State of the Hubble Observatory

Rachel Osten,

Now in its 26th year of operations, Hubble is still going strong, producing science that continues to challenge and expand our understanding of the universe. From predicting supernovae, to finding the most distant spectroscopically confirmed galaxy, to detecting water-vapor plumes above the surface of Europa, the breadth of Hubble’s science is vast and continues to grow. After 26 years and over 142,000 orbits of the Earth, Hubble is a healthy, mature observatory, and all subsystems are operating in a nominal status; extrapolations predict mission continuation beyond 2020. In this Newsletter article, we provide a brief “State of the Observatory” overview of recent activities.

At this time, Hubble operations are running smoothly. There has been a remarkable absence of safemode entries and instrument hang-ups. The planning and scheduling team has been especially successful in crafting efficient long-range plans, with an average of 86.5 orbits per week in the first 30 weeks of Cycle 23, compared with an average of 84.0 orbits per week in Cycles 17–22.

Hubble 2020

In Spring 2015, a call for white papers was issued to solicit community input on initiatives that will enhance significantly Hubble’s scientific legacy over the next five years of observations. The Hubble 2020 vision was described in the 2015 vol. 32, issue 01 Newsletter article by Ken Sembach, “Towards a 2020 Vision for the Hubble Space Telescope.”

Three main recommendations are being implemented as a result of this community input. The first is a continuation of the enormously successful UV initiative, started in Cycle 21, and the second is the initiation of a James Webb Space Telescope Preparatory Initiative, starting with the current Cycle 24. Read more about these in the following subsections. The third outcome of the white papers was a recommendation that the Institute should provide an opportunity for the community to submit very large proposals—similar to the enormously successful Multi-Cycle Treasury Program of Cycles 18–20—with a particular emphasis on science topics that are unique to Hubble, including UV science. Starting in Cycle 24, these very large programs (more than 350 orbits) will be incorporated in the regular proposal review, with explicit instructions to the TAC, and may be subsidized from Director’s Discretionary time. The orbit allocation will be shared between Cycles 24 and 25. Early indications after the Cycle 24 proposal deadline are that the community has responded with overwhelming enthusiasm to this opportunity to propose for larger projects.

Hubble, by any definition a truly Great Observatory, remains at the forefront of observational astrophysics more than 25 years after its launch in 1990, thanks to the optical quality of the telescope, the excellent pointing performance of the spacecraft, the suite of instruments, the quality of the data and archive, and the experienced operations teams. The mission technical objectives reflect the goal to maximize science in Hubble’s remaining years. This goal, for a five-year horizon, should not jeopardize longer-term operations and future scientific productivity, especially since Hubble continues to operate near peak performance nearly seven years after Servicing Mission 4.

In the fall of 2015, the GSFC Flight Dynamics Facility analysis indicated reentry of the spacecraft no earlier than 2028, and most likely in 2036. With the exception of the gyroscopes, and the expected depletion rate of the COS FUV detector simply due to use, the spacecraft subsystems and instrument health and performance status have not significantly changed in the last several years. The methodology employed in the 2013 NASA Engineering and Safety Center (NESC) report, and recently updated for the NASA Senior Review of operating missions (see below), established the same familiar high confidence that Hubble’s instruments and subsystems will remain operable through the next five-year period. The NESC analysis shows that there is a >98% probability of having WFC3 and COS available in 2020. The Hubble team continues to pay close attention to the effects of use and on-orbit aging as we strive to optimize the long-term use and performance of the observatory.

UV Initiative

The UV Initiative, in place since Cycle 21, recognizes the unique capability that Hubble has in accessing the ultraviolet (UV) portion of the electromagnetic spectrum (wavelengths less than 3200 Angstroms), and encourages proposals that seek to utilize these resources. Nearly all categories of proposals (Small, Medium, Large, and Treasury GO proposals, as well as Regular Archival, Legacy Archival, and Theory proposals) are eligible for the UV Initiative. Telescope Allocation Committees (TACs) have been encouraged to devote at least 40% of their orbit allocation to UV-specific science; these levels are advisory, not quotas, and all accepted Hubble proposals must independently meet the high bar of outstanding scientific quality. In Cycles 21 through 23, a total of 305 accepted observing programs have made use of the UV Initiative. The science programs being conducted under the UV Initiative span almost all science categories (see Figure 1). The UV Initiative continues in Cycle 24 and beyond. Bibliographical information for accepted UV Initiative programs can be found at this link.

Figure 1: Graphs summarizing UV initiative.

The LEGUS (Legacy ExtraGalactic UV Survey; a GO Cycle 21 Large Program) is a conspicuous example of the breakthrough science enabled by the UV initiative (Figure 2). LEGUS ( is focused on providing a critical missing piece in the star-formation puzzle: connecting star formation at the parsec-sized scale of individual stars, stellar clusters, and associations to kiloparsec-scale patterns of star formation in galaxy disks. Observations with LEGUS—five-band imaging in NUV, U, B, V and I filters, for 50 nearby galaxies with WFC3 and ACS imaging in the Hubble archive—enable reconstruction of the recent star-formation histories (SFH) at accuracies of about 10 Myr, and break the age-extinction degeneracies on small scales.

Figure 2: Observations of the nearby spiral galaxy NGC 6503 in optical and UV light trace the spatial and temporal evolution of star formation within galaxies, from the pc-sized scales of stars to the kpc-sized scales of star formation.

Hubble’s spatial resolution and wide-band coverage display clustering of star formation in these galaxies, revealing hierarchical structuring of star formation (Elmegreen et al. 2014; Gouliermos et al. 2015). The self-similarity of structures of star formation down to parsec scales is consistent with turbulence playing an important role in triggering star formation (Elmegreen et al. 2014). In addition, LEGUS observations determine the recent star-formation histories of stars and clusters and their impact on the UV star-formation rate calibrations. Calzetti et al. (2015) determined from extraordinarily well-sampled spectral energy distributions of young massive clusters that star formation in one nearby dwarf starburst galaxy has become more concentrated over the last 15 Myr. The wide range of galactic environments and broad wavelength coverage enable a host of additional science; LEGUS observations have already been exploited for studies of supernova progenitors and their environments (Van Dyk et al. 2015) and investigations of the role and fate of star clusters in relation to the natal environment (Grasha et al. 2015).

Preparing for the James Webb Space Telescope

The anticipated launch of the James Webb Space Telescope in October 2018 will bring extensive photometric and spectroscopic capabilities spanning the 0.7–28 micron wavelength range. Some science programs to be undertaken by Webb may require or be enhanced by Hubble observations. The JWST Initiative, starting in Cycle 24 and recommended as a result of the Hubble 2020 initiative, provides an opportunity to obtain observations with Hubble that complement and enhance the scientific impact of Webb observations. Hubble has capabilities at UV and optical wavelengths that complement and extend Webb’s capabilities, and there are some science goals which may be achieved only with the combination of both Hubble and Webb observations. All GO programs are eligible for the JWST Initiative, but other proposal categories (SNAP, AR, Theory) are not. Proposals must be tackling science questions that can only addressed with a combination of Hubble and Webb observations. Proposals will be addressed on the science case of the joint program, even if there is a limited science return from the proposed Hubble data.

The nominal science planning timeline for Webb (described in Jason Kalirai’s article in the 2015, vol. 32, issue 02 Newsletter) has a JWST GO Cycle 1 proposal deadline in February 2018, with proposal selection taking place in May 2018. Astute Hubble observers will note the overlap with the traditional cycle for Hubble, which has a proposal deadline in early April, and Telescope Allocation Committee (TAC) meeting in early June. The Institute will host the TACs for both observatories; such a close conjunction would likely cause significant logistical hurdles, in addition to inducing community weariness about proposal submission and evaluation. Options are currently under consideration for alterations to the proposal submission and review schedules to forestall any issues with jointly operating two great observatories.

Cycle 23 Mid-Cycle Proposal Selection

The Cycle 23 Call for Proposals contained an additional new category of GO proposals that allows for a faster response to new discoveries than the annual proposal cycle allows. This expands upon the Director’s Discretionary Proposal category, which is generally limited to observations of time-critical events. Mid-cycle proposals provide the community with an opportunity to capitalize quickly on recent discoveries through short (≤5 orbit) proposals for observations of newly discovered astrophysically interesting objects. The proposed observing program needed to have minimal constraints in order to maximize scheduling flexibility and ensure ability to execute observations in the current cycle. Up to 200 orbits was available at each of two mid-cycle proposal deadlines.

The two solicitations had rolling submissions, with cutoffs of October 1, 2015 and January 31, 2016. Members of the community who have contributed to recent Hubble TAC reviews did the scientific review. A total of 13 programs involving 52 orbits was approved after the inaugural mid-cycle proposal selection cutoff in October, and a further 9 programs involving 34 orbits were approved after the second call. Proposals submitted after the January 31 cutoff were held over for consideration, along with proposals submitted for the Cycle 24 Call for Proposals. A listing of the approved programs from the mid-cycle call can be found in Table 1. This mid-cycle proposal selection is expected to continue in Cycle 24.

Table 1: Listing of Accepted Mid-cycle Proposals

Accepted Cycle 23 Mid-Cycle Proposals
Name Institution ESA Member Title
Zachory Berta-Thompson MIT Hydrogen Escape from an Earth-size Exoplanet: a Reconnaissance Study
Rychard Bouwens Universiteit Leiden yes Preparing for JWST through Constraints on the Bright End of the z ~ 9 LF from CANDELS
David Enrenreich Observatoire de Geneve yes Atmospheric Escape from the Closest Super-Earth
Thomas Evans University of Exeter yes Characterizing an Exteme Planet of the Verge of Tidal Disruption
Boris Gaensicke The University of Warwick yes AR Sco: The First White Dwarf Pulsar?
Frederick Hamann Univeristy of Florida A Remarkable New Transient Outflow in the Quasar PG 1411+442
David Jewitt UCLA Hubble Investigation of Active Asteroid 324P/La Sagra
Mercedes Lopez-Morales Smithsonian Institution Astrophysical Observatory Atmospheric Sodium and a Precise Radius for the Closest Super-Earth
Carlo Manara ESA-ESTEC yes The HST-ALMA connection: Measuring the FUV Spectrum of a Newly Discovered Transition Disk down to the H2 and CO Photodissociation Regime
Bruce McCollum Catholic University of America Identifying the Progentior of a New Red Transient
Ivana Orlitova Astronomical Institute, Academy of Sciences of CR Lyman Alpha Halo in a Confirmed Lyman Continuum Leaker
Jonathan Tan University of Florida Peering to the Heart of Massive Star Birth
Siyi Xu European Southern Observatory -- Germany yes A White Dwarf with an Actively Disintegrating Asteroid
Vincent Bourrier Observatoire de Geneve yes UV Exploration of two Earth-sized Planets with Temperate Atmospheres
J. Howk University of Notre Dame Pop III Material Found 6 Gyr after the Big Bang? COS Constraints on the Lowest-metallicity Gas at z < 1
David Jewitt UCLA Comet P/2010 V1 as a Natural Disintegration Laboratory
Andrew Newman Carnegie Institution of Washington Resolving the Stellar Populations, Structure, and Kinematics of the NIR-Brightest Lensed Galaxy at z = 2
Keith Noll NASA Goddard Space Flight Center Trojan Binary Candidate: A Slow-Rotating Mission Target
Renske Smit Durham University yes Identifying z > 12 galaxies with JWST: What Sources Produce Strong UV Emission Lines?
David Sobral Lancaster University yes The Gas-metallicity and the ISM of the Brightest Lyman-alpha Emitter at z = 6.6: Metal-free?
Jonathan Tan University of Florida Peering to the Heart of Massive Star Birth. II. Completion of the Eight-Source Pilot Survey
Michael Wong University of California- Berkeley A New Dark Vortex

Hubble at the AAS

A special session at the AAS Winter meeting in Kissimmee, FL entitled “Hubble Space Telescope: A Vision to 2020 and Beyond,” showcased recent developments aimed at giving new life to the instruments and science with Hubble. Topics addressed plans for the next several years of operations; to extend Hubble’s lifetime into the Webb era and remain a forefront observatory while doing so, by maximizing the scientific output with new observing modes, as well as accelerating the pace of discovery with catalogs and archive tools. The session was recorded, and may be viewed at the following site:

Talk titles and speakers in the special session were:

“Maximizing the Scientific Return and Legacy of the Hubble Space Telescope Mission,” Jennifer J. Wiseman (NASA/Goddard Space Flight Center)

Hubble Space Telescope: A Vision to 2020 and Beyond: The Hubble Source Catalog,” Louis-Gregory Strolger (STScI)

“High precision astrometry with HST/WFC3 Scanning mode: Parallaxes of two Galactic Cepheids,” Stefano Casertano (STScI); Adam G. Riess (JHU, STScI)

“The new European Hubble archive,” Guido De Marchi; Maria Arevalo; Bruno Merin (ESA)

“Near-infrared Grism Spectroscopy with the Wide Field Camera 3: Insights from the 3D-HST Survey,” Ivelina G. Momcheva (Yale University, STScI)

“The Ultraviolet Spectroscopic Legacy of HST,” Thomas R. Ayres (U. of Colorado)


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