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1. A Semi-Empirical Approach for Photometric Zeropoints Using Stars

   Seagraves, Maya; Beaton, Rachael; Durbin, Meredith; Desjardins, Tyler; Monson, Andrew (January 2024, 245th Meeting of the American Astronomical Society, id. 353.23. Bulletin of the American Astronomical Society, Vol. 57, No. 2 e-id 2025n2i353 p23)

   Understanding the detailed properties of stars in the infrared is of critical importance with new missions focusing on the infrared (JWST, Roman). The ground-based wide-field infrared instrument, FourStar, on the Magellan telescope contains a number of medium band filters that are optimized for photometric redshifts, but also provide nearly continuous spectral coverage for stars. These filters, however, lack absolute calibration. In this project, we adapted a technique used for galaxies to be used for stars. We used multi-band photometry to fit a likely SED model to each star and then generated synthetic photometry from the SED model to produce the magnitude of the star in a given filter. Statistically, we then determined the zero point in each filter in each image. This will be used to calibrate a large survey aiming to better understand near-infrared properties of stars for application to the extragalactic distance scale (with JWST and Roman). 

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2. A Semi-Empirical Approach for Photometric Zeropoints Using Stars

   Seagraves, Maya; Beaton, Rachael; Durbin, Meredith; Desjardins, Tyler; Monson, Andrew (January 2024, 245th Meeting of the American Astronomical Society, id. 353.23. Bulletin of the American Astronomical Society, Vol. 57, No. 2 e-id 2025n2i353 p23)

   Understanding the detailed properties of stars in the infrared is of critical importance with new missions focusing on the infrared (JWST, Roman). The ground-based wide-field infrared instrument, FourStar, on the Magellan telescope contains a number of medium band filters that are optimized for photometric redshifts, but also provide nearly continuous spectral coverage for stars. These filters, however, lack absolute calibration. In this project, we adapted a technique used for galaxies to be used for stars. We used multi-band photometry to fit a likely SED model to each star and then generated synthetic photometry from the SED model to produce the magnitude of the star in a given filter. Statistically, we then determined the zero point in each filter in each image. This will be used to calibrate a large survey aiming to better understand near-infrared properties of stars for application to the extragalactic distance scale (with JWST and Roman). 

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3. Beyond UVJ: Color Selection of Galaxies at z > 3

   Antwi-Danso, J. Papovich (January 2021, Bulletin of the American Astronomical Society)

   We calibrate and validate different methods of rest-frame color-color selection to identify galaxies in active star-forming and quiescent stages of their evolution. Our method is similar to the widely-used UVJ color-color diagram, which is an effective way to distinguish between quiescent and star-forming galaxies using their rest-frame U-V and V-J colors. UVJ colors suffer known systematics, and at z > 4 the method must be extrapolated because the rest-frame J-band moves beyond the coverage of the deepest bandpasses (typically IRAC 4.5 µm). This leads to biases: for example, spectroscopic campaigns have shown that UVJ-quiescent samples include ~10-30% contamination from galaxies with significant amounts of star formation. Alternative selection methods will be important not just to mitigate these biases, but also in the JWST era where NIRCam coverage is also limited to ~5 µm . In this poster, we present calibrations of alternative rest-frame filter combinations that are applicable for galaxies at redshifts z = 4 - 6. We apply our method to a stellar mass-limited sample of galaxies at 4 < z < 6 from the FLAMINGOS-2 Extragalactic Near-Infrared K-Split (FENIKS) survey. FENIKS is a deep (23.1 - 24.5 AB mag) survey employing two novel filters which split the Ks band ( λc = 2.2 µm) K-blue and K-red filters ( λc = 1.9 and 2.3 µm, respectively), allowing for finer sampling of the Balmer/4000 Å break of galaxies with evolved populations. We quantify the improvement in the selection of quiescent and star-forming galaxies using the alternative color-color selection methods. Furthermore, we investigate correlations between galaxy properties and their rest-frame colors, in particular examining purity and completeness of these selection methods. Finally, we explore the above for a wide range of synthetic filter combinations to inform accurate selections of various galaxy populations and rule out unphysical areas of parameter space for these populations. 

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4. The MOSDEF survey: an improved Voronoi binning technique on spatially resolved stellar populations at z ∼ 2

   https://doi.org/10.1093/mnras/staa2775  

   Fetherolf, Tara; Reddy, Naveen A; Shapley, Alice E; Kriek, Mariska; Siana, Brian; Coil, Alison L; Mobasher, Bahram; Freeman, William R; Sanders, Ryan L; Price, Sedona H; et al (September 2020, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT We use a sample of 350 star-forming galaxies at 1.25 < z < 2.66 from the Multi-Object Spectrograph For Infra-Red Exploration (MOSFIRE) Deep Evolution Field survey to demonstrate an improved Voronoi binning technique that we use to study the properties of resolved stellar populations in z ∼ 2 galaxies. Stellar population and dust maps are constructed from the high-resolution CANDELS/3D-HST multiband imaging. Rather than constructing the layout of resolved elements (i.e. Voronoi bins) from the signal-to-noise (S/N) distribution of the H160-band alone, we introduce a modified Voronoi binning method that additionally incorporates the S/N distribution of several resolved filters. The spectral energy distribution (SED)-derived resolved E(B − V)stars, stellar population ages, star-formation rates (SFRs), and stellar masses that are inferred from the Voronoi bins constructed from multiple filters are generally consistent with the properties inferred from the integrated photometry within the uncertainties, with the exception of the inferred E(B − V)stars from our z ∼ 1.5 sample due to their UV slopes being unconstrained by the resolved photometry. The results from our multifilter Voronoi binning technique are compared to those derived from a ‘traditional’ single-filter Voronoi binning approach. We find that single-filter binning produces inferred E(B − V)stars that are systematically redder by 0.02 mag, on average, but could differ by up to 0.20 mag and could be attributed to poorly constrained resolved photometry covering the UV slope. Overall, we advocate that our methodology produces more reliable SED-derived parameters due to the best-fitting resolved SEDs being better constrained at all resolved wavelengths – particularly those covering the UV slope. 

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5. First Observations of the Brown Dwarf HD 19467 B with JWST

   https://doi.org/10.3847/1538-4357/acb68b  

   Greenbaum, Alexandra_Z; Llop-Sayson, Jorge; Lew, Ben_WP; Bryden, Geoffrey; Roellig, Thomas_L; Ygouf, Marie; Fulton, B_J; Hey, Daniel_R; Huber, Daniel; Mukherjee, Sagnick; et al (March 2023, The Astrophysical Journal)

   Abstract We observed HD 19467 B with JWST’s NIRCam in six filters spanning 2.5–4.6μm with the long-wavelength bar coronagraph. The brown dwarf HD 19467 B was initially identified through a long-period trend in the radial velocity of the G3V star HD 19467. HD 19467 B was subsequently detected via coronagraphic imaging and spectroscopy, and characterized as a late-T type brown dwarf with an approximate temperature ∼1000 K. We observed HD 19467 B as a part of the NIRCam GTO science program, demonstrating the first use of the NIRCam Long Wavelength Bar coronagraphic mask. The object was detected in all six filters (contrast levels of 2 × 10⁻⁴to 2 × 10⁻⁵) at a separation of 1.″6 using angular differential imaging and synthetic reference differential imaging. Due to a guide star failure during the acquisition of a preselected reference star, no reference star data were available for post-processing. However, reference differential imaging was successfully applied using synthetic point-spread functions developed from contemporaneous maps of the telescope’s optical configuration. Additional radial velocity data (from Keck/HIRES) are used to constrain the orbit of HD 19467 B. Photometric data from TESS are used to constrain the properties of the host star, particularly its age. NIRCam photometry, spectra, and photometry from the literature, and improved stellar parameters are used in conjunction with recent spectral and evolutionary substellar models to derive the physical properties of HD 19467 B. Using an age of 9.4 ± 0.9 Gyr inferred from spectroscopy, Gaia astrometry, and TESS asteroseismology, we obtain a model-derived mass of 62 ± 1M_J, which is consistent within 2σwith the dynamically derived mass of ${81}_{-12}^{+14}$M_J. 

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