Sketching the 240th Meeting of the American Astronomical Society
Olivia Wilkins
I’m sitting outside the Hilton at the Chicago O’Hare, waiting for the bus that will whisk me away to Urbana, Illinois for the International Symposium on Molecular Spectroscopy, or ISMS. I was just at O’Hare yesterday, where I changed planes on my way back to Maryland from another conference in southern California. I sure am looking forward to having a few days off from flying!
Last week, I attended the 240th Meeting of the American Astronomical Society (AAS, which I say, “Double-A-S”) in Pasadena, California. The conference, which started on June 12, came at a perfect time because it began just two days after my graduation where I celebrated completing my Ph.D., also in Pasadena. National conferences like the AAS meeting jump from place to place each year, so it was pure luck that I could attend the most recent one back-to-back with my graduation from Caltech.
When I attend science conferences, I often sketch summaries about the talks and share them on Twitter using the hashtag #SciConSketch. Sketching talk summaries instead of taking extensive notes helps me focus on the key points. It also provides me with a picture that helps me visualize the notes and find them more easily later. Most of the time, talks at conferences are based on recently or soon-to-be published papers, so knowing the name of the presenter and the general idea of their presentation is sufficient if I want to find more details later.
During most of the AAS conference, I attended presentations at the joint Laboratory Astrophysics Division (LAD) meeting. I sketched those talks I attended… even when I was chairing one of the sessions! The illustrated summaries are below, along with the text typed out to make it more accessible.
I hope you enjoy!
Monday, June 13, 2022
The Salty Solar System - I
Platinum Group Elements in Neutron Star Mergers — Steven Bromley (Auburn University)
In the top left is a sketch of a neutron star merger. To the right of that are the element symbols for rhenium, osmium, iridium, and platinum with the text “Over time: T[emperature] and ionization go up.” At the bottom, there are two diodes representing those used in the experiments discussed to study atomic chemistry in neutron star mergers simulated in the lab. The text reads, “Nickel and gold probes facing W[the chemical symbol for tungsten]-powered plasmas inside a fusion device to study Au [gold]; Pt[platinum]-group elements are actively being studied.”
Frozen Brines: Experimental Insights into Europa’s Surface Chemistry — Paul Johnson (NASA JPL)
On the left is a sketch of Europa. “Europa is ‘smooth’ so [its] surface is being refrozen and refreshed.” In the experiments discussed, four-component brines composed of sodium (Na), magnesium (Mg), sulfate (SO4), and chloride (Cl) were studied. The right column shows some of the specific reactions observed. In the study, it was found that slow freezing led to crystalline ice structures, whereas flash freezing led to glassy ices. Further experiments showed that glassy ices on Europa “could have micro-organisms!” because some microbes survived the flash freezing process in the lab.
Probing Space Weathering of Lunar Regolith with Nanoscale Imaging and Spectroscopy — Adam Grice (University of Georgia)
In these studies, a cantilever (brown probe in the top left sketch) scanned a sample of lunar regolith, which is just a fancy way of saying moon dust. A laser was reflected off the top of the probe and directed into a detector, which was used to measure spectra of the sample (plot in the bottom left). The “spectra reveal [the] composition. If [the spectra of moon dust can be] recreated in terrestrial sample, good to go; if not, [that is a] sign of space weathering.”
RAS Gold Metal Lecturer: Women in Astrophysics Plenary
Women in Astrophysics - In Time and Place — Jocelyn Bell Burnell (Oxford)
In 1990, “women in astronomy [was seen as] a “social issue” [and] not something the IAU [International Astronomical Union] would take on.” The plot shows a sketch of women membership in the IAU between 2005 and 2020, over which it increased from about 12% to 18%. The map shows (roughly) countries where IAU woman membership is above average (green, +) and below average (orange, -). Interestingly, “English speaking countries have tended to be below average” consistently.
At 2:00 p.m., I gave my dissertation talk, “High Resolution Imaging of the Orion Kleinmann-Low Nebula,” in the Molecular Cloud Chemistry session. I don’t have a sketch for that, but wanted to mention it anyway :)
The Salty Solar System - II
Laboratory Studies of Ammonium Salts — Perry Gerakines (NASA GSFC)
“67P [the comet in the top left of the sketch] is extremely salty.” The dust and ice enveloping the comet have been found to contain ammonium chloride (NH4Cl), ammonium cyanide (NH4CN), and ammonium cyanate (NH4OCN), among others. To measure how much salt is in the comet, a measure called the "column density" is used (which is mass over area, since we don't know how deep the material measured is). The column density N is the ratio of the intensity of the emission at a given wavelength, which comes from telescopes, over the band strength A. This is also expressed as N = nh, where n is the number density (or molecules per unit volume) and h is the thickness of the ice. The band strength is surrounded by question marks because this is the unknown for astronomers. Thus, the band strength is what is measured in the lab. In the bottom left is a sketch of the experimental set-up in which an ice is deposited on a gold substrate. A laser is used to measure the ice thickness h at many different ice thicknesses. Since the number density times ice thickness is inversely proportional to the band strength, this technique can be used to determine the band strength for different ices, which can in turn be used to estimate how much of an ice is in a comet. The bottom line gives an example of the work discussed and shows the reaction HCN + NH3 → NH4CN.
Rotational Spectroscopy as a Sublime Tool for Identifying Organic Products of UV-Photolyzed Cosmic Ice Analogues — Olivia Wilkins (NASA GSFC)
My second talk of the day, only an hour after my first. I don’t have a sketch for this one either.
Ortho/Para Ratio of Formaldehyde Formed in UV-Photolyzed Interstellar Ice Analogs — Katarina Yocum (NASA GSFC), AKA my lab mate!
Some molecules have different flavors called spin isomers in which the hydrogen atoms on the molecules either spin in a parallel or anti-parallel manner. When the spins are parallel, the molecule is said to be “ortho” (and has odd Ka quantum numbers); when they are anti-parallel, the molecule is said to be “para” (and has even Ka quantum numbers). In this work, formaldehyde (H2CO) was discussed, specifically in the context of probing the conditions for organic formation in the interstellar medium. The right column shows two scenarios: a cold, solid-state formation on icy dust grains, which is theorized to give an ortho/para ratio of less than 3, and a warm gas-phase formation, which is theorized to yield an ortho/para ratio of exactly 3. However, some studies of water, which was expected to exhibit similar behavior, “[show] o[rtho]/p[ara] ratio of 3 regardless of formation T[emperature]; is H2CO the same?” This is a question Katarina and I are hoping to answer in the lab.
Tuesday, June 14, 2022
Spectroscopy
The Molecular Outlook in Astrophysics: Past, Present, and Future — Evelyne Roueff (l’Observatoire Paris), 2022 Laboratory Astrophysics Prize
Astrochemistry arguably goes back to 1937, when “CH was [the] first molecule detected in space” (top left). Even though molecular hydrogen (H2) is the most abundant molecule in space, it is a difficult molecule to detect. In 1970, “H2 [was] finally detected… by rocket!” (top middle) when a spectrometer aboard a rocket detected signatures of the molecule. Since then, “much has been done to characterize the H2 electronic spectrum.” On the middle left, the sketch gives the characteristics of diffuse clouds: column density nH ~ 102-103 cm-3 and gas temperature Tgas ~ 70 K[elvin]. The sketch of the grain shows one of the mechanisms for molecular hydrogen. H2 forms on grains: Since 1970, much has been done to observe H2 in different environments. Challenges for the Future: determining line intensities; non-linear effects in models.
H2O Collides with H2, Vibrational Quenching — Laurent Wiessenfeld (l'Observatoire Paris)
A lot of astrochemical models of gas-phase collisions between molecular hydrogen (H2) and water (H2O) consider molecular rotations only. However, in reality, the water molecule will be subject to both rotation and vibration, which is a more complicated collisional calculation. As written above the sketch of the James Webb Space Telescope (JWST) on the right, "Rovibrational information is need[ed] for observations of hotter material, e.g., with JWST."
History of Spectroscopic Instrumentation - II
An Unexpected Story: The Making of Early Astrophysics — Robert W. Smith (University of Alberta)
This talk described three ages of early astrophysics. First, between about 1860 and 1890, astronomers were mostly amateurs who charted spectral lines and star positions. It wasn’t until the second era, between 1890 and 1920, that there was a “growing number of practitioners.” Like the earlier astronomers, these folks were not professionals in the modern sense, but they did collect data, albeit not rigorously. Instead, much of the data collection of this age centered on cataloguing stars. Finally, the era between 1920 and 1950 saw a shift toward problem-solving-based questions. At this point, mere observation began to shift to answering scientific questions about the universe.
Radio Astronomy and Spectroscopy: Bell Labs to ALMA — Tony Remijan (NRAO)
In 2021, about 40 molecules were detected in the ISM [(or interstellar medium)] for the first time. In general, these molecules are much more complex than the groundbreaking molecular detections of decades past. In 1969, the detection of formaldehyde (H2CO) in Sagittarius A (Sgr A) showed that not only were there molecules in space (the methylidine radical, CH, had been detected in 1937), but they could be polyatomic (i.e., have many atoms). The following year, in 1970, carbon monoxide (CO) was mapped across the entire galaxy, showing that molecules are ubiquitous across the Milky Way. Radio telescopes have been used to search for even more complex molecules, such as glycine—widely considered the "holy grail" of astrochemistry. Glycine has not been detected, however "searches led to serendipitous detections of other complex species." As stated to the left of the sketch of ALMA (right side), "with interferometry (e.g., ALMA) we can map origins of molecules in hot cores." The bottom left shows the Green Bank Telescope (GBT), because "for really big molecules, centimeter (cm) wavelengths (e.g., with the GBT) are needed."
Galactic Chemical Abundance Studies — Chris Sneden (UT Austin)
“Nearly a century ago, metal-poor stars [were] first discovered using Mount Wilson Observatory,” which is sketched in the top left. “Since then, 43 elements with [proton number] Z>30 (i.e., metals beyond iron) have been found… but with lots of hesitation.” There are several instances of someone detecting a new metal but having doubts, even with strong spectroscopic evidence. The talk concluded by talking about how we “need laboratory astrophysics measurements to characterize data from cool stars.” An example of a set-up with a green laser is shown in the bottom right.
Laboratory Astrophysics Division Plenary
Comets as Natural Laboratories — Dennis Bodewits (Auburn University)
Interestingly, what constitutes a comet isn’t well constrained. In fact, “comets and asteroids are on a continuum.” What we do know is that comets have a nucleus of dust and ice, and as they approach the Sun, they form an outgassing tail and become surrounded by dust. There are several avenues by which chemical processes take place in the comae surrounding comets; these are shown in the middle. From top to bottom, these include fluorescence emission, gas collisions, photodissociation, electron impact dissociation, and charge transfer.
Wednesday, June 15, 2022
A Universe of Carbon - I
An Observational Perspective on Large Carbonaceous Molecules — Els Peeters (Western Institute for Earth & Space Exploration)
In the infrared (IR, represented by the red shading), galaxies exhibit emission from large carbon molecules. These signatures are aromatic infrared bands and span 3 to 10 microns (approximately). These signatures are thought to be from polycyclic aromatic hydrocarbons (PAHs), several of which were first detected in the radio in 2021. These bands depend on environment. JWST (bottom left) is expected to be ground-breaking in this area.
Using ALMA to Constrain the Structure of Epsilon Eridani Debris Disk — Brandon Hilliard (CU Boulder ** Not part of the LAD session; I popped into another session to cheer on a friend who is in their first year of grad school **
Epsilon eridani (left) is a face-on system with evidence of a debris disk, similar to the Kuiper belt. ALMA (right) gave us the highest resolution image of the disk so far. This system is worth studying because the structure of a disk is related to planet formation.
Spatially Resolved PAH Emission in the Protoplanetary Disk HD 97048 — Charles Mentzer (University of Missouri)
In HD 97048, polycyclic aromatic hydrocarbon (PAH) features vary across the disk, namely in the northeast versus the southwest, as observed with the Very Large Telescope (VLT). This is seen at radii of 14 au, where the column densities are about the same. At further out radii, there is (possible) evidence of PAH destruction from high-energy photons.
A Universe of Carbon - II
This was the first session I ever chaired! Sketching talks while keeping track of time and facilitating questions was a new challenge.
Photophysics of C60, Graphene and Carbon Nanotubes in Space — Aigen Li (University of Missouri)
Carbon (C) is the fourth most abundant element in the universe. In the ISM, 60% of carbon atoms are in dust, 40% are in gas. Models require UV/optical absorption, stellar spectra, and other parameters like vibrational profile. Dust is made of graphite, diamond, polycyclic aromatic hydrocarbons (PAHs), C60 (buckminsterfullerene, or buckyballs), C70, and other allotropes. At 2175 Angstroms, a spectral feature has been observed, begging the question, "Is there a buckyion signature?" Some examples of carbon structures that have been detected from spectra include graphene; "e.g., C24 may have been detected." Graphene comprises "up to 6% of all carbon." Carbon nanotubes (specifically, single-walled) are another carbon allotrope. In the lab, such nanotubes have diameters of 2.0 nanometers. These structures comprise "up to 4% of all C[arbon]."
Rotational Spectroscopy of Astrophysically-Relevant Molecules — Marie-Aline Martin-Drumel (University of Paris)
About 270 molecules have been detected in space. Of these, 90% have been detected via radio astronomy. "Rotationally resolved spectra, [like the illustration on the top right, which are observed with radio telescopes,] enable unambiguous detections of molecules, including isomers, conformers, and isotopologues. Spectra are like barcodes on cheese" (which Marie-Aline said she used as an analogy since she is French) in that every molecule has a unique rotational spectrum, just like every type of cheese in a shop has a unique barcode. Observing molecules in space requires that their spectra be characterized in the lab, and "to measure [a] variety of compounds in the lab, experiments must be versatile." For example, deuterated ammonia—NHD and ND2—were "detected in space because of far-IR [far-infrared] characterization" in the lab.
Transition Electron Microscopy of SiC Grains — Jacob Bernal (University of Arizona)
This talk addressed the question, “How are space fullerenes synthesized?” It looked at silicon carbide, or SiC, because “SiC is abundant, but emission is not seen in [the interstellar medium] ISM.” That is, the research discussed looked at SiC as a possible avenue to space fullerenes. In the experiment, an SiC sample was heated to about 1300 Kelvin, which is a temperature similar to that in post-AGB shocks. Experiments were also conducted under ultrahigh vacuum (UHV). On the right, it can be seen that a graphene surface formed on the SiC. Zooming in, you can see carbon “nano buds” that eventually grow into multi-walled carbon nanotubes.
Laboratory Studies of Cosmic Dust Analogs: Carbon in the Universe — Farid Salama (NASA Ames)
The discussed work involves a vacuum chamber (left) where a sonic expansion takes place. The chemistry inside is observed using a method called cavity ring-down spectroscopy. In the experiment, hydrocarbon gas (e.g., methane, or CH4, and acetylene (C2H2) are converted into dust analogues.
A Universe of Carbon - III
Rotational Spectroscopy of Nitrogen-Containing Radicals — Kyle Crabtree (UC Davis)
As long as a molecule has a dipole moment, it can be measured with rotational spectroscopy. The Crabtree lab uses rotational spectroscopy to study nitrogen-containing compounds. Why nitrogen? Nitrogen heterocycles, which are relevant to life, are found in meteorites. Specifically, nitrogen radicals are studied in the lab. Radicals produce a forest of lines. Some of the radicals studied have included the three pyridyl radicals, each of which have slightly different rotational spectra (see bottom left).
Investigating Titan’s Atmospheric Chemistry with ALMA — Alexander Thelen (NASA GSFC)
Titan, one of the moons of Saturn, has a hazy atmosphere that is 94-98% nitrogen (N2), 1-5% methane (CH4), and 0.1$ molecular hydrogen (H2). ALMA observations revealed seasonal HC3N emission, and more, including four new species newly detected in Titan.