Special Talk

• Special Talks

  Speaker: Jimena Rodriguez (STScI)
  Title: From Massive Young Stellar Objects to Stellar Clusters: Resolving the Earliest Stages of Star Formation with JWST
  Abstract: The formation of stars and stellar clusters is inherently multiscale, spanning from individual protostars to star-forming complexes tens of parsecs across. While the earliest stages of star formation can be studied in detail within the Milky Way and Magellanic Clouds, connecting these local insights to the broader population of young stellar systems in nearby galaxies remains a major challenge. In this talk, I will present a JWST study of massive young stellar object (MYSO) candidates in four nearby galaxies at distances of 1–5 Mpc using NIRCam and MIRI imaging. We define mid-infrared color selection criteria to identify embedded young sources and quantify how spatial resolution affects both source selection and physical interpretation. We find that the color selection remains largely stable with distance, but blending and surface-brightness effects increasingly bias source characterization in more distant systems. Spatial resolution also affects the origin of the observed mid-infrared emission: clustering enhances the fraction of emission attributed to compact sources in active star-forming regions, while blending into diffuse emission dominates in more quiescent environments. These effects introduce systematic biases in samples of embedded young objects and establish a practical limit of approximately 3 Mpc for studying individual MYSOs with JWST. This work provides a foundation for future resolved studies of star formation and early cluster evolution, while offering guidance for interpreting embedded stellar populations across a broad range of galactic environments.

  Speaker: Rodrigo Angulo (JHU)
  Title: Astronomical Time Machine: Light Echoes Reveal Eta Car’s Great Eruption
  Abstract: The Great Eruption (GE) of Eta Carinae (Eta Car) in the mid-1800s was a spectacular astronomical event, visible to the naked eye (Smith+Frew 2011). It arose from a greater than 100-solar-mass evolved star in an eccentric binary system that suddenly ejected about 20 solar masses of material, today seen as the bipolar Homunculus nebula. The discovery of light echoes of Eta Car's GE (Rest+2012) now offers us the opportunity to re-observe the entire event with modern instrumentation, a true astronomical time machine! With more than 10 years of monitoring the light echoes, we are now able to reconstruct the full 20+ year GE light curve to very high accuracy in griz, and connect it to spectroscopic observations! While we can confirm the 3 peaks of the GE in the historic light curve, we find that the GE dramatically reddens during the 3rd peak, and also we find a 4th peak. In addition, we are able to probe the photometric asymmetry of the same event, and we find that in one direction, the light curve derived from the light echoes is strikingly different from the other directions as well as from the historic light curve. With this new information, we are now able to further constrain the physical mechanism behind the GE, the proto-type of eruptive mass loss, luminous blue variables, and supernova impostors.

  Speaker: Benjamin Gibson (STScI)
  Title: Bizarre BADGRs: Unravelling the Mysterious ISM of Blue And Dusty Gas Rich Sources
  Abstract: There exists in the universe a previously-overlooked class of galaxies with bizarre ISM properties: BADGRs. These galaxies are very blue and flocculent, they contain more HI by mass than stars, and are the most dust-rich galaxies within ~10 Mpc. However, despite their dust, BADGRs absorb 5-20 times less UV radiation than a typical late-type galaxy. Even more confoundingly, these galaxies are actively star-forming despite being low in molecular gas, and have unusually cold dust for the intensity of their UV radiation.

  To unravel these mysteries, we have extracted panchromatic photometry from archival imagery of two nearby BADGRs: NGC7793 and NGC4449. With the sensitivity of JWST, we resolved millions of individual stars in each galaxy, and with HST's exquisite wavelength coverage, have data in as many as nine filters from the UV to the IR. Using the Bayesian Extinction And Stellar Tool (BEAST), we have performed SED fitting to nearly 1.5 million stars in these galaxies, providing precise measurements of, most notably, the stars' masses, ages, luminosities, and temperatures, as well as characterized the dust extinction along the line of sight. These measurements enable the construction of high-resolution extinction maps for both galaxies, and provide new insight into the ISM geometry and star formation physics that drive the unusual properties of BADGRs.