Period-luminosity relations, projection factors, and radii of anomalous Cepheids
Abstract
Context. Anomalous Cepheids (ACEPs) are radially pulsating stars observed in dwarf galaxies, the Galactic bulge and halo, and globular clusters. Similarly to other radially pulsating stars, they can be used as distance indicators through their period-luminosity relations (PLRs) and the geometrical Baade-Wesselink (BW) method. Aims. We aim to calibrate the zero point of the distance scale of ACEPs using nearby representatives of this class of pulsating stars. Methods. We collected optical/near-infrared photometry and spectra for a sample of nearby ACEPs with two telescopes located at the RolfChini Cerro Murphy Observatory (formerly Observatory Cerro Armazones) and optical telescopes offered by the Las Cumbres Observatory, along with instruments hosted and operated by the European Southern Observatory. Using parallaxes measured by the Gaia space mission and mean magnitudes from our new photometry, we calibrated the zero point of the period-luminosity relations (PLRs) in Johnson B , V , 2MASS J , H , K S , and Pan-STARRS g , r , i passbands, as well as select Wesenheit indices. The slopes were adopted from the PLRs of the LMC ACEPs from the literature. Using the surface brightness-color relation version of the BW technique, we were also able to determine the projection factors (p-factors) and mean radii of three nearby ACEPs. Results. The precision of the measured zero points is at the level of 0.04–0.05 mag and their systematic uncertainty was estimated to be about 0.1 mag. We used our zero point values and literature photometry related to LMC ACEPs to measure the distance modulus of this galaxy. We obtained a value of 18.454 ± 0.045 (statistical) mag, which is in very good agreement with the most accurate value from eclipsing binaries. The p-factors were 1.38 ± 0.13, 1.59 ± 0.21, and 1.35 ± 0.14 for V716 Oph, XX Vir, and UY Eri, respectively. We suspect that the very high p-factor of XX Vir results from the underestimated parallax of this star in the Gaia catalog, as its radius and absolute brightness are also higher than expected for ACEPs at this period. Finally, the radii measured for V716 Oph and UY Eri are in agreement with the period-radius relation obtained from LMC ACEPs.
Related
- Cepheid Metallicity in the Leavitt Law (C-MetaLL) survey: X First spectroscopic characterization of Galactic Type II Cepheids and calibration of the Period-Wesenheit-Metallicity relations
- Multi-chromatic observations of classical Cepheids using the CHARA Array interferometer: Surface brightness-colour relation, projection factor, and limb-darkening
- New Optical and Mid-Infrared RR Lyrae Period-Luminosity-Metallicity Relations for Precision Distances and Metallicity Distributions in the Magellanic Clouds
- H II region filling factors in NGC 628: Luminosity-size relation and connection with polycyclic aromatic hydrocarbon emission
- VELOcities of CEpheids (VELOCE) III. Reconstructing radial velocity curves of classical Cepheids
BibTeX
@article{wielgorski2026periodluminosity,
title = {{Period-luminosity relations, projection factors, and radii of anomalous Cepheids}},
author = {P. Wielgórski and G. Pietrzyński and W. Gieren and B. Zgirski and W. Narloch and G. Hajdu and J. Storm and Nicolas Nardetto and P. Kervella and B. Pilecki and M. Górski and R. Smolec and R. Salinas and D. Graczyk and V. Hocdé and P. Karczmarek and M. Taormina and W. Pych and H. Netzel and R. Chini and K. Hodapp and M. Kałuszyński and F. Pozo Nuñez and K. Kotysz and D. Moździerski and P. Mikołajczyk and P. Kołaczek-Szymański},
journal = {Astronomy \& Astrophysics - A\&A},
year = {2026},
month = jun,
doi = {10.1051/0004-6361/202659404},
eprint = {2603.28472},
archivePrefix = {arXiv},
url = {https://hal.science/hal-05791677v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Period-luminosity relations, projection factors, and radii of anomalous Cepheids
AU - P. Wielgórski
AU - G. Pietrzyński
AU - W. Gieren
AU - B. Zgirski
AU - W. Narloch
AU - G. Hajdu
AU - J. Storm
AU - Nicolas Nardetto
AU - P. Kervella
AU - B. Pilecki
AU - M. Górski
AU - R. Smolec
AU - R. Salinas
AU - D. Graczyk
AU - V. Hocdé
AU - P. Karczmarek
AU - M. Taormina
AU - W. Pych
AU - H. Netzel
AU - R. Chini
AU - K. Hodapp
AU - M. Kałuszyński
AU - F. Pozo Nuñez
AU - K. Kotysz
AU - D. Moździerski
AU - P. Mikołajczyk
AU - P. Kołaczek-Szymański
PY - 2026
DA - 2026/06/12
JO - Astronomy & Astrophysics - A&A
DO - 10.1051/0004-6361/202659404
UR - https://hal.science/hal-05791677v1
AB - Context. Anomalous Cepheids (ACEPs) are radially pulsating stars observed in dwarf galaxies, the Galactic bulge and halo, and globular clusters. Similarly to other radially pulsating stars, they can be used as distance indicators through their period-luminosity relations (PLRs) and the geometrical Baade-Wesselink (BW) method. Aims. We aim to calibrate the zero point of the distance scale of ACEPs using nearby representatives of this class of pulsating stars. Methods. We collected optical/near-infrared photometry and spectra for a sample of nearby ACEPs with two telescopes located at the RolfChini Cerro Murphy Observatory (formerly Observatory Cerro Armazones) and optical telescopes offered by the Las Cumbres Observatory, along with instruments hosted and operated by the European Southern Observatory. Using parallaxes measured by the Gaia space mission and mean magnitudes from our new photometry, we calibrated the zero point of the period-luminosity relations (PLRs) in Johnson B , V , 2MASS J , H , K S , and Pan-STARRS g , r , i passbands, as well as select Wesenheit indices. The slopes were adopted from the PLRs of the LMC ACEPs from the literature. Using the surface brightness-color relation version of the BW technique, we were also able to determine the projection factors (p-factors) and mean radii of three nearby ACEPs. Results. The precision of the measured zero points is at the level of 0.04–0.05 mag and their systematic uncertainty was estimated to be about 0.1 mag. We used our zero point values and literature photometry related to LMC ACEPs to measure the distance modulus of this galaxy. We obtained a value of 18.454 ± 0.045 (statistical) mag, which is in very good agreement with the most accurate value from eclipsing binaries. The p-factors were 1.38 ± 0.13, 1.59 ± 0.21, and 1.35 ± 0.14 for V716 Oph, XX Vir, and UY Eri, respectively. We suspect that the very high p-factor of XX Vir results from the underestimated parallax of this star in the Gaia catalog, as its radius and absolute brightness are also higher than expected for ACEPs at this period. Finally, the radii measured for V716 Oph and UY Eri are in agreement with the period-radius relation obtained from LMC ACEPs.
SN - 0004-6361
SN - 1432-0746
ER -