Thursday, November 19, 2015

Welcome to the Circumstellar & Interstellar Matter Blog

Circumstellar & Interstellar Matter (CIM) Journal Club is a biweekly meeting at The Space Telescope Science Institute. Attendees to the meeting include senior astronomers, postdocs, and graduate students with an interest in CIM. We host both local and external speakers who present their recent work, review a recently-attended conference, or discuss a recently-read paper. Topics include the ISM, dust, star formation, and evolved stars.

When: CIM Journal Club meets biweekly for an hour, usually on Fridays from 13:00 - 14:00.
Where: CafeCon
Contact: CIM Journal Club is organized by Jonathan Seale at STScI (seale @ stsci.edu).

Friday, November 16, 2012

November 16, 2012 Meeting

Speaker: Nick Indriolo (JHU)

Title: Direct Determination of the HF/H2 Abundance Ratio in Interstellar Gas


Abstract: We report the first detection of the v=1-0, R(0) ro-vibrational transition of HF at 2.49938 microns arising from interstellar gas. The line is seen in absorption toward 3 background sources---HD 154368, Elias 29, and AFGL 2136 IRS 1---all of which have reported H_2 column densities determined from observations of H_2. This allows for the first direct determination of the HF/H_2 abundance ratio. We find values of N(HF)/N(H_2)=1.15*10^-8 and 0.69*10^-8 for HD 154368 and Elias 29, respectively. The sight line toward AFGL 2136 IRS 1 also shows absorption from the v=1-0, R(1) transition of HF, indicating warm, dense (n_H>10^9 cm^-3) gas, likely very close to the central protostar. Ascribing portions of the HF absorption to warm and cold gas, we find N(HF)/N(H_2)=(1.7--2.9)*10^-8 and (2.4--4.3)*10^-9 for the two components, respectively. Except for the warm component toward AFGL 2136 IRS 1, all observed HF/H_2 ratios are well below N(HF)/N(H_2)=3.6*10^-8, the value predicted if nearly all gas-phase fluorine is in the form of HF. Models of fluorine chemistry that account for depletion onto grains are able to reproduce the results toward HD 154368, but not in the cold, dense gas toward AFGL 2136 IRS 1 and Elias 29. Most likely, some combination of simplifying assumptions made in the chemical models are responsible for these discrepancies.

Wednesday, November 7, 2012

November 9, 2012 Meeting

Speaker: Nicholas Flagey (CalTech, JPL)

Title: Investigation of MIPSGAL 24 ┬Ám Compact Bubbles: Hunting for the Missing Massive Stars in the Galaxy

Abstract: Click here!

Wednesday, October 17, 2012

October 19, 2012 Meeting

Speaker: Iain McDonald (University of Manchester)

Title: Stellar Death at Low Metallicity

Abstract: From the dust in the earliest galaxies to the elements making up rocky planets today, all astronomical metals have been made in successive generations of stars and returned to the interstellar medium (ISM) through these stars' subsequent demise. To understand the transition from pristine gas to the complex mixture of the ISM today, we must understand the life and - particularly - the death of the low-metallicity stars that have come before us. In this seminar, I will talk about death: that of (low-mass) metal-poor stars and how it differs from the solar-metallicity stars we see around us. I will discuss how the chemical and mineralogical return from these stars to space has changed over time, and the differences this implies for studying the  high-redshift Universe.

Tuesday, October 9, 2012

October 15, 2012 Meeting

Speaker: Benne Holwerda, ESA

Title: Quantifying HI Morphology

Abstract: The classification of the morphology of galaxies at any wavelength has for a long time been the realm of the human eye. While powerful, this made the classification inherently subjective. One approach to quantify and objectify morphological classification is to use several scale-invariant parameters to span the space of galaxy types: concentration, asymmetry, smoothness, Gini distribution index, and the second order moment of brightest regions (M20).

These parameters have proven themselves useful in identifying ongoing major merger events in the near and distant Universe by quantifying the morphology of galaxies in star-formation dominated wavelengths (ultraviolet and blue optical). I applied these parameters for the first time to samples of atomic hydrogen (HI) column density maps, reasoning that before the triggered star-formation, the HI disks of late-type galaxies is severely affected by the merger or tidal event. The motivation was to find a more sensitive, reliable and possibly longer lasting morphological identification of merger events, initially in the nearby Universe but with SKA possibly applicable further afield.

I will present results from several HI surveys, identifying the fraction of mergers through their HI morphology, the visibility time scale from simulations and an first estimate of the volume merger rate based on the WHISP survey for the local Universe. In addition, I identified Extended UltraViolet Disks (XUV) through their ultra-violet and HI maps and discuss what can be said about their origin. Two surveys are poised to map the entire sky in HI at high resolution and sensitivity, the WNSHS survey with WSRT/APERTIF  in the Netherlands and the WALLABY survey with the ASKAP telescope in Australia. Quantified morphology of the thousands of observed galaxies will provide the statistics to identify ongoing mergers, unique systems, stripped HI disks etc.

Friday, September 21, 2012

October 5, 2012 Meeting

Speaker: Andrew Fox, STScI

Title: Chemical and Physical Conditions in the Magellanic Stream

Abstract: The inflow of gas onto galaxies is a key driver of their formation and evolution. A prime local example of a gas flow is the Magellanic Stream (MS), a massive tail of material stripped out of the Magellanic Clouds and extending for almost 200 degrees across the Southern sky. The MS appears to be fragmenting and evaporating as it interacts with the hot Galactic corona, and it remains unclear how much of its neutral gas will survive to reach the Galactic disk to fuel future star formation. I will present recent results from an ongoing observing campaign on the MS, using UV (HST/COS) and optical (VLT/UVES) spectroscopy, paying particular attention to the chemical and physical conditions in the gas.

Thursday, September 13, 2012

September 21, 2012 Meeting

Speaker: Margaret Meixner, STScI
PDF of Presentation
Title: A Review of the Recent Magellanic Clouds Workshop in Perth, Australia

Abstract: The close promixity of the Magellanic Clouds to the Milky Way provides us with a unique laboratory to study various astrophysical processes such as star formation in low metallicity environments, feedback processes in the interstellar medium, and physical roles of galaxy interaction in chemical and dynamical evolution of gas-rich galaxies. These processes are fundamental to our understanding of galaxy formation and evolution in the Universe. Recent high-resolution observational data in different wavelength regimes have revealed much new data regarding stellar populations, clusters, the multi-wavelength properties of star-forming regions, and the dynamics of the Magellanic System. These data open the door to further studies of the formation and evolution of the System, and galaxies in general. Good examples are the new proper motions measurements of the Clouds, and the various models that have been generated to trace their past and future orbital and interaction history. It has been some time since the last major international conference related to the Magellanic System was held. Therefore, next year is a timely opportunity to re-assess this exciting field. The principle aim of this meeting is to compare the latest observational results with the corresponding recent theoretical models.