[
{
"id": "authors:6wzzx-9p192",
"collection": "authors",
"collection_id": "6wzzx-9p192",
"cite_using_url": "https://authors.library.caltech.edu/records/6wzzx-9p192",
"type": "article",
"title": "Spectral Response of SPHEREx",
"author": [
{
"family_name": "Hui",
"given_name": "Howard",
"orcid": "0000-0001-5812-1903",
"clpid": "Hui-Howard"
},
{
"family_name": "Bock",
"given_name": "James J.",
"orcid": "0000-0002-5710-5212",
"clpid": "Bock-J-J"
},
{
"family_name": "Condon",
"given_name": "Samuel",
"orcid": "0000-0003-4255-3650"
},
{
"family_name": "Dowell",
"given_name": "C. Darren",
"orcid": "0009-0002-0098-6183",
"clpid": "Dowell-C-Darren"
},
{
"family_name": "Jeong",
"given_name": "Woong-Seob",
"orcid": "0000-0002-2770-808X"
},
{
"family_name": "Jo",
"given_name": "Young-soo",
"orcid": "0000-0003-3574-1784"
},
{
"family_name": "Korngut",
"given_name": "Phil M.",
"orcid": "0009-0003-8869-3365",
"clpid": "Korngut-Philip-M"
},
{
"family_name": "Manatt",
"given_name": "Kenneth",
"orcid": "0009-0009-5777-4457",
"clpid": "Manatt-Kenneth"
},
{
"family_name": "Nguyen",
"given_name": "Chi",
"orcid": "0000-0001-9368-3186",
"clpid": "Nguyen-Chi"
},
{
"family_name": "Nguyen",
"given_name": "Hien",
"clpid": "Nguyen-Hien"
},
{
"family_name": "Padin",
"given_name": "Stephen",
"orcid": "0009-0001-9993-4393",
"clpid": "Padin-Stephen"
},
{
"family_name": "Park",
"given_name": "Sung-Joon",
"orcid": "0009-0001-4064-9918"
},
{
"family_name": "Pyo",
"given_name": "Jeonghyun",
"orcid": "0000-0001-9937-8270"
},
{
"family_name": "Yang",
"given_name": "Yujin",
"orcid": "0000-0003-3078-2763"
},
{
"family_name": "Ashby",
"given_name": "Matthew L. N.",
"orcid": "0000-0002-3993-0745"
},
{
"family_name": "Bach",
"given_name": "Yoonsoo P.",
"orcid": "0000-0002-2618-1124"
},
{
"family_name": "Chang",
"given_name": "Tzu-Ching",
"orcid": "0000-0001-5929-4187",
"clpid": "Chang-Tzu-Ching"
},
{
"family_name": "Cheng",
"given_name": "Yun-Ting",
"orcid": "0000-0002-5437-0504",
"clpid": "Cheng-Yun-Ting"
},
{
"family_name": "Chiang",
"given_name": "Yi-Kuan",
"orcid": "0000-0001-6320-261X"
},
{
"family_name": "Cooray",
"given_name": "Asantha",
"orcid": "0000-0002-3892-0190",
"clpid": "Cooray-A"
},
{
"family_name": "Crill",
"given_name": "Brendan P.",
"orcid": "0000-0002-4650-8518",
"clpid": "Crill-Brendan-P"
},
{
"family_name": "Cukierman",
"given_name": "Ari J.",
"orcid": "0000-0002-7471-719X",
"clpid": "Cukierman-Ari-J"
},
{
"family_name": "Dor\u00e9",
"given_name": "Olivier",
"orcid": "0000-0001-7432-2932",
"clpid": "Dor\u00e9-O"
},
{
"family_name": "Faisst",
"given_name": "Andreas L.",
"orcid": "0000-0002-9382-9832",
"clpid": "Faisst-Andreas-L"
},
{
"family_name": "Hora",
"given_name": "Joseph L.",
"orcid": "0000-0002-5599-4650"
},
{
"family_name": "Kang",
"given_name": "Jae Hwan",
"orcid": "0000-0002-3470-2954",
"clpid": "Kang-Jae-Hwan"
},
{
"family_name": "Lee",
"given_name": "BoMee",
"orcid": "0000-0003-1954-5046",
"clpid": "Lee-BoMee"
},
{
"family_name": "Lisse",
"given_name": "Carey M.",
"orcid": "0000-0002-9548-1526"
},
{
"family_name": "Masters",
"given_name": "Daniel C.",
"orcid": "0000-0001-5382-6138",
"clpid": "Masters-Dan"
},
{
"family_name": "Paladini",
"given_name": "Roberta",
"orcid": "0000-0002-5158-243X",
"clpid": "Paladini-Roberta"
},
{
"family_name": "Rustamkulov",
"given_name": "Zafar",
"orcid": "0000-0003-4408-0463",
"clpid": "Rustamkulov-Zafar"
},
{
"family_name": "Tolls",
"given_name": "Volker",
"orcid": "0000-0003-1841-2241"
},
{
"family_name": "Werner",
"given_name": "Michael W.",
"orcid": "0000-0003-4990-189X",
"clpid": "Werner-Michael-W"
},
{
"family_name": "Zemcov",
"given_name": "Michael",
"orcid": "0000-0001-8253-1451",
"clpid": "Zemcov-Michael"
}
],
"abstract": "\n
The Spectro Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx) is conducting the first all-sky near-infrared spectral survey spanning 0.75–5.0 μm with resolving power R ≈ 35–130. Linear variable filters mounted in front of six H2RG detectors produce a position-dependent spectral response across the focal plane. This paper presents the ground-based spectral calibration of SPHEREx, including the cryogenic apparatus, optical configuration, measurement strategy, analysis pipeline, and resulting calibration products. Monochromatic wavelength scans are used to derive the spectral response function, band center, and resolving power for every pixel. Band centers are measured to better than 1 nm for Bands 1 through 4 (0.75–3.82 μm) and better than 10 nm for Bands 5 and 6 (3.82–5.0 μm). Out-of-band leakage is negligible for detectors above 1.64 μm and is present at the percent level below this wavelength. The resolving power is measured to within 5% and agrees with design expectations to within 10%. An on-sky spectrum of the Cat’s Eye Nebula (NGC 6543) constructed from repeated observations provides in-flight verification and shows agreement between ground-calibrated response and astrophysical emission features. Calibration products, including per-pixel band center and resolving power maps, are released through IPAC to support community use of SPHEREx data. The absolute spectral calibration will continue to improve through in-flight measurements, with further reductions in uncertainty expected for the longest-wavelength bands.
\n
\n
We present some of the first infrared spectral maps acquired by SPHEREx. These maps, which to our knowledge are the largest of their type ever compiled in the near-infrared, reveal multiple strong lines due to interstellar ices and polycyclic aromatic hydrocarbons (PAHs) throughout the Cygnus X and North American Nebula regions. The maps emphasize the strongest features arising from the 3 μm H2O, 4.27 μm CO2, and 4.67 μm CO lines and the 3.28 μm PAH feature, all of which are detected over large areas with complex and filamentary spatial distributions. The ice absorption maps of H2O and CO2 in particular broadly trace dense, cold, and well-shielded regions across Cygnus X, consistent with the established picture of efficient ice formation in dense molecular clouds. The interstellar ice features are also detected abundantly in diffuse absorption over wide areas. The relative strengths of the H2O and CO2 features vary among different lines of sight, indicating possible differences in local physical conditions or chemical variations. The 3.28 μm PAH emission correlates with the emission from the 7.7 and 11.2 μm features but shows small differences that may trace the grain-size distribution and variations in the ambient UV field. SPHEREx all-sky spectral imaging—only a small fraction of which is showcased in this work—will support numerous science investigations, including the structure of the Galaxy, the physics of the interstellar medium, and the chemistry of stars.
\n
\n
From 2025 August 1 to August 15 UT, the SPHEREx spacecraft observed interstellar object 3I/ATLAS. Using R = 40–130 spectrophotometry at λ = 0.7–5 μm, lightcurves, spectra, and imaging of 3I were obtained. From these, robust detections of water gas emission at 2.7–2.8 μm and CO2 gas at 4.23–4.27 μm plus tentative detections of 13CO2 and CO gas were found. A slightly extended H2O coma was detected, and a huge CO2 atmosphere extending out to at least 4.2 × 105 km was discovered. Gas production rates and 1σ errors for H2O, 12CO2, 13CO2, and CO were Qgas = 3.2 × 1026 ± 20%, 1.6 × 1027 ± 10%, 1.3 × 1025 ± 25%, and 1.0 × 1026 ± 25%, respectively. Coaddition of all λ = 1.0–1.5 μm scattered light continuum images from 3I produced an image with high signal-to-noise ratio consistent with an unresolved source. The lightcurve of scattered light showed \u227215% variability over the observation period. The absolute brightness of 3I at 1.0–1.5 μm is consistent with a nucleus of <2.5 km radius surrounded by a 100 times brighter coma. The 1.5–4.0 μm continuum structure shows a strong spectral feature commensurate with water ice absorption seen in Kuiper Belt objects and distant comets. The observed cometary behavior of 3I, including its preponderance of CO2 emission, lack of CO output, small size, and predominance of large icy chunks of material in a flux-dominant coma, is similar to the behavior of short-period comet 103P/Hartley 2, the ”hyperactive, strongly thermally processed comet” flyby target of the NASA Deep Impact Extended mission in 2010. This correspondence suggests that interstellar objects can be significantly thermally processed before ejection into the interstellar medium, and by comparison to 1I and 2I, this processing can be widely variable in its physical outcome.
\n
Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx), a NASA Explorer satellite launched on 2025 March 11, is carrying out the first all-sky near-infrared spectral survey. The satellite observes in 102 spectral bands from 0.75 to 5.0 μm with a resolving power ranging from λ/Δλ = 35–130 in 6.\"2 pixels. The observatory obtains a 5σ depth of 19.5–19.9 AB mag for 0.75 < λ < 3.8 μm with λ/Δλ ∼ 40 and 17.8–18.8 AB mag for 3.8 < λ < 5.0 μm with λ/Δλ ∼ 120 after mapping the full sky four times over two years. Scientifically, SPHEREx will produce a large galaxy redshift survey over the full sky to constrain the amplitude of inflationary non-Gaussianity. The observations will produce two deep spectral maps near the ecliptic poles that use intensity mapping to probe the evolution of galaxies over cosmic history. By mapping the depth of infrared absorption features over the Galactic plane, SPHEREx will comprehensively survey the abundance and composition of water and other biogenic ice species in the interstellar medium. The project will release initial data rapidly in the form of spectral images, and specialized data products over the life of the mission as the surveys proceed. The science team will also produce spectral catalogs of planet-bearing and low-mass stars, solar system objects, and galaxy clusters three years after launch. We describe the design of the instrument and spacecraft, which flow from the core science requirements. Finally, we present an initial evaluation of the satellite’s in-flight performance and key characteristics.
",
"doi": "10.3847/1538-4357/ae2be2",
"issn": "0004-637X",
"publisher": "American Astronomical Society",
"publication": "Astrophysical Journal",
"publication_date": "2026-03-01",
"series_number": "1",
"volume": "999",
"issue": "1",
"pages": "139"
},
{
"id": "authors:zrg1z-qv096",
"collection": "authors",
"collection_id": "zrg1z-qv096",
"cite_using_url": "https://authors.library.caltech.edu/records/zrg1z-qv096",
"type": "article",
"title": "Improving H2RG Performance in SPHEREx Brassboard Model",
"author": [
{
"family_name": "Nguyen",
"given_name": "Chi H.",
"orcid": "0000-0001-9368-3186",
"clpid": "Nguyen-Chi-H"
},
{
"family_name": "Korngut",
"given_name": "Phillip",
"clpid": "Korngut-Philip-M"
},
{
"family_name": "Dowell",
"given_name": "C. Darren"
},
{
"family_name": "Bock",
"given_name": "James",
"orcid": "0000-0002-5710-5212",
"clpid": "Bock-J-J"
},
{
"family_name": "Burnham",
"given_name": "Jill",
"clpid": "Burnham-Jill-A"
},
{
"family_name": "Condon",
"given_name": "Samuel",
"orcid": "0000-0003-4255-3650",
"clpid": "Samuel-Condon"
},
{
"family_name": "Cook",
"given_name": "Walter",
"clpid": "Cook-Walter-Richardson-III"
},
{
"family_name": "Heaton",
"given_name": "Grigory",
"orcid": "0009-0003-5681-2956",
"clpid": "Heaton-Grigory-J"
},
{
"family_name": "Hui",
"given_name": "Howard",
"orcid": "0000-0001-5812-1903",
"clpid": "Hui-Howard"
},
{
"family_name": "Kecman",
"given_name": "Branislav",
"clpid": "Kecman-Branislav"
},
{
"family_name": "Miyasaka",
"given_name": "Hiromasa",
"orcid": "0000-0002-8074-4186",
"clpid": "Miyasaka-Hiromasa"
},
{
"family_name": "Manatt",
"given_name": "Kenneth"
},
{
"family_name": "Nguyen",
"given_name": "Hien T."
},
{
"family_name": "Padin",
"given_name": "Stephen",
"orcid": "0009-0001-9993-4393",
"clpid": "Padin-Stephen"
},
{
"family_name": "Viero",
"given_name": "Marco",
"orcid": "0000-0003-0545-4872",
"clpid": "Viero-Marco"
}
],
"abstract": "Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer is an upcoming NASA satellite mission to study the physics of inflation, the history of galaxy formation, and the abundance of biogenic ices in the Milky Way, obtaining the first all-sky spectroscopic survey at infrared wavelengths 0.75–5.0 μm. The instrument implements HAWAII-2RG (H2RG) detectors and custom-built Video8 electronics with multiple sampling features to optimize the H2RG noise performance, including nonsequential row reads, voltage monitoring, multiple visits to optically dark reference pixels, as well as onboard slope fitting and cosmic-ray removal. We report here the performance of a single H2RG with the readout electronics. We focus on the effectiveness of multiple reference samplings to reduce 1/f noise most relevant to the galaxy formation analysis, in particular the noise on large angular scales k <0.13 [pix−1] (∼5''–20'') where the imprints of galaxy clustering will be measured. Our characterization confirms that increased sampling of reference pixels successfully reduces the 1/f noise by ∼50% at these scales. However, the effectiveness of multiple reference reads is limited by irreducible per-pixel telegraph noise. Further noise reduction can be achieved by using optical pixels in addition to the reference pixels to remove common-mode signal offsets in each channel. Additionally, we observe that the gain of optical pixels is consistently ∼90% that of the reference pixels, prompting additional correction steps in the data reduction pipeline.
",
"doi": "10.3847/1538-4365/ad97bd",
"issn": "0067-0049",
"publisher": "American Astronomical Society",
"publication": "Astrophysical Journal Supplement Series",
"publication_date": "2025-02",
"series_number": "2",
"volume": "276",
"issue": "2",
"pages": "43"
}
]