Observing with Street Lights

Observing with Street Lights
Dark sky sites not always necessary to see the Milky Way (This image was taken ouside of a B&B in Julian, CA)

Tuesday, January 9, 2018

Some summary comments from the American Astronomical Society 231st meeting in Washington, DC; Pan-STARRS; Juno; Tidal Disruption Events; Riess and Hubble constant tension

Greetings from Palmia Observatory

Well this has been the first full day of plenary sessions at the 231st meeting of the American Astronomical Society (AAS).  There has already been some really interesting presentations and I find I'm having a harder time to summarize what I heard, but here goes.  The AAS 231 was held outside of Washington DC, actually at National Harbor in Maryland.  There were way too many sessions to choose from, but my approach was to attend all of the plenary sessions and one special session dealing with Pan-STARRS telescope in Hawaii and how its publicly available data is being used and can be accessed by the public and citizen scientists and a short summary of those sessions will be presented.
Scott Bolton, SWRI, gave the Kavli Foundation Lecture at the first plenary session and he reviewed some of the scientific results coming in from the Juno orbiter around Jupiter.  He said that understanding the formation of Jupiter holds the keys to understanding the formation of the solar system.  Previous exploration of the clouds of Jupiter by Galileo probe in 1995 found higher levels of heavy elements, compared to that of the sun, but lower water than expected.  Juno was designed to resolve some of these issues of the formation of Jupiter and the Solar System.  It has a group of microwave radiometers to peer deep into the clouds and monitor how much water and ammonia and other gases are present as a function of altitude.  It has a magnetometer to study the magnetic field of Jupiter and a microwave transponder used to monitor the gravity field of Jupiter, which is already leading to improved understanding of the internal core of Jupiter.  He said that the clouds are quite variable in height and structure and it seems that Galileo just by chance had entered the atmosphere where the amount of water was just lower than normal.  More data will result in much better models.  He showed a lot of very interesting videos and simulations and models that I did not have time to capture the web references.  You can however find a lot of images and other details at:
https://www.missionjuno.swrl.edu


Ken Chambers and Eugene Magnier  provided an introduction of the two Pan-STARRS telescopes, located in Hawaii, which conducts wide whole sky surveys to find NEOs and supernovas.  The scopes are 1.8 meter aperture, f/4.4 with 3.2 degree field of view and a 1.5 gigapixel camera.  Pan-STARRS can achieve magnitude comparisons at the 8-10 milli-mag level and the 10-20 milli-arcsec location.  This large data base of observations is publicly available and might provide opportunities for citizen scientists to contribute.  The data archive page and more technical details is found at:
panstarrs.stsci.edu

Edward Schlafly, Hubble Fellow at LBNL, described a Pan-STARRS study of dust in the Milky Way and its survey of converting 2-dimensional dust maps into 3-dimensional dust maps.  It is not enough to be able to just say that so much dust is observed in any particular direction.  What is really needed is to how the 3-D structure of the dust, that is we might see a certain amount of dust in some direction, but what we really want to know is how is that dust distributed along that sight line.  More of the technical details and some great animated displays of how the amount of dust is arranged around our view of the Milky Way can be found at the website:
Argonaut.skymaps.info



Suzi Gezari, U of Maryland, discussed how Pan-STARRS was used to study Tidal Disruption Events (TDE).  Remember a TDE is when a star gets too close to a black hole and is pulled apart and pulled in to the black which results in a big flare of radiation.  The study combined data from GALEX and Pan-STARRS.  One of the first TDEs they studied was PS1-10ej, which is shown in the light curve graph below.  Theoretical models derived using these curves can provide estimates of the mass of the black hole.


Light Curve for TDE PS1-10jh (Source: Suvi Gezari AAS 231 presentation)
Light Curve for TDE PS1-10jh (Source: Suvi Gezari AAS 231 presentation)




Adam Riess, John Hopkins University,  made a presentation entitled, "A new measurement of the expansion rate of the universe", to a nearly standing room only ballroom.  Riess won the Nobel Prize for his earlier work identifying the acceleration of the universe by using supernovas as standard candles.  This presentation discussed some of the latest findings of the SHOES project, which has the goal of reducing the uncertainty in Hubble constant estimates from current 2.4% to 1% or lower.

A key part of the presentation was a comparison of the tension between two key projects that have made estimates of the Hubble constant.  First the Cosmic Microwave Background studies have fixed Hubble constant at 66.9 +/- 0.6 and the supernova study fixes it at 73.2 +/- 1.74.


Tension between Hubble constant = 66.9 per CMB and 73.2 for supernova study (Source: Adam Riess presentation)
Tension between Hubble constant = 66.9 per CMB and 73.2 for supernova study (Source: Adam Riess presentation)

Riess went over the various studies that contributed to both types of estimates and attributed the new HST scanning spatially scanning technique as a key improvement in gathering more and additional supernova light curve data.  He said the increased accuracy from Gaia and other sources is helping reduce the error in the distance measurement estimates.  He also said that the difference between these two estimates might come down to some effect and function of the red shift at which these measurements are made.  The supernova study uses single digit redshifts and the CMB data was set in place somewhere near redshift = 1300.

More data and reduced error estimates will help resolve which estimate is better.
Natalie Hinkel, VDA Fellow at Vanderbuilt U, presented a review of the stellar abundance database and the Hypathia Catalog.  She pointed out the importance of elements heavier than hydrogen.  Astronomers think of metals as anything heavier than Hydrogen/Helium, but other interdisciplinary scientists, like geologists and biologists, want to see more data on the heavy metals, like carbon, iron, sodium and potassium and other elements found so necessary for life.  The following table shows the current database for over 5000 stars and the abundances of heavy elements.





She also argued for extending the definition of the habitable zone for exoplanets to go beyond just a consideration of the temperature required for liquid water, to include typical heavy elements, now thought necessary for life as we know it.

Cayman Unterborn, Arizona State University, spoke as a geologist and how this concept of expanding the habitable zone to include the heavy elements for life also makes sense in terms of the possible geology of the exoplanet will have the right geochemistry to support the right exoplanet conditions, many of which are known on Earth to be necessary for life, such as plate tectonics and a magnetic field, might not be possible if the right combination of heavy elements are not found in the exoplanet.  So, if an exoplanet is at the right distance from its sun to maintain liquid water, if the chemical composition of the expoplanet does not have the right combination of heavy elements, then these geological processes, like plate tectonics and magnetic field, might not be present and this would result in the exoplanet really being more likely than not in the uninhabitable zone.

Nick Kaiser, winner of the RAS Medal Prize Lectureship, spoke on "The Effects of Non-linear Structure on Cosmological Observations."  This issue is one that I was wondering about too.  How is it that we know that the information we get about the structure of the universe, which we get primarily from light, has not itself been compromised by the structure of the universe interacting in a non-linear way.


Ok, that is about it for this first day of AAS.

Until next time,


If you are interested in things astronomical or in astrophysics and cosmology
Check out this blog at www.palmiaobservatory.com








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