The Center for Astrophysics | Harvard & Smithsonian

The Center for Astrophysics | Harvard & Smithsonian

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Steven Saar

Center for Astrophysics

Astrophysicist

Steven Saar

ssaar@cfa.harvard.edu

About

I am a solar/stellar physicist in the Solar/Stellar X-ray group(SSXG) of the High Energy division at SAO. I work to measure magnetic fields in solar-like stars, to better understand how they are generated and evolve, and their many effects on stellar evolution, surface structure, and atmospheric heating. I'm also exploring how stellar magnetic activity complicates the detection of exoplanets, and ways around these problems. I also study magnetic activity on our Sun (the the most nearby, well-resolved, and solar-like star of all!). Besides being the most important star, the Sun is an very helpful comparison/contrast point to keep stellar speculations well grounded.

Telescopes and Instruments

Chandra

The Chandra X-ray Observatory is NASA’s flagship X-ray observatory, providing essential data on everything from the environment surrounding newborn stars to the emissions from hot plasma inside galaxy clusters. The Smithsonian Astrophysical Observatory (SAO), as part of the Center for Astrophysics | Harvard & Smithsonian, manages Chandra’s day-to-day operations, providing spacecraft control, observation planning, and data processing for astronomers. Chandra is one of NASA’s orbiting Great Observatories, along with the Hubble.

Visit the Chandra Website

Einstein Observatory

NASA’s Einstein Observatory was the first X-ray space telescope designed to produce images of astronomical X-ray sources. The spacecraft operated from 1978 through 1981, providing important observations of pulsars, supernova remnants, supermassive black holes in other galaxies, and many more, paving the way for NASA’s Chandra X-ray Observatory. The X-ray telescope was designed by researchers at the Center for Astrophysics | Harvard & Smithsonian.

High Accuracy Radial Velocity Planet Searcher-North (HARPS-N)

Measuring the mass of a distant exoplanet requires tracking the changes in light of the host star as the planet’s gravity tugs it slightly — a delicate process. The High Accuracy Radial velocity Planet Searcher for the Northern hemisphere (HARPS-N) is an instrument designed for that purpose. HARPS-N is installed on the Telescopio Nazionale Galileo at the Roque de los Muchachos Observatory on the island of La Palma in the Canary Islands. The instrument provides valuable follow-up observations for the smaller exoplanets identified by NASA’s Kepler/K2 space telescope and other observatories. Astronomers at the Center for Astrophysics | Harvard & Smithsonian are part of the international collaboration operating the instrument. Using the high quality data from HARPS-N, astronomers hope to measure the masses of Earth-like worlds to sufficient accuracy to determine how much these planets resemble ours.

Visit the HARPS-N Website

Hinode

The Sun is the closest star to Earth, and the single most important influence on the worlds of the Solar System in terms of the light and particles it emits. Studying the Sun, in other words, helps us understand the habitability of Earth, but also other stars elsewhere in the universe. One important solar observatory is the Japanese Aerospace Exploration Agency’s Hinode spacecraft, which carries three powerful instruments to study the Sun in X-rays, visible light, and ultraviolet light. Center for Astrophysics | Harvard & Smithsonian engineers collaborated in the development of the X-ray Telescope for the spacecraft. Hinode has been observing the Sun continuously since its launch in 2006, providing important day-by-day information about our host star’s activity.

Visit the Hinode/XRT Website

Interface Region Imaging Spectrograph (IRIS)

The Sun’s surface is incandescently hot, but its outer atmosphere — the corona — is far hotter, for reasons astronomers don’t fully understand. NASA’s Interface Region Imaging Spectrograph (IRIS) is an orbiting observatory designed to study the mysterious transitional part of the Sun’s lower atmosphere, where the heating of the material flowing into the corona takes place. Understanding the heating process may help predict solar storms as well. Scientists and engineers from the Center for Astrophysics | Harvard & Smithsonian contributed to the telescope for IRIS. In addition, CfA researchers participate in telescope operations, and provide scientific support and analysis for the observatory’s work.

Visit the IRIS Website

Kepler/K2

Since the early 1990s, astronomers have identified thousands of planets orbiting other stars. Most of those identifications have come thanks to one observatory: NASA’s Kepler space telescope. Until it lost its ability to point, Kepler observed a region of the sky containing about 150,000 stars with potential planets, monitoring them for the slight decrease in light caused by planets crossing in front of the star. After the spacecraft’s pointing control failed, the mission was renamed K2, and it continued to hunt for exoplanets as it tumbled slowly, with its field of view drifting slowly across the sky. The mission finally ended in 2018, though the data it produced continues to provide astronomers with valuable information about planets in our galactic neighborhood. Astronomers from the Center for Astrophysics | Harvard & Smithsonian were responsible for the preparation of the catalog for potentially interesting stars, and have participated extensively in follow-up observations of Kepler planetary discoveries.

Visit the Kepler/K2 Website

MMT Observatory

The MMT Observatory is the premier visible-light and infrared telescope jointly managed by the Smithsonian Astrophysical Observatory, part of the Center for Astrophysics | Harvard & Smithsonian, and the University of Arizona. Located at the Fred Lawrence Whipple Observatory (FLWO) in southern Arizona, this 6.5-meter (21 foot) telescope is used to study objects across the field of astronomy, from the Solar System to distant galaxies. The MMT has provided a testbed for new telescope technologies developed by scientists and engineers at the CfA and the University of Arizona.

Visit the MMT Website

SOFIA (Stratospheric Observatory for Infrared Astronomy)

Earth’s atmosphere protects us from harmful radiation, but it also blocks a lot of light useful for astronomy. For that reason, NASA and the German Aerospace Center (DLR) built the Stratospheric Observatory for Infrared Astronomy (SOFIA) to fly aboard a modified commercial aircraft capable of flying above 99% of the light-blocking atmosphere. SOFIA is a powerful, general-purpose infrared observatory used to study the birth of new stars, planetary nebulas and supernova remnants, the atmospheres of Solar System objects, and many more. The American portion of SOFIA management is handled by the Universities Space Research Association (USRA), a private educational corporation consisting of over 100 institutions, including the Center for Astrophysics | Harvard & Smithsonian.

Visit the SOFIA Website

Solar and Heliospheric Observer (SOHO)

The Sun is the only star we can study in detail, providing us with the opportunity to observe stellar internal structure, magnetic fields, and atmosphere. Solar and Heliospheric Observer (SOHO), a space observatory jointly operated by NASA and the European Space Agency (ESA), has been one of the best sources for that knowledge. Originally designed to operate for two years, SOHO has provided daily data on the Sun for more than twenty years, making it one of the longest running space observatories. During that time, SOHO has monitored the Sun’s atmosphere, surface, and seismology, using a wide range of scientific instruments. Scientists and engineers at the Center for Astrophysics | Harvard & Smithsonian developed the instrument SOHO uses to measure the ultraviolet spectrum of the Sun.

Visit the SOHO/UVCS Website

Solar Dynamics Observatory (SDO)

The Sun is both life-giving and dangerous. Variations in the Sun’s light and wind have profound effects on Earth, while solar storms can wreak havoc on power and communications systems. NASA’s Solar Dynamics Observatory (SDO) is a spacecraft dedicated to studying these potentially dangerous variations, and the magnetic fields that drive them. Engineers at the Center for Astrophysics | Harvard & Smithsonian contributed to the design and construction of the four Atmospheric Imaging Array (AIA) telescopes. AIA is one of the three major experiments carried by SDO.

Visit the SDO Website

Transiting Exoplanet Survey Satellite (TESS)

Astronomers have discovered thousands of planets orbiting other stars. Extrapolating from that knowledge, the Milky Way alone is probably home to hundreds of billions of planets, many of which are likely rocky, Earth-like worlds. NASA’s Transiting Exoplanet Survey Satellite (TESS) is a space observatory designed to look for exoplanets in orbit around 200,000 nearby bright stars, with a particular interest in identifying small planets. Astronomers from the Center for Astrophysics | Harvard & Smithsonian are part of the scientific team to analyze TESS data, as well as performing follow-up observations. The relative closeness of worlds in the TESS survey will allow astronomers to even study some of their atmospheres, using the future Giant Magellan Telescope (GMT) and other observatories. TESS observational program is complementary to NASA’s long-running Kepler/K2 mission, and could identify as many as 20,000 new exoplanet orbiting a wide variety of star types.

Visit the TESS Website

Transition Region and Coronal Explorer (TRACE)

The Transition Region and Coronal Explorer (TRACE) was a space-based solar observatory which operated from 1998 through 2010. TRACE primarily observed in ultraviolet light to map the small-scale structure of the eruptions of gas on the Sun’s surface known as coronal loops, as well as the “transition region” where the Sun’s atmosphere increases in temperature dramatically. The telescope was a joint project of the Center for Astrophysics | Harvard & Smithsonian, NASA, and Lockheed Martin. The long duration of the mission enabled TRACE to be the second space-based solar observatory to monitor an entire sunspot cycle, which provided valuable information on how the Sun’s magnetic field affects its atmosphere.