This week on HST

HST Programs: February 20 - February 26, 2017

Selected highlights

GO 14610: A Legacy Imagign Survey of M33

M33, the Triangulum Galaxy (Subaru imaging)

Messier 33, or the Triangulum galaxy, is the smallest of the three spiral galaaxies in the Local Group. Lying at a distance of ~800 kpc from the Milky Way, the system may be a satellite of the Andromeda spiral, and certainly appears to have experienced past interactions. With a mass less than half that of the Milky Way, the galaxy has a small, distinct bulge, no bar and extensive star formation regions forming spiral structure. The proximity to the Milky Way means that Hubble can resolve individual stars, albeit limited to relatively high luminosities. The present program aims to build on that capability by mapping aproximately one-third of the system. Wide Field Camnera 3 and the Advanced Camera for Surveys will be used in parallel to image 54 fields, obtaining multi-band data from the near-UV (F275W filter) through the U, B and I bands (F336W, F475W, F814W) to the near-infarred (F110W and F160W). Those data will enable investigations of the initial mass function for luminous stars; trace the detailed star formation and recent history as a function of location within the galaxy; map the dust distribution; and allow for the detection of star clusters. This dataset will complement the extensive survey of the Andromeda spiral conducted via the PHAT survey.

GO 14633: A SNAP UV Spectroscopic Study of Star-Planet Interactions

SOHO image of an extremely strong solar flare

Stellar activity, whether through flares and coronal mass ejections, has the potential to affect the ability of life to evolve and survive on otherwise habitable planets in stellar systems. High energy radiation can lead to significant mutations, and particle ejections can actually strip the atmospheres of unfortunate planets. Previous HST programs have focused on low mass M dwarfs, the most populous stars in the galaxy, and systems where the habitable zone lies close to the parent star, with a correspondingly higher vulnerability. Those observations suggest evidence for interactions between the stellar transition region and the planets, with a correlation between the presence of high temperature emission lines (N V, C IV, Si IV) and the planetary mass and orbit i.e. suggestive of planetary interactions driving conditions in the stellar corona. The present SNAP program expand obsevations to higher-mass K dwarfs and solar-type G dwarfs that are known to harbour exoplanets, searching for similar correlations. The Cosmic Origins Spectrograph will be used to obtain UV spectra (1150-1450 Angstroms), providing a broad sampling of the range of activity levels among these dwarfs.

GO 14753: Supernova 1987A at 30 years

Evolution of a supernova remnant

SN1987A, in the Large Magellanic Cloud, is (as far as we know) the nearest supernova to the Sun since Kepler's supernova of 1604. While its eruption, in January 1987, predated HST's launch by over 3 years, the remnant has been a regular observational target since the installation of COSTAR at the first servicing mission. Those high resolution observations have revealed the development, and evolution, of extensive, intricate structures as the blast wave from SN1987A encounters the surrounding interstellar medium. In particular, a striking circum-remnant ring has developed, with numerous hot spots stimulated by the fastest moving debris. Over the past few cycles, the hotspots are fusing as the shock fully enters the ring, and photons from these regions are exciting previously hidden gas outside the ring, illuminating mass lost from the progenitor before the explosion. The inner debris are now well resolved, and clearly aspherical. By now, the blast wave has passed the inner ring, which is starting to fade, and is interacting with more distant materials. The present program will use the Cosmic Origins Spectrograph and the Space Telescope Imaging Spectrograph to obtain ultraviolet and optical spectra of the ejecta and the ring, probing the composition and enabling detailed modelling of nucleosynthesis. Overall, these observations provide crucial insight into the earliest stages of formation of a supernova remnant.

GO 14767: The Panchromatic Comparative Exoplanetary Treasury Program

Artist's impression of the GJ 1214 system

The first exoplanet, 51 Peg b, was discovered through radial velocity measurements in 1995. 51 Pegb was followed by a trickle, and then a flood of other discoveries, as astronomers realised that there were other solar systems radically different from our own, where "hot jupiters" led to short-period, high-amplitude velocity variations. Then, in 1999, came the inevitable discovery that one of those hot jupiters. HD 209458b, was in an orbit aligned with our line of sight to the star, resulting in transits. Since that date, the number of known transiting exoplanet systems has grown to more than 100 from ground-based observations, most detected through wide-field photometric surveys, while the high-sensitivity data provided by Kepler has added a further 1000+ confirmed systems and ~2000 additional candidates. Transiting systems not only provide an accurate measure of the planetary radius (at least relative to the parent star), they also provide us with an opportunity to probe the atmospheric composition through spectroscopy during the transit. Hubble has made significant inroads in this area, while Spitzer has contributed measurements of planetary emissivity through observations during and after eclipse. The James Webb Space Telescope has the capability to revolutionise our knowledge in this field through highly sensitiive observations at near and mid-infra red wavelengths. The present program aims to lay the foundation for those programs by using Hubble to compile multiwavelength (UV to near-IR) spectroscopic observations of 20 exoplanets. The targets are all gas giants, ranging from super-jovian masses to neptunian masses. The observations will be obtained with the Space Telescope Imaging Spectrograph and the near-infrared grisms on Wide Field Camera 3.