Archive for direct imaging

Complex structure at sub-arcsecond resolution in the gas-rich debris disk HD 141569A

Posted in astronomy with tags , , , on June 6, 2016 by Tim Kendall

28396PerrotHD 141569A is a transition disk that is still gas-rich but contains significant amounts of dust. In a new paper using the SPHERE coronagraph on the ESO VLT, Perrot et al. reveal that the inner 100 astronomical units (au) contains a series of concentric ringlets at physical separation of 47 au, 64 au, and 93 au. The paper is “Discovery of concentric broken rings at sub-arcsec separations in the HD 141569A gas-rich, debris disk with VLT/SPHERE”, 2016, A&A 590, L7. From the abstract:

Transition disks correspond to a short stage between the young protoplanetary phase and older debris phase. Along this evolutionary sequence, the gas component disappears leaving room for a dust-dominated environment where already-formed planets signpost their gravitational perturbations. We endeavor to study the very inner region of the well-known and complex debris, but still gas-rich disk, around HD 141569A using the exquisite high-contrast capability of SPHERE at the VLT. Recent near-infrared (IR) images suggest a relatively depleted cavity within ~200 au, while former mid-IR data indicate the presence of dust at separations shorter than ~100 au. We obtained multi-wavelength images in the near-IR in J, H2, H3 and Ks-bands with the IRDIS camera and a 0.95–1.35 μm spectral data cube with the IFS. Data were acquired in pupil-tracking mode, thus allowing for angular differential imaging. We discovered several new structures inside 1′′, of which the most prominent is a bright ring with sharp edges (semi-major axis: 0.4′′) featuring a strong north-south brightness asymmetry. Other faint structures are also detected from 0.4′′ to 1′′ in the form of concentric ringlets and at least one spiral arm. Finally, the VISIR data at 8.6 μm suggests the presence of an additional dust population closer in. Besides, we do not detect companions more massive than 1–3 mass of Jupiter. The performance of SPHERE allows us to resolve the extended dust component, which was previously detected at thermal and visible wavelengths, into very complex patterns with strong asymmetries; the nature of these asymmetries remains to be understood. Scenarios involving shepherding by planets or dust-gas interactions will have to be tested against these observations.

VLT/SPHERE imaging of the circumbinary disk and massive exoplanet around HD 106906

Posted in astronomy with tags , , , , on October 28, 2015 by Tim Kendall

Planet-hunting SPHERE Images First Circumbinary Planet System wi

Image and text credit: ESO, A. M. Lagrange (Université Grenoble Alpes) Observations by ESO’s planet-finding instrument, SPHERE, a high-contrast adaptive optics system installed on the third Unit Telescope of ESO’s Very Large Telescope, have revealed the edge-on disc of gas and dust present around the binary star system HD 106906AB.

HD 106906AB is a double star located in the constellation of Crux (The Southern Cross). Astronomers had long suspected that this 13 million-year-old stellar duo was encircled by a debris disc, due to the system’s youth and characteristic radiation. However, this disc had remained unseen — until now. The system’s spectacular debris disc can be seen towards the lower left area of this image. It is surrounding both stars, hence its name of circumbinary disc. The stars themselves are hidden behind a mask which prevent their glare from blinding the instrument.These stars and the disc are also accompanied by an exoplanet, visible in the upper right, named HD 106906 b, which orbits around the binary star and its disc at a distance greater than any other exoplanet discovered to date — 650 times the average Earth–Sun distance, or nearly 97 billion kilometres. HD 106906 b has a mammoth mass of up to 11 times that of Jupiter, and a scorching surface temperature of 1500 degrees Celsius. Thanks to SPHERE, HD 106906AB has become the first binary star system to have both an exoplanet and a debris disc successfully imaged, providing astronomers with a unique opportunity to study the complex process of circumbinary planet formation.

HD_106906_b_imageImage: This is a discovery image of planet HD 106906 b in thermal infrared light from MagAO/Clio2, processed to remove the bright light from its host star, HD 106906 AB. The planet is more than 20 times farther away from its star than Neptune is from our Sun. This is one of the most extreme separations known and it may be more appropriate to consider HD 106906 b a low mass brown dwarf companion. (Image: Vanessa Bailey).

Direct imaging discovery of a companion to 51 Eridani

Posted in astronomy with tags , , on August 14, 2015 by Tim Kendall

51-eridani-b-discovery-image

Astronomers have found the smallest planet outside this solar system yet to be directly photographed by a telescope on Earth, a methane-shrouded gas giant much like a young Jupiter. The exoplanet 51 Eridani b orbits the ~20 Myr old F0 star 29.4±0.3 parsecs from Earth in a planetary system that may be much like Earth’s own solar system. The discovery could shed light on how our solar system formed, scientists added. Over the last 20 years, astronomers have confirmed the existence of more than 1,800 exoplanets, or alien planets around other stars. Many of these worlds are quite unlike any planets in Earth’s solar system. For example, so-called “hot Jupiters” are gas giants that orbit their host stars more closely than Mercury does the sun.  More than 1,000 of the exoplanets confirmed to date were discovered by NASA’s Kepler Space Telescope. Kepler indirectly finds planets by detecting a loss of starlight as a world passes in front of its star. However, this new planet was discovered using the Gemini Planet Imager, an instrument on the Gemini South telescope in Chile, which directly detects exoplanets by looking for light from the worlds themselves. “To detect planets, Kepler sees their shadow,” study lead author Bruce Macintosh, lead investigator on the Gemini Planet Imager and an astrophysicist at Stanford University in California, said in a statement. “The Gemini Planet Imager instead sees their glow, which we refer to as direct imaging.” The scientists detailed their findings online Aug. 13 in the journal Science. [via space.com] [Update: A step toward rewriting planet formation models]

VLT/SPHERE non-detection of the proposed brown dwarf in the V471 Tauri system

Posted in astronomy with tags , , , , on February 18, 2015 by Tim Kendall

Wide-field view of the sky around the unusual binary star V471 TImage and text credit: European Southern Observatory (ESO) science release. A tertiary brown dwarf companion in the V471 Tauri eclipsing binary system has been postulated since at least 2001. The star itself is centred in the above image. Detection of the brown dwarf as a residual in the fitted light curve of the eclipsing primary/secondary pair had been claimed in 2011 and indeed the presence of a fourth, planetary mass body hinted at. However the brown dwarf has not been found by a new instrument which should have been capable of easily detecting it, the SPHERE exoplanet imager at ESO/VLT. A link to the research paper itself is here (via ESO). From the science release:

The new SPHERE instrument on ESO’s Very Large Telescope has been used to search for a brown dwarf expected to be orbiting the unusual double star V471 Tauri. SPHERE has given astronomers the best look so far at the surroundings of this intriguing object and they found — nothing. The surprising absence of this confidently predicted brown dwarf means that the conventional explanation for the odd behaviour of V471 Tauri is wrong. This unexpected result is described in the first science paper based on observations from SPHERE. Some pairs of stars consist of two normal stars with slightly different masses. When the star of slightly higher mass ages and expands to become a red giant, material is transferred to other star and ends up surrounding both stars in a huge gaseous envelope. When this cloud disperses the two move closer together and form a very tight pair with one white dwarf, and one more normal star. [Such pairs are known as post common envelope binaries]. One such stellar pair is called V471 Tauri. It is a member of the Hyades star cluster in the constellation of Taurus and is estimated to be around 600 million years old and about 163 light-years from Earth. The two stars are very close and orbit each other every 12 hours. Twice per orbit one star passes in front of the other — which leads to regular changes in the brightness of the pair observed from Earth as they eclipse each other. A team of astronomers led by Adam Hardy (Universidad Valparaíso, Valparaíso, Chile) first used the ULTRACAM system on ESO’s New Technology Telescope to measure these brightness changes very precisely. The times of the eclipses were measured with an accuracy of better than two seconds — a big improvement on earlier measurements. The eclipse timings were not regular, but could be explained well by assuming that there was a brown dwarf orbiting both stars whose gravitational pull was disturbing the orbits of the stars. They also found hints that there might be a second small companion object. Up to now however, it has been impossible to actually image a faint brown dwarf so close to much brighter stars. But the power of the newly installed SPHERE instrument on ESO’s Very Large Telescope allowed the team to look for the first time exactly where the brown dwarf companion was expected to be. But they saw nothing, even though the very high quality images from SPHERE should have easily revealed it. The SPHERE images are so accurate that they would have been able to reveal a companion such as a brown dwarf that is 70 000 times fainter than the central star, and only 0.26 arcseconds away from it. The expected brown dwarf companion in this case was predicted to be much brighter.

From the paper abstract:

We report that an unprecedented contrast of [12.1 magnitudes (H band)] at a separation of 260 mas was achieved, but resulted in a non- detection. This implies that there is no brown dwarf present in the system unless it is three magnitudes fainter than predicted by evolutionary track models, and provides damaging evidence against the circumbinary interpretation of eclipse timing variations. In the case of V471 Tau, a more consistent explanation is offered with the Applegate mechanism, in which these variations are prescribed to changes in the quadrupole moment within the main-sequence star.

More (on a very different topic): The oldest stars in the universe formed 560 Myr after the Big Bang, 140 Myr later than previously thought (Scientific American). This new Planck result is important as it resolves certain difficulties which had arisen from the earlier date and also implies that the very first stars which formed (often called Population III stars) might be more easily detected in the future. This is one of the prime observational goals of the James Webb Space Telescope (JWST).

The HR 8799 system observed by the Gemini Planet Imager

Posted in astronomy with tags , , , on January 7, 2015 by Tim Kendall

geminiplanet

GPI imaging of the planetary system HR 8799 in the near-infrared K band, showing 3 of the 4 planets. (Planet b is outside the field of view shown here, off to the left.) These data were obtained on November 17, 2013 during the first week of operation of GPI and in relatively challenging weather conditions, but with GPI’s advanced adaptive optics system and coronagraph the planets can still be clearly seen and their spectra measured (below). Credit: Christian Marois (NRC Canada), Patrick Ingraham (Stanford University) and the GPI Team.

Stunning exoplanet images and spectra from the first year of science operations with the Gemini Planet Imager (GPI) were featured today in a press conference at the 225th meeting of the American Astronomical Society (AAS) in Seattle, Washington. The Gemini Planet Imager GPI is an advanced instrument designed to observe the environments close to bright stars to detect and study Jupiter-like exoplanets (planets around other stars) and see protostellar material (disk, rings) that might be lurking next to the star.

Marshall Perrin (Space Telescope Science Institute), one of the instrument’s team leaders, presented a pair of recent and promising results at the press conference. He revealed some of the most detailed images and spectra ever of the multiple planet system HR 8799. His presentation also included never-seen details in the dusty ring of the young star HR 4796A. “GPI’s advanced imaging capabilities have delivered exquisite images and data,” said Perrin. “These improved views are helping us piece together what’s going on around these stars, yet also posing many new questions.”

The GPI spectra obtained for two of the planetary members of the HR 8799 system presents a challenge for astronomers. GPI team member Patrick Ingraham (Stanford University), lead the paper on HR 8799. Ingraham reports that the shape of the spectra for the two planets differ more profoundly than expected based on their similar colors, indicating significant differences between the companions. “Current atmospheric models of exoplanets cannot fully explain the subtle differences in color that GPI has revealed. We infer that it may be differences in the coverage of the clouds or their composition.” Ingraham adds, “The fact that GPI was able to extract new knowledge from these planets on the first commissioning run in such a short amount of time, and in conditions that it was not even designed to work, is a real testament to how revolutionary GPI will be to the field of exoplanets.”

1-geminiplanet

GPI spectroscopy of planets c and d in the HR 8799 system. While earlier work showed that the planets have similar overall brightness and colors, these newly-measured spectra show surprisingly large differences. The spectrum of planet d increases smoothly from 1.9-2.2 microns while planet c’s spectrum shows a sharper kink upwards just beyond 2 microns. These new GPI results indicate that these similar-mass and equal-age planets nonetheless have significant differences in atmospheric properties, for instance more open spaces between patchy cloud cover on planet c versus uniform cloud cover on planet d, or perhaps differences in atmospheric chemistry. These data are helping refine and improve a new generation of atmospheric models to explain these effects. Credit: Patrick Ingraham (Stanford University), Mark Marley (NASA Ames), Didier Saumon (Los Alamos National Laboratory) and the GPI Team. Materials courtesy phys.org.

A wide co-moving companion to the young M3 star GU Piscium

Posted in astronomy with tags , , , on May 20, 2014 by Tim Kendall

GUPscb_GMOSiz_WIRCamJ_noinset

Image and text credit: Gemini Observatory

An international team led by Université de Montréal researchers has discovered and photographed a new planet 155 light years from our solar system. GU Psc b is around 2,000 times the Earth-Sun distance from its star, a record among exoplanets. Given this distance, it takes approximately 80,000 Earth years for GU Psc b to make a complete orbit around its star! The researchers also took advantage of the large distance between the planet and its star to obtain images. By comparing images obtained in different wavelengths (colours) from the OMM and CFHT, they were able to correctly detect the planet.

The paper is Marie-Eve Naud et al., (2014) ApJ 787, 5, doi:10.1088/0004-637X/787/1/5. From the abstract:

We present the discovery of a comoving planetary-mass companion ~42” (~2000 AU) from a young M3 star, GU Psc, a likely member of the young AB Doradus Moving Group (ABDMG). The companion was first identified via its distinctively red i – z color (>3.5) through a survey made with Gemini-S/GMOS. Follow-up Canada-France-Hawaii Telescope/WIRCam near-infrared (NIR) imaging, Gemini-N/GNIRS NIR spectroscopy and Wide-field Infrared Survey Explorer photometry indicate a spectral type of T3.5 ± 1 and reveal signs of low gravity which we attribute to youth. Keck/Adaptive Optics NIR observations did not resolve the companion as a binary. A comparison with atmosphere models indicates T eff = 1000-1100 K and log g = 4.5-5.0. Based on evolution models, this temperature corresponds to a mass of 9-13 M Jup for the age of ABDMG (70-130 Myr).

Exoplanet direct imaging from National Geographic. Update: a new caveat in exoplanet science: exomoons with atmospheres might mimic one atmosphere in chemical disequilibrium. (via pnas.org)

Direct imaging discovery of a planet around a young A8 star

Posted in astronomy with tags , , , , , , on June 3, 2013 by Tim Kendall

eso1324c
Image credit: ESO/Digitized Sky Survey 2. Acknowledgement: Davide De Martin
eso1324aA new, 4 – 5 Jupiter mass probable planet discovery has been reported today around the young (10 – 17 Myr) dusty A8 star HD 95086. The companion is detected in the L’ band at 3.8 microns (left, image courtesy ESO/J. Rameau) using the NACO adaptive optics instrument at the ESO VLT. The best detection has a signal-to-noise ratio of 9. The projected separation is 56 AU and the planet is still warm, with surface temperature is around 1000K. The model-dependent mass obtained means this companion is the lightest planet yet directly imaged. The star lies close to the galactic plane as can easily be seen in the main image of the field around HD 95086, but contamination of the detection by a background object is unlikely, and the planetary status of the companion is reinforced by a non-detection in the Ks band (2.18 microns). The astrometry confirms it is co-moving with the star. The paper is “Discovery of a probable 4-5 Jupiter-mass exoplanet to HD 95086 by direct-imaging”, J. Rameau et al., arXiv preprint [pdf], and is accepted to ApJ letters.

In another new development, NASA have shown that the closest red dwarf, Proxima Centauri, will pass close to two background stars in alignments in 2014 and again in 2016 (below) which will allow possible planets around Proxima to be detected by microlensing, as well as yielding an accurate mass measurement for the star itself:

Microlensing occurs when a foreground star passes close to our line of sight to a more distant background star. These images of the background star may be distorted, brightened and multiplied depending on the alignment between the foreground lens and the background source. These microlensing events, ranging from a few hours to a few days in duration, will enable astronomers to measure precisely the mass of this isolated red dwarf. Getting a precise determination of mass is critical to understanding a star’s temperature, diameter, intrinsic brightness, and longevity. Astronomers will measure the mass by examining images of each of the background stars to see how far the stars are offset from their real positions in the sky. The offsets are the result of Proxima Centauri’s gravitational field warping space. The degree of offset can be used to measure Proxima Centauri’s mass. The greater the offset, the greater the mass of Proxima Centauri. If the red dwarf has any planets, their gravitational fields will produce a second small position shift.

752970main_Hubble-RareStellarIMAGEp1322ay
Image credit: NASA, ESA, K. Sahu and J. Anderson (STScI), H. Bond (STScI and Pennsylvania State University), M. Dominik (University of St. Andrews), and Digitized Sky Survey (STScI/AURA/UKSTU/AAO). The scalloped appearance of the path of the star is due to the Earth’s orbital motion.

There is more to read on highly accurate astrometry and microlensing, as well as direct imaging, in a new article from Space Review on the specifications and exoplanet detection capabilities of WFIRST-2.4, while for those who prefer more conceptual reading, there is another article about loop quantum gravity and the resolution of black hole singularities. The paper under discussion is Gambini & Pullin, “Loop quantisation of the Schwarzschild black hole”, in Phys. Rev. Lett., (arXiv), the essential idea being that LQG can provide a mathematical description applicable to both black holes and the early Universe which is able to remove (resolve) the problematic singularity introduced by general relativity in both cases.