Monday, March 18, 2019

Mapping Stars with PEPSI

The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) in Arizona released its first image of the surface magnetic field of another star. In a paper in the European journal Astronomy & Astrophysics, the PEPSI team presents a so-called Zeeman-Doppler-Image (ZDI) of the surface of the magnetically active star II Pegasi. 

A special technique allows astronomers to resolve the surfaces of faraway stars. Those are otherwise only seen as point sources, even in the largest telescopes and interferometers. This technique, referred to as Doppler imaging (DI) or Doppler tomography, requires a high-resolution spectrograph, usually a large telescope, lots of observing time, and nifty analysis software.

But PEPSI can go a major step further. Because its two polarimeters also feed polarized light to the spectrograph, PEPSI captures the otherwise hidden profile deformation due to the Zeeman-effect. (splitting and polarization of spectral lines due to an external magnetic field). Combined with the rotational Doppler-effect it allows the reconstruction of the star’s surface magnetic field geometry. 

Stellar environment of the star II Pegasi. Shown is the magnetic-field extrapolation out to 2.2 stellar radii. Open field lines are depicted in colour (magenta: negative polarity, green: positive polarity, closed loops are in white.) Credit: AIP

Wednesday, April 25, 2018

Stellar Dust Survey Paves Way for Exoplanet Missions

Credits: NASA/JPL-Caltech
Using the Large Binocular Telescope Interferometer, or LBTI, on Mount Graham in Arizona, the HOSTS survey determines the brightness of warm dust floating in the orbital planes of other stars (called exozodiacal dust). In particular, HOSTS has studied dust in nearby stars’ habitable zones, where liquid water could exist on the surface of a planet. The LBTI is five to 10 times more sensitive than the previous telescope capable of detecting exozodiacal dust, the Keck Interferometer Nuller.

Among the findings detailed in the new paper, the HOSTS scientists report that a majority of Sun-like stars in their survey do not possess high levels of dust -- good news for future efforts to study potentially-habitable planets around those stars. A final report on the full HOSTS survey results is expected early next year.

More information about the new findings from HOSTS and the search for Earthlike planets beyond our solar system is available in this news release from the University of Arizona.

The full NASA Press Release is here.

Wednesday, January 10, 2018

First PEPSI Data Release

The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) in Arizona released its first batch of high-spectral resolution data to the scientific community. In a series of three papers in the European journal Astronomy & Astrophysics, the PEPSI team presents a new spectral atlas of the Sun, a total of 48 atlases of bright benchmark stars, and a detailed analysis of the chemical abundances of the 10-billion year old planet-system host Kepler-444.

Spectral atlases are the fingerprints of stars and give insights into almost all of their physical properties like temperature, pressure, velocities and chemical composition. The first paper contains a new spectral atlas of the Sun and proves for the first time that a night-telescope instrument can reach a quality comparable to a specialized solar instrument. All solar and stellar spectra were taken with an unprecedented spectral resolution of λ/Δλ=250,000, a resolution equivalent to a 1/100th of the diameter of a hydrogen atom (λ being the wavelength and Δλ the smallest measurable separation of two wavelengths) and cover the entire optical and near-infrared light (from 383 to 914nm).
The fingerprint of a star.
Example from the new PEPSI atlases:
the nearby planet-host star epsilon Eridani.
Click here for a full resolution pdf version.

For the Sun several spectral time series with up to 300 individual spectra per day were pre-analyzed and are also provided to the community. "These data recover the well-known solar 5-minute oscillation at a peak of 3 mHz (5.5min) from the disk-averaged light with a radial-velocity amplitude of only 47 cm/s, an incredibly small velocity from a stellar point of view", says Prof. Strassmeier, PEPSI principal investigator and director of the Cosmic Magnetic Field branch at the Leibniz Institute for Astrophysics Potsdam (AIP). The new atlas was also used to re-determine the abundance of Lithium in the Sun with very high precision. "Lithium is a key element for the nucleosynthesis in the universe and is also a tracer of mixing processes inside stars", explains Dr. Matthias Steffen, one of the project scientists. Three-dimensional dynamic model atmospheres and a full statistical treatment of the spectral properties of the lithium atom were applied to determine the solar abundance.

The 48 stellar atlases in the second paper include the northern Gaia benchmark stars as well as other Morgan-Keenan standard stars. Spectra of these targets were not available at the given resolution and signal-to-noise ratio (S/N) before. The latter quantity represents the photon noise relative to the signal strength from the star and thus the quality of the spectra. Previously available S/N for work on astrophysical parameters was typically several hundred at a spectral resolution λ/Δλ of at most 100,000. "PEPSI and the LBT provide S/N of several thousand at on average three times higher spectral resolution", says Ilya Ilyin, PEPSI’s project scientist. "With such numbers we have now the typical daytime solar-like spectrum quality available also for bright stars at night time", adds Strassmeier.

The PEPSI instrument at LBT. Credit: AIP
Finally, in the third paper, the star "Kepler-444", hosting five sub-terrestrial planets, was confirmed to be 10.5 billion years old, more than twice the age of our Sun and just a little bit younger than the universe as a whole. The star is also found being poor on metals. The chemical abundance pattern from the PEPSI spectrum indicates an unusually small iron-core mass fraction of 24% for its planets if star and planets were formed together. For comparison, terrestrial planets in the solar system have typically a 30% iron-core mass fraction. “This indicates that planets around metal-poor host stars are less dense than rocky planets of comparable size around more metal-rich host stars like the Sun”, explains Claude “Trey” Mack, project scientist for the Kepler-444 observation.

Science contacts:
    Prof. Dr. Klaus G. Strassmeier, 0331-7499-223,    
    Dr. Ilya Ilyin, 0331-7499-269,
    Dr. Christian Veillet (Large Binocular Telescope Observatory), +1 (520) 621-5286,

Media contact:
    Dr. Janine Fohlmeister, 0331-7499-803,

More information on PEPSI and the LBT:

Thursday, January 4, 2018

'SHARKs' will Help LBT Hunt for Exoplanets

Two new instruments will give the Large Binocular Telescope a set of sharper eyes capable of studying planets outside our solar system in greater detail.

A pair of new-generation instruments to be mounted on the world's largest optical telescope, the Large Binocular Telescope, or LBT, located on top of Mount Graham in Arizona, will turn the telescope into a formidable hunter of extrasolar planets. Named SHARK (short for System for coronagraphy with High order Adaptive optics from R to K band), the instruments will enable astronomers to obtain direct images of exoplanets, including very faint ones, by more effectively blocking the otherwise overpowering light from their host stars.

INAF, the Italian National Institute for Astrophysics, is leading the international consortium that will build the instruments and will also manage their scientific use.

SHARK recently has received the official green light from the LBT board, and the two instruments are expected to become fully operational by the end of 2019. SHARK consists of a pair of instruments working synergistically in visible light (SHARK-VIS) and in the near infrared (SHARK-NIR). These will be operated in parallel, taking advantage of the two big 8.4-meter mirrors of the LBT, thus making it the first telescope in the world capable of observing exoplanets simultaneously over such a wide range of wavelengths.

The main problem exoplanet hunters face when studying exoplanets is the extreme contrast between the planets' faintness in comparison to their host stars' light, explains Christian Veillet, director of the Large Binocular Telescope, which is managed by the University of Arizona.

To be able to study candidates for potentially Earth-like planets, for example, astronomers need more sophisticated instruments to tease out the signal from the noise.

The "SHARKs" will take full advantage of the outstanding adaptive optics system mounted on the LBT, which was also developed by INAF. This system corrects in real time the image distortions induced by the atmospheric turbulence to deliver final frames that are characterized by a sharpness and quality of detail better than those obtainable with the Hubble Space Telescope.

"LBT’s Adaptive Optics is currently undergoing a makeover offering even better performance, which will be fully utilized by SHARK to bring the LBT to the forefront of what is possible in this arena," Veillet says. "We are preparing the path to doing unprecedented science on the next generation of telescopes, such as the Giant Magellan Telescope, an LBT on steroids with seven 8.4-meter mirrors on the same mount instead of two."

"With SHARK, we will observe exoplanets at unprecedented angular resolution and contrast, so that we will be able to go closer to their host stars than what has been achieved up to now with direct imaging," says Valentina D’Orazi of the INAF-Osservatorio Astronomico di Padova, instrument scientist for SHARK-NIR. "This will be possible thanks to the use of coronagraphy, which blocks out the light from the central star and highly improves the contrast in the region around the source, thus allowing us to detect the planetary objects we want to study, which otherwise would remain hidden in the star light.”  


 "With this great combination, we will finally be able to reveal many exoplanets around stars in our galactic neighborhood and better characterize their properties, by also using images in optical light taken for the first time in the northern hemisphere," adds Fernando Pedichini of the INAF-Osservatorio Astronomico di Roma and principal investigator of SHARK-VIS.


With SHARK, it will be possible to directly image gaseous giants in the outer regions of exoplanetary systems, thus obtaining pieces of information about the architecture of such systems that are complementary to those provided by techniques purely focused on detection. Such techniques include observing the gravitational tug unseen planets exert on their host star, or the minuscule dip in a star's brightness when a planet passes in front of it.

"These observations are key to understanding the formation mechanisms of planetary systems," says Simone Antoniucci of the INAF-Osservatorio Astronomico di Roma, instrument scientist of SHARK-VIS. "Moreover, one of the unique features of SHARK will be the capability to directly observe the formation process of giant planets around very young stars."

"Thanks to the outstanding sensitivity of the LBT adaptive optics system, SHARK-NIR, used in parallel with SHARK-VIS and the LBTI LMIRCAM instrument, will allow us to study not only exoplanets, but also astrophysical phenomena," says Jacopo Farinato, astronomer at the INAF-Osservatorio Astronomico di Padova and principal investigator of SHARK-NIR. "For instance, we will be able to study with formidable accuracy disks and jets of young stars, gas envelopes around evolved stars, asteroids and minor bodies of the solar system and even the brightest extragalactic sources such as active galactic nuclei."

"While these two SHARKs are built as instruments to be operated by the teams who built them, they will be open to the whole LBT community," Veillet adds. "Both teams have garnered an impressive scientific collaboration, covering the wide range of potential scientific programs as well as the diverse partnership on which LBT is built."

Each SHARK will be installed on one side of the LBT Interferometer (LBTI), the green structure seen in the middle of the picture between the two main mirrors of LBT. 
The SHARK consortium is led by INAF, and the partners for the NIR channel are the Steward Observatory in Tucson (University of Arizona), the Max Planck institute of Heidelberg (Germany) and the Institut de Planétologie et d’Astrophysique of Grenoble. The Italian institutes involved in the instrument construction are the Observatories of Padova, Roma, Arcetri, Milano, Trieste and the Physics and Astronomy department of the University of Padova.

The Large Binocular Telescope (LBT) is an international collaboration of the University of Arizona, Italy's National Institute for Astrophysics (INAF), Germany's LBT Beteiligungsgesellschaft, The Ohio State University, the Tucson–based Research Corporation representing the University of Minnesota, the University of Virginia, and the University of Notre Dame.  INAF contributes 25 percent of the LBT costs (construction and management) and owns one fourth of the telescope and of the same share of observing time.

Contact Information

At INAF, Italy:
Marco Galliani Chief Press Officer - INAF (Italian National Institute for Astrophysics)
office phone +39 06 355 33 390  mobile +39 335 17 78 428

At LBTO (Tucson, AZ)
Christian Veillet -  - 1 (520) 349 4576

The INAF Press Release (in Italian) is here.

Tuesday, October 17, 2017

Earth Quasi Satellite (469219) 2016 HO3 an asteroid, not Space Junk

At the 49th Annual Division for Planetary Sciences Meeting in Provo, Utah, astronomers led by Vishnu Reddy at the University of Arizona confirm true nature of one of Earth's companions on its journey around the sun.  

Was it a burned-out rocket booster, tumbling along a peculiar near-earth orbit around the sun, and only occasionally getting close enough to be studied with even the largest telescopes?

Not at all, as it turns out. While, based on previous observations, most astronomers had strongly suspected that object (469219) 2016 HO3 was an ordinary asteroid and not space junk, it took a team of astronomers led by Vishnu Reddy, assistant professor at the Lunar and Planetary Laboratory, University of Arizona, working with one of the world’s largest telescopes, the Large Binocular Telescope (LBT), on Mt. Graham in Southeastern Arizona, to learn the true nature of this near-Earth object.

2016 HO3 is a small near-Earth object (NEO) measuring no more than 100 meters (330 feet) across that, while orbiting the Sun, also appears to circle around the Earth as a "quasi-satellite." Only five quasi-satellites have been discovered so far, but 2016 HO3 is the most stable of them. The provenance of this object is unknown. On timescales of a few centuries, 2016 HO3 remains within 38-100 lunar distances from us.

2016 HO3 is seen at the top left corner of this animation made of ten 2mn long exposures in I band using MODS1 on the left side of LBT - The telescope is tracking the moving asteroid, so background stars (and even a couple of galaxies) are trailed.  Credit LBTO

“While HO3 is close to the Earth, its small size – possibly not larger than 100 feet – makes it challenging target to study, said Reddy. “Our observations show that the HO3 rotates once every 28 minutes and is made of materials similar to asteroids." 

Soon after its discovery in 2016, astronomers were not sure where this object came from, but in a recent presentation at the annual Division for Planetary Sciences Conference of the American Astronomical Society in Provo, Utah, Reddy and his colleagues show that Earth’s new traveling buddy is an asteroid and not space junk. The new observations confirm that 2016 HO3 is a natural object of similar provenance to other small NEOs that zip by the Earth each month. 

"In an effort to constrain its rotation period and surface composition, we observed 2016 HO3 on April 14 and 18 with the Large Binocular Telescope and the Discovery Channel Telescope," Reddy said. "The derived rotation period and the spectrum of emitted light are not uncommon amongst small NEOs, suggesting that 2016 HO3 is a natural object of similar provenance to other small NEOs."

Light curve of 2016 HO3 showing the 28m rotation period of the asteroid
(MODS on LBT on Apr 14, and LMI on DCT on Apr 18)

In their presentation, "Ground-based Characterization of Earth Quasi Satellite (469219) 2016 HO3," Reddy and his co-authors, Olga Kuhn, Audrey Thirouin, Al Conrad, Renu Malhotra, Juan Sanchez, and Christian Veillet, point out that the light reflected off the surface of 2016 HO3 is similar to meteorites we have on Earth. 

One way to visualize HO3's orbit is by picturing a hula hoop dancer – the sun in this analogy – twirling two hoops around the hips at the same time, ever so slightly out of sync. While it orbits the sun, the object makes yearly loops (link to ) around the Earth. As a result, the object appears to orbit the Earth, but it is not gravitationally bound to our planet.

"Of the near-Earth objects we know of, these types of objects would be the easiest to reach, so they could potentially make suitable targets for exploration," said Veillet, director of the LBT Observatory. "With its binocular arrangement of two 8.4-meter mirrors, coupled with a very efficient pair of imagers and spectrographs like MODS, LBT is ideally suited to the characterization of these Earth's companions." 

NASA Near-Earth Object Observations Program Grant NNX17AJ19G (PI: Reddy) funded parts of this work. 

# # #
PIO Contact: Daniel W. Stolte +1 520-621-4402
Science Contact at LPL: Vishnu Reddy
Science contact at LBTO: Christian Veillet

"Ground-based Characterization of Earth Quasi Satellite (469219) 2016 HO3," Vishnu Reddy, Olga Kuhn, Audrey Thirouin, Al Conrad, Renu Malhotra, Juan A. Sanchez, Christian Veillet. 49th Annual Division for Planetary Sciences Meeting - Tuesday, October 17th, 2017. 204.07.

Thursday, October 12, 2017

The LBT gets polarized: First light for the PEPSI polarimeters

Thanks to a cleverly designed "two-in-one" instrument attached to the world's most powerful telescope, astronomers can extract more clues about the properties of distant stars or exoplanets than previously possible. 

Developed at the Leibniz-Institute for Astrophysics in Potsdam, Germany, the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) saw first light on April 1, 2015, after being successfully installed at the Large Binocular Telescope Observatory (LBTO) in Arizona, USA. 

Once both of PEPSI's polarimeters were mounted in the focus points of each of the LBT's two 8.4-meter mirrors  in early September 2017, the telescope was pointed to the star gamma Equ and polarized light was received. From these spectra astronomers can, for example, deduce the geometry and strength of magnetic fields on the surfaces of distant stars, or study the reflected light from the atmospheres of potentially habitable exoplanets.

The DX (right side) polarimeter on LBT
A polarimeter separates starlight according to its oscillation planes. It is complementary to a spectrograph that, like a prism, separates light according to its oscillation frequencies (or color). The two combined, polarimeter and spectrograph, added to a powerful telescope, enable astronomers to obtain spectra in polarized light. This in turn allows the characterization of the full wave-front of the incoming stellar light and extract details of its radiation physics that otherwise remain hidden. 

A series of integrations in circularly and linearly polarized light was obtained when the telescope was pointed to the magnetic reference star Gamma Equulei, or gamma Equ, a double star located about 118 light-years from Earth. These spectra have a spectral resolution of R=120,000, that means they can resolve two wavelengths only five hundredths of a hydrogen atom’s diameter apart. They cover two large wavelength regions in the visible light simultaneously, and have an unprecedented signal-to-noise ratio. Because the two polarimeters for each of LBT's "eyes" are identical and modular in design, circular and linear polarizations were obtained simultaneously. 

 First polarimetric spectrum from PEPSI. The target is the bright magnetic A9VpSrCrEu star gamma Equ. The black line is the PEPSI spectrum and the red line is, for comparison, the HARPS-Pol  spectrum. From top to bottom: the magnetic null spectrum enlarged by a factor five, the normalized linear Stokes component U/Ic enlarged by a factor 5, the normalized linear Stokes component Q/Ic  enlarged by a factor 5, the normalized circular Stokes component V/Ic, and the normalized integral light I/Ic. Because the two polarimeters for each of LBT's "eyes" are identical and modular in design, circular and linear polarizations were obtained simultaneously. 

The gamma Equ test also included a so-called null spectrum, which is obtained by swapping the observation sequence in the two fibers. Ideally, it would give zero polarization and be independent of wavelength. Any residual polarization would be due to instrumental effects.  

“The null spectrum for PEPSI shows an extraordinary low degree of polarization noise caused by the instrument,"  says its principal investigator, Prof. Dr. Klaus Strassmeier, Research Branch Director at AIP  and a professor of astronomy at the University of Potsdam. "Compared with the best spectropolarimeters currently available at other telescopes, it's probably better by a factor of ten." 

“Eventually, the PEPSI polarimeters will enable stellar magnetic field measurements with extremely high precision," adds PEPSI’s project scientist Dr. Ilya Ilyin. 

The SX (left side) polarimeter on LBT
For Dr. Christian Veillet, LBTO Director, “In the 8-10m class telescope select club, PEPSI was already a unique instrument, thanks to its resolution coupled to two 8.4-m mirrors simultaneously available. The addition of a polarimeter on each of LBT’s eyes gives LBTO yet another unique capability. It comes as a precious complement to interferometry, which gives LBT's two eyes the imaging resolution of a 23-m telescope."

The PEPSI instrument is available to all LBT partners.

The press release at AIP is here.

More information about PEPSI here.

Science contacts:
Prof. Dr. Klaus G. Strassmeier (Principal Investigator), +49 331-7499 223,
Dr. Ilya Ilyin (project scientist), +49 331-7499 269,

Media contacts:
Katrin Albaum (AIP), +49 331-7499 803,
Christian Veillet (Large Binocular Telescope Observatory),+1 520-349-4576,

The key areas of research at the Leibniz Institute for Astrophysics Potsdam (AIP) are cosmic magnetic fields and extragalactic astrophysics. A considerable part of the institute's efforts aim at the development of research technology in the fields of spectroscopy, robotic telescopes, and e-science. The AIP is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory of Potsdam founded in 1874. The latter was the world's first observatory to emphasize explicitly the research area of astrophysics. The AIP has been a member of the Leibniz Association since 1992.

The LBT is an international collaboration among institutions in the United States, Italy and Germany. LBT Corporation partners are: The University of Arizona on behalf of the Arizona Board of Regents; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, The Leibniz Institute for Astrophysics Potsdam, and Heidelberg University; The Ohio State University, and The Research Corporation, on behalf of The University of Notre Dame, University of Minnesota and University of Virginia.

Friday, September 8, 2017

LBT snags first glimpse of OSIRIS-REx since launch

OSIRIS-REx is  a NASA spacecraft traveling to a near-Earth asteroid called Bennu to bring a small sample back to Earth for study. The mission launched Sept. 8, 2016, from Cape Canaveral Air Force Station. As planned, the spacecraft will reach Bennu in 2018 and return a sample to Earth in 2023.

The spacecraft is currently approaching Earth for its gravity assist maneuver, which will change its trajectory and set it on course to rendez-vous Bennu. Its closest approach to Earth is scheduled for 12:52 p.m. EDT on Friday, Sept. 22.

The Large Binocular Telescope Observatory (LBTO) used the LBCs (Large Binocular Cameras), a pair of wide-field cameras at the prime focus of each of its two 8.4m mirrors, to image the field around the predicted position of the spacecraft on the night of September 1.

The animation above (three images - LBCB - 300s exp. time - V filter) centered on OSIRIS-REx (red square).  2017 September 2 at around 11:00 UTC. The spacecraft was 11-million kilometers away from Earth at the time of the observation. The spacecraft was  28% illuminated with a magnitude V~25.

On that night, LBTO was back on sky after a long period of shutdown which started on June 15 due to the Frye fire, followed by its seasonal monsoon shutdown (Jul 10 - Aug 31). OSIRIS-REx was an excellent target of opportunity at the beginning of a 12-night period dedicated to a full restart of the facility. A good way to come back to observing after 2.5 months of closed dome!

Thanks go to V. Reddy and A. Conrad for proposing the target, B. Rothberg, O. Kuhn, J. Hill and S. Allanson for observing, C. Veillet and C. Hergenrother for the data reduction, and the whole LBTO staff for a great shutdown work!