About

Christopher Stubbs is the Samuel C. Moncher Professor of Physics and of Astronomy at Harvard University. He is an experimental physicist working at the interface between particle physics, cosmology, and gravitation. His research interests include experimental tests of the foundations of gravitational physics, searches for dark matter, characterizing dark energy, and observational cosmology. Stubbs was a member of one of the two teams that first discovered dark energy by using supernovae to map out the history of cosmic expansion. He is heavily engaged in the construction of the Large Synoptic Survey Telescope (LSST), for which he served as the inaugural project scientist. Additionally, he founded the APOLLO collaboration, which uses lunar laser ranging and the Earth-Moon-Sun system to probe for novel gravitational effects that may result from physics beyond the standard model. His work involves experimental efforts to understand fundamental aspects of the universe, contributing significantly to the fields of astrophysics and cosmology.

Research topics

• Computer Science
• Physics
• Astronomy
• Remote sensing
• Geology
• Astrophysics
• Mathematical physics
• Computer graphics (images)
• Environmental science
• Geodesy
• Statistics

Selected publications

• DAmodel: hierarchical Bayesian modelling of DA white dwarfs for spectrophotometric calibration

  Monthly Notices of the Royal Astronomical Society · 2025-04-16 · 4 citations

  articleOpen access

  ABSTRACT We use hierarchical Bayesian modelling to calibrate a network of 32 all-sky faint DA white dwarf (DA WD) spectrophotometric standards ($16.5 < V < 19.5$) alongside three CALSPEC standards, from 912 Å to 32 $\mu$m. The framework is the first of its kind to jointly infer photometric zero points and WD parameters (surface gravity $\log g$, effective temperature $T_{\text{eff}}$, extinction $A_V$, dust relation parameter $R_V$) by simultaneously modelling both photometric and spectroscopic data. We model panchromatic Hubble Space Telescope Wide Field Camera 3 (HST/WFC3) UVIS and IR photometry, HST/STIS UV spectroscopy, and ground-based optical spectroscopy to sub-per cent precision. Photometric residuals for the sample are the lowest yet yielding $<0.004$ mag RMS on average from the UV to the NIR, achieved by jointly inferring time-dependent changes in system sensitivity and WFC3/IR count-rate nonlinearity. Our GPU-accelerated implementation enables efficient sampling via Hamiltonian Monte Carlo, critical for exploring the high-dimensional posterior space. The hierarchical nature of the model enables population analysis of intrinsic WD and dust parameters. Inferred spectral energy distributions from this model will be essential for calibrating the James Webb Space Telescope as well as next-generation surveys, including Vera Rubin Observatory’s Legacy Survey of Space and Time and the Nancy Grace Roman Space Telescope.

  PublisherOA PDFDOI

• PANDORA: new avenues in sub-percent photometric precision for ground-based astronomy

  2025-08-01

  articleSenior author

  Precision photometric calibration is key to a number of astrophysical research areas such as supernova cosmology and dark energy studies. In the age of large surveys, pushing the limits of photometry is a worthy challenge, with traditional celestial calibrators limited to approximately percent precision. Here we present PANDORA, a novel calibration source that achieves sub-percent photometric precision across the optical spectrum with a selectable dynamic range and high optical efficiency. Building on proven collimated beam projector designs for relative throughput calibration of survey telescopes, PANDORA is capable of delivering photons anywhere in the 350-1100 nm spectral range. It uses selectable neutral density filters and sequential NIST-calibrated photodiode feedback to internally self-calibrate prior to operation, and is illuminated by an Energetiq EQ-99XFC broadband laser-driven light source. We present here; an overview of the system design, operation, and laboratory characterization results. PANDORA will begin science operations this year to support the upcoming LS4 survey on the ESO 1m Schmidt telescope.

  PublisherDOI

• Measuring Local Turbulence Along the Optical Path: Multi-Beam Optical Seeing Sensor

  Journal of Astronomical Instrumentation · 2025-09-04

  articleSenior author

  Deflection of light along the optical path is a major source of image degradation for ground-based telescopes. Methods have been developed to measure upper atmospheric seeing based on models of the turbulence in the atmosphere, but due to boundary conditions, transmission within telescope enclosures is more complex. The Multi-beam Optical Seeing Sensor (MOSS) directly measures the component of the image quality degradation from inhomogeneity of the index of refraction within the telescope dome. MOSS outputs four near-parallel beams of light that travel along the optical path and are imaged by the telescope’s detector, landing like starlight on the telescope’s focal plane. By using a strobed light source, we can ‘freeze’ the instantaneous index variations transverse to the optical path. This system captures both ‘dome’ and ‘mirror’ seeing. Through plotting the standard deviation of differential motion between pairs of beams, MOSS enables characterization of the length scale of turbulence within the dome. The temporal coherence of temperature gradients can be probed with different pulse lengths, and the spatial coherence by comparing pairs at different separations across the aperture of the telescope. Optical path turbulence measurements, alongside other telemetry metrics, will guide thermal and airflow management to optimize image quality. A MOSS prototype was installed in the 1.2[Formula: see text]m Auxiliary Telescope (AuxTel) at the Vera C. Rubin Observatory in Chile, and preliminary data constrain the optical path turbulence with a lower bound of 1.4 arcsec. The optical path turbulence varied throughout the night of observing.

  PublisherDOI

• Measuring Local Turbulence Along the Optical Path: Multi-beam Optical Seeing Sensor (MOSS)

  ArXiv.org · 2025-08-01

  preprintOpen accessSenior author

  Deflection of light along the optical path is a major source of image degradation for ground-based telescopes. Methods have been developed to measure upper atmospheric seeing based on models of the turbulence in the atmosphere, but due to boundary conditions, transmission within telescope enclosures is more complex. The Multi-beam Optical Seeing Sensor (MOSS) directly measures the component of the image quality degradation from inhomogeneity of the index of refraction within the telescope dome. MOSS outputs four near-parallel beams of light that travel along the optical path and are imaged by the telescope's detector, landing like starlight on the telescope's focal plane. By using a strobed light source, we can 'freeze' the instantaneous index variations transverse to the optical path. This system captures both 'dome' and 'mirror' seeing. Through plotting the standard deviation of differential motion between pairs of beams, MOSS enables characterization of the length scale of turbulence within the dome. The temporal coherence of temperature gradients can be probed with different pulse lengths, and the spatial coherence by comparing pairs at different separations across the aperture of the telescope. Optical path turbulence measurements, alongside other telemetry metrics, will guide thermal and airflow management to optimize image quality. A MOSS prototype was installed in the 1.2 meter Auxiliary Telescope (AuxTel) at the Vera C. Rubin Observatory in Chile, and preliminary data constrain the optical path turbulence with a lower bound of 1.4 arcseconds. The optical path turbulence varied throughout the night of observing.

  PublisherOA PDFDOI

• The La Silla Schmidt Southern Survey

  Publications of the Astronomical Society of the Pacific · 2025-09-01 · 8 citations

  articleOpen access

  Abstract We present the La Silla Schmidt Southern Survey (LS4), a new wide-field, time-domain survey to be conducted with the 1 m ESO Schmidt telescope. The 268 megapixel LS4 camera mosaics 32 2k × 4k fully depleted CCDs, providing a ∼20 deg 2 field of view with 1 ″ pixel −1 resolution. The LS4 camera will have excellent performance at longer wavelengths: in a standard 45 s exposure the expected 5 σ limiting magnitudes in g , i , z are ∼21.5, ∼20.9, and ∼20.3 mag (AB), respectively. The telescope design requires a novel filter holder that fixes different bandpasses over each quadrant of the detector. Two quadrants will have i band, while the other two will be g and z band with color information obtained by dithering targets across the different quadrants. The majority (90%) of the observing time will be used to conduct a public survey that monitors the extragalactic sky at both moderate (3 days) and high (1 day) cadence, as well as focused observations within the Galactic plane and bulge. Alerts from the public survey will be broadcast to the community via established alert brokers. LS4 will run concurrently with the Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST). The combination of LS4+LSST will enable detailed holistic monitoring of many nearby transients: high-cadence LS4 observations will resolve the initial rise and peak of the light curve while less-frequent but deeper observations by LSST will characterize the years before and after explosion. Here, we summarize the primary science objectives of LS4 including microlensing events in the Galaxy, extragalactic transients powered by massive black holes or stellar explosions, the search for electromagnetic counterparts to multi-messenger events, and supernova cosmology.

  PublisherOA PDFDOI

• Discovery of Small-Molecule Ligands for the E3 Ligase STUB1/CHIP from a DNA-Encoded Library Screen

  ACS Medicinal Chemistry Letters · 2025-08-05 · 4 citations

  articleOpen access

  STIP1 homology and U-box containing protein 1 (STUB1), also known as the C-terminus of Hsc70-interacting protein (CHIP), is an E3 ligase that plays a crucial role in removal of misfolded proteins via Hsc70. A DEL screen was run against CHIP to identify small-molecule binders. Two hits were identified that were confirmed by biochemical and biophysical techniques, including 2D NMR. X-ray crystal structures were obtained, which revealed binding to the peptide binding site. Fragment-based deconstruction indicated that hit 2 was a suitable starting point for optimization. During the optimization, an unexpected rearrangement of an oxadiazole from an array hit led to the exploration of an amide vector. This resulted in the discovery of compound 5, which is the most potent small-molecule ligand for CHIP identified to date and a suitable starting point for further optimization into a tool molecule or PROTAC warhead.

  PublisherOA PDFDOI

• Modification and validation of the Bluebelle Wound Healing Questionnaire (WHQ) for assessing surgical site infection in wounds healing by secondary intention

  Journal of Tissue Viability · 2025-03-18 · 1 citations

  articleOpen access

  Surgical wounds healing by secondary intention are common. Healing is often complicated by surgical site infection (SSI). SSI assessment is important to guide treatment but existing methods generally require in-person assessment, making them resource intensive. A validated patient-reported SSI outcome measure may be useful to overcome this limitation. To modify and validate the Bluebelle Wound Healing Questionnaire (WHQ) for wounds healing by secondary intention. The 18-item Bluebelle WHQ developed for wounds healing by primary intention was modified to make it applicable to secondary healing wounds. Testing was performed as part of the SWHSI-2 randomised trial assessing negative pressure wound dressings versus standard care. Participants completed the WHQ at five timepoints; in-person (baseline, post-healing) and by post (3, 6, 12 months). A reference SSI assessment was performed by a research nurse at the time of wound healing. Acceptability and criterion validity (ability of the Bluebelle WHQ to discriminate between SSI/no SSI) were explored by examining questionnaire return rates, levels of missing data and total score sensitivity/specificity values (receiver operating characteristic curve (ROC)). Baseline in-person questionnaire return rates were highest (672/686; 98 %), with postal return rates of 428/615 (68.5 %), 274/416 (65.9 %) and 186/296 (62.8 %) at follow up points. Overall, low levels of item-missing data were observed with few problems completing the questionnaire reported. Ability to discriminate between SSI/no SSI was good (Area under ROC = 0.796). The modified Bluebelle WHQ is a valuable tool for post-discharge assessment of wounds healing by secondary intention. It is recommended for use in research and clinical practice. • Validation of a modified version of the Bluebelle Wound Healing Questionnaire (WHQ) in wounds healing by secondary intention. • The tool is acceptable to patients with good criterion validity compared to existing methods for SSI assessment. • This is the first validated patient-reported tool for assessing SSI in wounds healing by secondary intention. • It is suitable for use in research and clinical practice.

  PublisherDOI

• StarDICE III: characterization of the photometric instrument with a collimated beam projector

  RAS Techniques and Instruments · 2025-01-01 · 1 citations

  articleOpen access

  ABSTRACT The measurement of Type Ia supernovae magnitudes provides cosmological distances, which constrain dark energy parameters. Current and upcoming large photometric surveys require improved photometric calibration precision to reduce systematic uncertainties in cosmological constraints. The StarDICE experiment aims to establish accurate broad-band flux references for these surveys, targeting sub-percent precision in magnitude measurements. Achieving this requires precise filter bandpass measurements for both StarDICE and survey instruments with sub-nanometre accuracy. To this end, we developed the Collimated Beam Projector (CBP), an optical device for calibrating the throughput of astronomical telescopes and their filters. The CBP uses a tunable laser source and a reversed telescope to emit a parallel monochromatic light beam, continuously monitored in flux and wavelength. The CBP output flux is measured with a large-area photodiode calibrated relative to a NIST photodiode. Using CBP measurements, we derive the StarDICE telescope throughput and filter transmissions, anchoring them to NIST’s absolute calibration. After analysing systematic uncertainties, we achieved sub-nanometre accuracy for filter central wavelengths, measured filter transmission with ~0.5 per cent precision per $1 \,{\rm nm}$ bin, and detected out-of-band leakages at a relative level of $10^{-4}$. Furthermore, we synthesized equivalent transmission for full pupil illumination from four sampled positions in the StarDICE telescope mirror, with ~$0.2 \,{\rm nm}$ accuracy for central wavelengths and $7 \,{\rm mmag}$ for broad-band fluxes. This demonstrates our ability to characterize telescope throughput down to the millimagnitude, paving the way for future developments, such as the Rubin-CBP for measuring the LSST at Vera Rubin Observatory, and a portable CBP version for in-situ transmission monitoring.

  PublisherOA PDFDOI

• Abstract ND11: AZD0022: a potent, oral KRASG12D-selective inhibitor that drives robust pathway inhibition and anti-tumour activity in KRASG12D models

  Cancer Research · 2025-05-22 · 4 citations

  article

  Abstract The small GTPase KRAS is frequently mutated in cancer and KRASG12D is its most common mutation, with ∼34% incidence in pancreatic ductal adenocarcinoma (PDAC), ∼12% in colorectal cancer (CRC) and ∼4% in non-small cell lung cancer (NSCLC). KRASG12D mutations disrupt the GTPase activity of the protein, resulting in elevated cellular levels of active, GTP-bound KRASG12D. KRASG12D mutations are therefore associated with increased and deregulated RAS signalling, driving uncontrolled cell proliferation and survival. Despite major advances in RAS-targeting in recent years, KRASG12D-cancers continue to represent an unmet medical need. AZD0022 is a potent, orally bioavailable, KRASG12D-selective reversible inhibitor with the potential to provide therapeutic benefit to patients with KRASG12D-mutated cancers. AZD0022 shows high affinity to both the active (KRASG12D-GTP) and inactive forms of KRASG12D (KRASG12D-GDP) protein by Surface Plasmon Resonance, and selectivity over wild-type KRAS. AZD0022 treatment drives robust and concentration-dependent biomarker inhibition in KRASG12D CRC, PDAC and NSCLC models in vitro and in vivo and inhibits proliferation and viability of KRASG12D-tumour cells across these indications. Following oral administration in mouse, rat and dog, AZD0022 exhibited significant oral exposure and long terminal elimination phase half-life values. Oral, chronic daily treatment of a panel of CRC, PDAC and NSCLC CDX (cell line-derived xenograft) and PDX (patient-derived xenograft) models with AZD0022 demonstrated broad anti-tumour activity of AZD0022 across KRASG12D-mutant tumour types. The therapeutic responses of KRASG12D CRC and PDAC models to AZD0022 were further improved by cetuximab combination treatment, with sustained regressions observed in both tumour types. Together, the pre-clinical pharmacology of AZD0022 supports its oral anti-tumor activity and KRASG12D-selectivity and shows that it has the potential to improve outcomes for patients with KRASG12D mutated cancers, either as monotherapy or in combination with other agents. AZD0022 is currently being investigated in the ALAFOSS-01 (NCT06599502) study, a first-in-human, open-label, multicenter, phase 1/2a study of AZD0022 in patients with KRASG12D-mutated solid tumors. Citation Format: Carla P. Martins, Alex Koers, Sreyoshi Mitra, Alison Peter, Katie Young, Christopher Chambers, Zoe Underwood, Kevin Beaumont, Sofia Guzzetti, Christopher Stubbs, Derek Barratt, Benjamin Phillips, Eleanor Wigmore, Melissa Chapman, Michele Moschetta, Simon Barry, Susan Critchlow, Michael Niedbala. AZD0022: a potent, oral KRASG12D-selective inhibitor that drives robust pathway inhibition and anti-tumour activity in KRASG12D models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_2):Abstract nr ND11.

  PublisherDOI

• GW190425: Pan-STARRS and ATLAS coverage of the skymap and limits on optical emission associated with FRB 20190425A

  Monthly Notices of the Royal Astronomical Society · 2024-01-12 · 19 citations

  articleOpen access

  ABSTRACT GW190425 is the second of two binary neutron star (BNS) merger events to be significantly detected by the Laser Interferometer Gravitational Wave (GW) Observatory (LIGO), Virgo and the Kamioka Gravitational Wave (KAGRA) detector network. With a detection only in LIGO Livingston, the skymap containing the source was large and no plausible electromagnetic counterpart was found in real-time searching in 2019. Here, we summarize Asteroid Terrestrial-Impact Last Alert System (ATLAS) and Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) wide-field optical coverage of the skymap beginning within 1 and 3 h, respectively, of the GW190425 merger time. More recently, a potential coincidence between GW190425 and a fast radio burst FRB 20190425A has been suggested, given their spatial and temporal coincidences. The smaller sky localization area of FRB 20190425A and its dispersion measure led to the identification of a likely host galaxy, UGC 10667 at a distance of 141 ± 10 Mpc. Our optical imaging covered the galaxy 6.0 h after GW190425 was detected and 3.5 h after the FRB 20190425A. No optical emission was detected and further imaging at +1.2 and +13.2 d also revealed no emission. If the FRB 20190425A and GW190425 association were real, we highlight our limits on kilonova emission from a BNS merger in UGC 10667. The model for producing FRB 20190425A from a BNS merger involves a supramassive magnetized neutron star spinning down by dipole emission on the time-scale of hours. We show that magnetar-enhanced kilonova emission is ruled out by optical upper limits. The lack of detected optical emission from a kilonova in UGC 10667 disfavours, but does not disprove, the FRB–GW link for this source.

  PublisherOA PDFDOI

Recent grants

• Collaborative Research: Coordinated Surveys to Study the Nature of the Dark Energy.

  NSF · $35k · 2005–2010

• Probing the Equation of State of the Dark Energy with Supernovae.

  NSF · $1.9M · 2005–2010

• Collaborative Research: Optical Confirmation, Redshifts, and Richness for Galaxy Clusters Discovered with the South Pole Telescope

  NSF · $998k · 2010–2015

Frequent coauthors

• K. Griest

  Laboratory for Atmospheric and Space Physics

  515 shared

• M. R. Pratt

  University of Utah

  420 shared

• C. Alcock

  Center for Astrophysics Harvard & Smithsonian

  396 shared

• K. C. Freeman

  North Carolina Central University

  368 shared

• B. A. Peterson

  Mount Stromlo Observatory

  360 shared

• K. H. Cook

  Southern Illinois University Carbondale

  331 shared

• M. J. Lehner

  326 shared

• D. P. Bennett

  324 shared