Abt H.A.,Kitt Peak National Observatory
Publications of the Astronomical Society of the Pacific | Year: 2017
The Am, or “Metallic-line,” stars have too strong line strengths of the iron peak elements for their temperatures and too weak He, Ca, etc. Michaud showed that the A4-F2 V stars, which occur in the same area of the main sequence as the Am stars, have radiative zones below their photospheres where diffusion acts to push metals upward into the photospheres by radiation pressure and lets Ca, etc. sink downward, but only if the stars are slow rotators. Slow rotation can be caused by the formation of disks or by tidal interactions in binaries. The Am stars are rich in binaries with P < 100 days; the rapidly rotation A4-F2 V stars have no such binaries. The special peculiarities do not occur in stars above the luminosity class V stars, except among the ρ Puppis stars, so the radiative zones must disappear and the atmospheres become well mixed with the interiors. The suggestion that the ρ Puppis stars are the descendents of the Am stars fails because there are too few ρ Puppis stars by a factor of about 100. Then by searching for binaries among evolved stars I conclude that the Am stars plus A4-F2 V normal stars evolve into A7-F9 IV stars and then into F2-F9 (or later) III stars with normal abundances. © 2017. The Astronomical Society of the Pacific. All rights reserved.
Abt H.A.,Kitt Peak National Observatory
Publications of the Astronomical Society of the Pacific | Year: 2017
I explore whether small or large teams produce the most important astronomical results, on average, using citation counts as our metric. I present evidence that citation counts indicate the importance of papers. For the 1343 papers published in A&A, ApJ, and MNRAS in 2012 January-February, I considered 4.5 years worth of citations. In each journal, there are larger citation counts for papers from large teams than from small teams by a factor of about 2. To check whether the results from 2012 were unusual, I collected data from 2013 for A&A and found it to be the same as that for 2012. Could the preponderance of papers by large teams be due to self-citations (i.e., citing and cited papers sharing one or more authors)? To answer this, I looked at 136 papers with one to 266 authors and discovered a linear relation that ranges from a 12.7% self-citation rate for single-author papers to a 45.9% selfcitation rate for papers with 100 authors. Correcting for these factors is not enough to explain the predominance of the papers with large teams. Then I computed citations per author. While large teams average more citations than small ones by a factor of 2, individuals on small teams average more citations than individuals on large teams by a factor of 6. The papers by large teams often have far more data, but those by small teams tend to discuss basic physical processes. © 2017. The Astronomical Society of the Pacific. All rights reserved.
News Article | May 3, 2017
PHOENIX--(BUSINESS WIRE)--Senate Bill 1114, sponsored by Sen. Sonny Borrelli and Lamar Advertising and recently signed by Gov. Doug Ducey, allows electronic billboards within a 40-mile radius of Bullhead City in western Arizona. Working with the Arizona Astronomy Consortium, the Arizona Technology Council was successful in negotiating an amendment with Sen. Borrelli and Lamar Advertising that helped protect Arizona’s famed dark skies while still accomplishing Lamar’s economic development goals in Mohave County. The Council worked for an amendment which limits the number of billboards to 35, caps the level of illumination to 200 nits in the newly approved area, and restricts the areas in which the billboards will be permitted. With potential statewide implications, the amendment includes legislative intent language that encourages the advertising industry to try to limit light pollution and to use state-of-the-art technology to further mitigate the impact of the light from the electronic billboards. “The language of this bill allows Mohave County to have economic development in the form of electronic billboards but still helps protect our existing observatories, as well as potential future sites,” said Steven G. Zylstra, president and CEO of the Arizona Technology Council. “Because they are among the top-rated dark sky areas in the world, professional astronomers flock to Northern Arizona and Tucson, second to only the star-filled skies from Mauna Kea in Hawaii, which is now built out to capacity.” A study published a decade ago showed the industry had an economic impact of $250 million annually -- not including the synergistic and strong optics sector -- and has been on a sustained path of growth since. The University of Arizona’s astronomy program alone has brought in over $100 million in sponsored research support every year for the last 12 years. That figure does not include the substantial NASA awards to the UA Lunar and Planetary Lab (OSIRIS-REX) or to the Arizona State University’s School of Earth and Space Exploration. “We’re pleased with the amended language in SB 1114 and thankful for the extensive work done by the Arizona Technology Council and Arizona Astronomy Consortium,” said Jeffrey Hall, director of the Lowell Observatory. “Artificial light at night is a threat to astronomical research, and it is crucial that we continue to protect the dark skies vital to Arizona's thriving astronomy industry." On the strength of its still-dark skies, Kitt Peak National Observatory outside of Tucson recently was awarded major new research projects, representing investments of tens of millions of dollars by the National Science Foundation, the Department of Energy and NASA. All these economic drivers are dependent on the state’s public commitment to protect Arizona’s valuable asset of dark skies. For more information on the Arizona Technology Council and its Public Policy Committee, visit www.aztechcouncil.org. The Arizona Technology Council is Arizona’s premier trade association for science and technology companies. Recognized as having a diverse professional business community, Council members work towards furthering the advancement of technology in Arizona through leadership, education, legislation and social action. The Arizona Technology Council offers numerous events, educational forums and business conferences that bring together leaders, managers, employees and visionaries to make an impact on the technology industry. These interactions contribute to the Council’s culture of growing member businesses and transforming technology in Arizona. To become a member or to learn more about the Arizona Technology Council, please visit http://www.aztechcouncil.org.
News Article | February 2, 2016
Using this discovery, they developed a procedure to find new infrared candidate blazars. However, analysis of these findings revealed that a piece of the puzzle was still missing: The conclusive identification of these astronomical powerhouses can only be obtained through observations of their visible light in tiny wavelength intervals, which astronomers call the optical spectrum. So at the end of 2011, Massaro and D'Abrusco assembled an international team of experts and started a large observational campaign to validate the nature of the largest possible sample of candidate blazars selected with their methods through spectroscopy. Recently, the last paper of a series of six has been accepted for publication. Previous reports appeared in the Astrophysical Journal, the Astronomical Journal and Astronomy and Astrophysics. The findings discussed in these papers represent the final results of meticulous work that has contributed key pieces to the puzzle represented by this family of strange sources. Blazars, one of the largest known classes of gamma-ray sources, are characterized as highly energetic emissions arising from a jets pointing toward the Earth, and which originate from rapidly spinning supermassive black holes in the centers of giant elliptical galaxies. The radiation from these jets is generated by particles accelerated to velocities very close to the speed of light that emit over the whole electromagnetic spectrum, from radio frequencies up to the highest energies ever detected, comparable to those released by thousands of supernovae exploding simultaneously. These powerful emissions make blazars the masters of the extragalactic gamma-ray sky. Discovering the astronomical sources observed at lower energies that can be associated to gamma-ray sources has recently attracted significant interest. Scientists hope that understanding the connection between well-known classes of objects and blazars will reveal something completely unexpected about the universe and its evolution—including, possibly, the true nature of dark matter, an elusive particle that has so far escaped detection and whose existence can only be deduced by its gravitational influence on visible matter. The Fermi Gamma-ray Space Telescope, an international collaboration between Italy, France, Japan, Sweden and the USA, has helped astronomers map the high-energy sky with unprecedented resolution and depth since 2008. Although Fermi has already significantly improved our knowledge of the number and characteristics of the most energetic sources in the local universe, about one-third of the gamma-ray sources detected by Fermi are still of unknown origin. The team of scientists coordinated by Massaro and D'Abrusco attempts to change that. "Our observations represent a major improvement of our knowledge on the demographics of the unidentified gamma-ray sources and gamma-ray blazars. In the near future, the outcome of our long-term project will allow us to put new more stringent constraints on the nature, abundance and behavior of the dark matter that permeates and drives the evolution of the Universe," said Francesco Massaro. "When we discovered that the infrared emission of Fermi blazars follows a specific pattern, our first idea was to apply our findings to the search of new infrared sources that could be responsible of the emission associated to the unidentified gamma-ray sources. While our method turned out to be very effective at selecting potential candidates, we could only confirm their nature by obtaining their optical spectra. Thus, we started a large project to verify the nature of the largest available sample of candidate blazars selected with our method." said D'Abrusco. "We collected spectra in observatories located all around the planet. After five years and tens of observing nights spent working with telescopes in Arizona (Kitt Peak National Observatory and Multiple Mirror Telescope), California (Palomar Observatory), Chile (Southern Astrophysical Research Telescope and Magellan), the Canary Islands (Telescopio Nazionale Galileo and William Herschel Telescope) and Mexico (National Astronomical Observatory in Sa Pedro Martir and Guillermo Haro Observatory), we recently reached the milestone of 200 confirmed gamma-ray blazars among completely unknown blazars and sources whose nature was uncertain before our observational campaign." The project has also produced other unexpected results. Two members of the team coordinated by Massaro and D'Abrusco have discovered a type of transitional blazar whose spectral continuum changes significantly over the time, and two blazars lacking a radio counterpart, which is a rarity even among the rarest class of extragalactic sources. These efforts were led by two Ph.D. students, Nuria Alvarez-Crespo at the University of Turin (Italy) and Federica Ricci at University of Roma Tre (Italy), who reduced and analyzed the spectra of several candidate blazars, exploiting the rare opportunity of working the night shifts at remote telescopes. More information: leggi l'articolo Identification of the Infrared Non-thermal Emission in Blazars di F. Massaro, R. D'Abrusco, M. Ajello, J. E. Grindlay, Howard A. Smith, The Astrophysical Journal, 2011. adsabs.harvard.edu/abs/2011ApJ...740L..48M leggi l'articolo The WISE Blazar-like Radio-loud Sources: An All-sky Catalog of Candidate gamma-ray Blazars di R. D'Abrusco, F. Massaro, A. Paggi, H. A. Smith, N. Masetti, M. Landoni, G. Tosti, The Astrophysical Journal Supplement, 2014. adsabs.harvard.edu/abs/2014ApJS..215...14D leggi l'articolo Optical Spectroscopic Observations of gamma-Ray Blazar Candidates. III. The 2013/2014 Campaign in the Southern Hemisphere di M. Landoni, F. Massaro, A. Paggi, R. D'Abrusco, D. Milisavljevic, N. Masetti, H. A. Smith, G. Tosti, L. Chomiuk, J. Strader, C. C. Cheung, The Astronomical Journal, 2015. adsabs.harvard.edu/abs/2015AJ....149..163L leggi l'articolo Refining the Associations of the Fermi Large Area Telescope Source Catalogs di F. Massaro, R. D'Abrusco, M. Landoni, A. Paggi, N. Masetti, M. Giroletti, H. Otí-Floranes, V. Chavushyan, E. Jiménez-Bailón, V. Patiño-Álvarez, S. W. Digel, H. A. Smith, A. Howard, G. Tosti, The Astrophysical Journal Supplement Series, 2015. adsabs.harvard.edu/abs/2015ApJS..217....2M
News Article | January 6, 2016
Using NASA's Chandra X-ray observatory, astronomers have discovered evidence of powerful blasts generated by a giant black hole. The black hole's epic "burp", which may have been triggered by the interaction of the black hole's host galaxy and a larger spiral companion, could shed light on one of the mysteries of galactic core. Astronomers have discovered that stars rarely form in the center of a galaxy, where a giant black hole often lies, and they do not know why. A black hole found at the center of the NGC 5195, appears to hold the answer with evidence of huge X-ray blast that may have swept away star-forming dust from the center of the dwarf galaxy. Study researcher Eric Schlegel, from The University of Texas in San Antonio, and colleagues used data from Chandra X-ray Observatory to investigate NGC 5195. The telescope was specially designed to detect X-ray emission from hot regions of the universe. The small galaxy is merging with a larger spiral galaxy NGC 5194, also called "The Whirlpool," with both lying in the Messier 51 galaxy system located about 26 million light-years away from Earth. Schlegel and colleagues detected two arcs of X-ray emission near the center of NGC 5195. The researchers said that the arcs represent remnants of two large blasts when the black hole belched material outward into the galaxy. The activity could have had big impact on the galaxy as the "burp" may have swept the dust-forming gas away from its center. View from the 0.9-meter optical telescope of the Kitt Peak National Observatory also revealed a thin region of cool hydrogen gas emission just outside of the outer X-ray arc. This indicates that the hotter gas that emits X-ray has likely snow-plowed the hydrogen gas from the galaxy's center. Schlegel said that this behavior would have likely occurred very often in the early universe, which changed the course of galaxies' evolution. The researchers said that the outburst of the giant black hole could be attributed to the interaction of the two galaxies that caused gas to be funneled in. The phenomenon provides evidence that black holes do not just "eat" stars and gas as they are more popularly known. They also appear to burp after meal. Study researcher Marie Machacek, from the Harvard-Smithsonian Center for Astrophysics said it is likely that the phenomenon known as "feedback" prevents galaxies from becoming too big. "But at the same time, it can be responsible for how some stars form. This shows that black holes can create, not just destroy," Machacek said. Results of the study were presented this month at the 227th meeting of the American Astronomical Society Kissimmee, Florida and published in the Nov. 10 issue of the Astrophysical Journal.
News Article | March 7, 2016
Arizona is in the midst of a struggle between light and dark. The state is home to a flourishing billboard industry which brightens up a vast network of freeways, but it is also a haven for astronomers who embrace the region's wide stretches of dark, desert sky and mountain peaks to gaze at the stars. The friction between these two industries is intensified as state lawmakers proposed a new bill that would expand the area in Arizona where electronic billboards are plastered along interstates and highways. Dark-sky advocates, however, argue that the bill would be detrimental to the state's astronomy industry. Glaring electronic billboards are prohibited in most of Arizona, except in Interstate 8 and 10 in Phoenix and the rest of the city, because of a compromise between advertisers and astronomers in 2012. The compromise was designed to prevent light pollution near observatories. If lawmakers proceed with the new bill, it would lift the ban in parts of La Paz County and in most of Mohave County. Timothy La Sota, spokesperson for Lamar Advertising who lobbies for the bill, said it is a matter of fairness for cities, and that if the state wants to generate revenues, cities should have the same ability as others when it comes to the electronic billboards. "Other cities and towns in Arizona [which] do that are in a similar situation -- they're not anywhere near an observatory," said La Sota. Lowell Observatory Director Jeffrey Hall acknowledges that the area is far from major observatories, but the new bill backtracks on the 2012 compromise and could have long-term effects. "The signal [this] sends is that Arizona is willing to — bit by bit — chip away at the dark-sky protection that keeps the astronomy industry viable," said Hall. Aside from Lowell Observatory in Flagstaff, Arizona contains Kitt Peak National Observatory and Mount Graham National Observatory. Hall and other astronomers take advantage of Arizona's dark night sky for research, stargazing, GPS monitoring and national defense purposes. He said the astronomy industry was worth $1.3 billion in capital investments in 2008 and spends $250 million yearly. Under the 2012 compromise, the dark-sky corridor is protected from electronic signs, streetlights and other sources of excessive artificial light, which are often perpetrators of light pollution. Hall and his colleagues are concerned that light from the billboard signs could affect the sensitive technologies they use to detect celestial bodies. Still, La Sota said advocates have nothing to worry about. "People aren't going to put these billboards out on an untraveled country road. It doesn't make any commercial sense," added La Sota. The House of Representatives has already passed the bill on a 32-26 vote last March 3, and it has now moved to Senate.
News Article | March 21, 2016
Since the 1990s, scientists have been aware that for the past several billion years, the universe has been expanding at an accelerated rate. They have further hypothesized that some form of invisible energy must be responsible for this, one which makes up 68.3% of the mass-energy of the observable universe. While there is no direct evidence that this "dark energy" exists, plenty of indirect evidence has been obtained by observing the large-scale mass density of the universe and the rate at which is expanding. But in the coming years, scientists hope to develop technologies and methods that will allow them to see exactly how dark energy has influenced the development of the universe. One such effort comes from the U.S. Department of Energy's Lawrence Berkeley National Lab, where scientists are working to develop an instrument that will create a comprehensive 3D map of a third of the universe so that its growth history can be tracked. Known as the Dark Energy Spectroscopic Instrument (DESI), this project plans to start with the present day, pinpointing the locations of galaxies in the universe, and then work backwards into the past. DESI officially kicked off with the recent delivery of two new and improved lenses to the Mayall Telescope at the Kitt Peak National Observatory in Arizona. The first of six such upgrades, these two new lenses – Corrector Lens 1 and Corrector Lens 4 (C1 and C4) – have been in production since early 2015. Measuring 1 meter in diameter and weighing 201.395 kg (444 pounds) and 236.775 kg (522 pounds), respectively, these lenses are scheduled to undergo a final antireflective coating before being integrated into the Mayall telescope's new steel corrector barrel. Each of these lenses comes equipped with 5000 optical fibers, similar to kind of cables used for high-speed data traffic (i.e. internet and telecommunications). They will give the 4-meter telescope a very wide field of view and be able to detect the light coming from 5000 galaxies at a time. This light will then be directed to the 30 cameras and spectrographs that are connected to the Mayall telescope, which the science team will then measure to gauge its redshift. For many years, the Berkeley Lab has been measuring the redshift of distant galaxies – the ratio of the wavelength that is seen to the wavelength the light had when it left the galaxy – to gauge their distances from our Solar System. However, since light will stretch exactly the way the universe stretches, these measurements have also been giving the Berkeley scientists an idea of how the universe is expanding. Once the entire DESI package is assembled – which is expected to happen by 2018 – it will begin collecting spectrographic information on a total of 35 million distant galaxies and quasars. This information will then be used to construct the largest 3D map of the universe, one that spans 10 billion light years. This will allow DESI scientists to not only survey the large-scale structure of the universe, but also look back in time and see how the universe changed over the past 10 billion years. However, redshift alone can only provide astronomers with relative distances. In order to create the 3D map with a genuine sense of scale, the DESI scientists will also be relying on baryon acoustic oscillations – which are periodic fluctuations in the density of the visible baryonic matter of the universe. Together, these measurements of the changing distance between galaxies could show us exactly how dark matter influences cosmic expansion. DESI is undeniably the next wave of innovation when it comes to how we observe the universe, combing high-performance optics with computer-assisted analysis. And when the map is finally complete, scientists may begin to see exactly how this mysterious energy that permeates our universe has influenced its expansion and evolution. Another step on the long, winding road from theory to knowing!
Abt H.A.,Kitt Peak National Observatory
Astronomical Journal | Year: 2012
I scanned the six major astronomical journals of 2008 for all 1589 papers that are based on new data obtained from ground-based optical/IR telescopes worldwide. Then I collected data on numbers of papers, citations to them in 3+ years, the most-cited papers, and annual operating costs. These data are assigned to four groups by telescope aperture. For instance, while the papers from telescopes with an aperture >7m average 1.29 more citations than those with an aperture of 2 to <4m, this represents a small return for a factor of four difference in operating costs. Among the 17 papers that have received ≥100 citations in 3+ years, only half come from the large (>7m) telescopes. I wonder why the large telescopes do so relatively poorly and suggest possible reasons. I also found that papers based on archival data, such as the Sloan Digital Sky Survey, produce 10.6% as many papers and 20.6% as many citations as those based on new data. Also, the 577.2 papers based on radio data produced 36.3% as many papers and 33.6% as many citations as the 1589 papers based on optical/IR telescopes. © 2012. The American Astronomical Society. All rights reserved.
Abt H.A.,Kitt Peak National Observatory
Scientometrics | Year: 2012
The Hirsch h-index is widely used to measure a researcher's major publications. It has the advantage of being easy to compute. However, it increases steeply with time and therefore does not allow a comparison of young and mature researchers. We find that if the h-index is divided by the number of decades since publication of the researcher's first paper, the result is statistically constant with age. Then the resulting index can be compared for young and old researchers. Its accuracy is the same as that of the h-index and is as easy to compute as the h-index. © 2011 Akadémiai Kiadó, Budapest, Hungary.
News Article | November 18, 2016
A precise map requires that DESI itself be built and assembled with micrometer precision. Fermilab, a Department of Energy national laboratory, is contributing a key piece of the instrument: a large, barrel-shaped device that will hold optical lenses to collect the light from millions of distant galaxies. The smallest deviation in lens alignment could lead to the instrument being permanently out-of-focus. Every piece of the barrel must be perfectly placed, so the Fermilab team is currently taking every measure to ensure its precise assembly. The process involves a special machine, meticulous handling and a healthy dose of patience. The lens-holding device is a roughly 8-foot-long and 4-foot-wide segmented cylinder—about the size of a small elevator. Once the hulking steel barrel is complete, it will be installed at the Mayall four-meter telescope at the Kitt Peak National Observatory, southwest of Tucson, Arizona. The lenses will collect the light reflected from the telescope's mirror and focus it into 5,000 optical fibers, through which the light is transported to special detectors, called spectrographs. With the help of 10 such spectrographs, scientists can measure the distance of the galaxies. In May, a team of specialists at Fermilab began assembling the barrel's five segments carefully, checking that each nut and bolt was perfectly situated. But a nuts-and-bolts-level fit isn't enough. To achieve the precision scientists are aiming for, the DESI barrel and its inner structure must be assembled accurately to within an incredibly tight 20 micrometers. That's one 10th of the thickness of a sheet of paper. To achieve the required fit, the team has been making small, critical adjustments to the assembled barrel. The barrel adjustments take place in a vacant area the size of a small bedroom. Four tall pillars – nearly seven feet high – stand at the corners of the space. Above their heads, a rail, similar to train tracks, connects the tops of the two pillars on one side. A second rail connects the other two. A moveable carriage track spans the gap – like a high bridge spans a river – connecting the two rails. The carriage itself glides along the track. The team guides the carriage so that it stops just above the barrel. The carriage carries a mechanical arm that points towards the floor. It can rotate in all directions in the space within the pillars. At the end of the arm is a highly sensitive and precise sensor, fixed to an articulating motorized probe. The arm with the sensor comes to life: It reaches down to the barrel and starts feeling for its surfaces. It searches for specific points on the barrel – a corner, an edge, another significant surface marker. When it finds them, it measures the coordinates in the designated space. Very carefully and with tiny movements, it moves over the whole surface of the barrel, measuring up, down and around the surface. As it does, it records the measurement data and saves it for further analysis. Jorge Montes, one of the team members, strategically places markers on the barrel's surface to assist their alignment efforts. After making the measurement, the scientists return the barrel to an outside area. There they disassemble it, realign all the parts, relying on the previously placed markers. They then reassemble it. With great care they bring the once more fully assembled barrel into the empty space and measure anew the precision of their assembly. Comparing their performance with their previous assembly, they learn which pieces, if any, are misaligned—even slightly—and where they improved the alignment. The precise, slow-moving measuring machine that points out the misalignments is called a coordinate measuring machine, or CMM. The group making these point-by-point measurements, led by Fermilab engineering physicist Michael Roman, uses it to ensure the DESI barrel's perfect assembly. With the help of the CMM, they repeat the whole procedure of assembly, measurement and disassembly again and again, always comparing their performance against previous tries. When they reach their alignment within 10 micrometers—about a 10th the width of a human hair—in a certain number of tries, they are satisfied. "From early on we knew that the barrel needed high-precision measurements for the assembly and that it would be too large for any of the CMMs at Fermilab to perform such measurements," Roman said. "In strong support of DESI, Fermilab bought a machine for the dedicated measurements on the barrel," said scientist Gaston Gutierrez, who is one of the DESI project leads at Fermilab. To ensure that the CMM's measurements are as precise as they need to be, the CMM is set up in an air-conditioned room, where scientists monitor and control the temperature 24 hours a day. Materials expand when they get warm, affecting the accuracy of CMM's measurements. So scientists worked out the right control settings for the environmental control system to ensure that the temperature never varied more than one degree from 20 degrees Celsius. Even the eventual effect of heavy weights on the DESI barrel, including the lenses, can be measured with the new CMM. Scientists place the DESI barrel in the machine and measure it, then add test weights on its sides and remeasure the barrel. The team can see how the barrel shrinks or bends, if at all, and determine whether the lenses will hold steady when the telescope is in motion. The Fermilab team expects to finish all CMM measurements by early 2017. Then they will disassemble the DESI barrel and send it to the University College London. In London, their colleagues will install the lenses in the support structures. Once the lenses are installed, the barrel will start its journey to its future home in Arizona. Measuring the expansion of the universe Scientists have discovered that our universe is growing bigger and bigger—without any end in sight. Like raisins in a rising loaf of bread, the universe's galaxies are being pushed apart from each other. From previous measurements, scientists have a kind of cosmic ruler, a standard length that goes back to the universe's early beginning. Using this ruler together with the high-precision DESI map, scientists will be able to tell how far galaxies have moved apart and how much our universe has grown throughout its history. "With the DESI experiment, we want to follow the growing steps of our universe," Gutierrez said. "We start from today and go backwards in time to measure how much the universe has expanded since its early days. The fabrication, assembly and operation of DESI are small but highly important steps toward precisely understanding the universe. Explore further: New lenses to help in the hunt for dark energy