and opacity sampling methods,
Mads Sørensen, on the supernova rate in the solar neighbourhood (co-adviced with Henrik Svendsmark, DTU Space),
Sanne Hardis, The transiting exoplanet GJ1214b,
Joris Vos, on eclipsing binary stars (co-supervising with Jens Viggo Clausen, NBI),
Mikkel Mathiasen, Photometry on microlensing events
Kristian Woller on stellar abundance analysis,
Maha Jasim on the formation of the solar system,
Sitte Larsson on the formation of the solar system and dust formation in the collapsing disk,
Tobias Hinse on orbital computation (resonances, migration, etc) of exoplanets.
Claus Nielsen on comets and the Earth's atmosphere,
Christian Vinter on the search for exoplanets by use of the microlensing technique,
Dorte E. Rasmussen on cool white dwarfs,
Steen E. Jørgensen on laser communication with satellite (co-supervising with Flemming Hansen, DSRI)
Jens Falkesgaard on chemical equilibrium computations,
Søren Rasmussen on stellar atmospheres,
Peter Pedersen on the initial stellar mass function,
Christiane Helling on molecular opacities (co-supervising with Erwin Sedlmayr in Berlin),
Anja Andersen on pre-solar dust grains in meteorites,


Popularization:


A popular description of some of our science results include:
A description of our discovery of a ring around the small Centaur asteroide Chariklo, from NBI's, and from ESO's home pages.
The discovery of the Earth-like exoplanet OB05390, from ESO's text press release and in the format of a video animation and interview with me.
A sumary of our measurements of iridium abundances in samples collected at the 3.8 billion years old Isua region in Greenland, indicating that the Earth and the Moon was bombarded with 2000 tons of cometary material per square meter while Isua formed (in English and in Danish ).

General popular talks on the web include my short 2013 presentation in TV2 (Danskernes Akademi) about the chances of finding life on other planets, presented in an English version, and a Danish version, my 1/2 hour presentation for teachers in 2010 at NBI about the origin of water on the Earth, and a general and longer presentation that I am particularly happy with from the "Science and Coctails" arangement at Christiania in 2012.

Since 1995 I have had a fruitful collaboration with Bent Raymond Jørgensen on several series of public lectures, starting with our series of 25 TV broadcastings about natural science, history of science, philosophy, and its relation to religion. The series was first filmed at NBI and broadcated in DR1 in 1995, and later we made a technically better version in the television studios which was broadcasted in 1996/97 (a total of 25 broadcastings).
The series of lectures was issued in the form of a book with the titel "Videnskaben_eller_Gud?" ("Science or God?") in 1996, with a revised second edition in 1998 and revised and enlarged third edition in 2005. Bent has an overview of this and two later books at his homepage.


I regularly publish popular articles in various journals, for example:
U.G.Jørgensen, Aktuel Naturvidenskab (nr 12, 2012, p.16-20) about habitable exoplanets ("10 milliarder planeter som Jorden -- hvor er beboerne?").
U.G.Jørgensen, Berlingske. 2012 ; 02(11), 12 January 2012. p. 10
U.G.Jørgensen, Universitetets Almanak 2006 about exoplanets (2006).
U.G.Jørgensen, Naturens Verden about Tycho Brahe (NV, vol.84, nr.10, p26-31)
U.G.Jørgensen, Naturens Verden about the origin or the Earth's oceans (NV, vol.85, nr.2, p2-13),
U.G.Jørgensen, "Where does the elements come from?", Geologisk Museums udstillingskatalog, 2006.
Haack, H., Jørgensen, U. G., Andersen, A., Bizzarro, M., Buchwald, V. F. (2006). Solsystemet - fra altings oprindelse til livets opståen. Geoviden, (3), 2-19.
Haack, H, Jørgensen, UG, Andersen, A, Bizzarro, M, Buchwald, VF 2006, 'Solsystemets opståen.' Geologisk Nyt, no. 5, pp. 10-18.
U.G.Jørgensen, Kvant about the Deep Impact collision with Comet Tempel (vol.16 nr.3, 2005, p.11,12,36),
U.G.Jørgensen, Aktuel Astronomi about exoplanets (AA, 2004 nr 2, p.16-19) "Exoplanetjagten,
U.G.Jørgensen, Kvant about the formation of solar systems (vol.15 nr.3, 2004, p.8-14), "Er Solsystemet almindeligt blandt solsystemer?"


Science administrative involvement:

I am at present head of the astronomy area ("områdeleder" in Danish) of the Niels Bohr Institute, and head of our group for astrophysics and planetary science (in Danish astrofysik og planet forskning ).

I'm in charge of the operation of the Danish 1.54m telescope at La Silla, I lead the exoplanet part of the international SONG network of small robotic telescopes, and organize the MiNDSTEp microlensing search for exoplanets.

I participated in the creation of the Centre of Excelence, StarPlan, for understanding the role of our own solar system relative to other planetary systems in our Galaxy, and also in the formation of the Nordic Astrobiology Network.

I was a member of ESO's OPC for a number of years during the late 1990'ies, and later member of ESO's user's committee. Since 2011 I have been the Danish scientific member of the ESO Council. Two of the most interesting issues we are discussing in Council during these years is ESO's conscruction of the world's largest optical telescope, the almost 40 meter mirror European ELT telescope, and the transformation of ESO from a European to a global organisation for astronomy.


In the process of being updated, August 2014 by uffegj@nbi.dk.