HR 5907 in Band 2

Science Target Overview

HR 5907 is a main-sequence B2.5 V star with a rotational period of 0.508276 days. It is the brightest known early-type star in the cm–mm band (approximately 100–130 mJy/beam at 100 GHz) and possesses a strong magnetic field that shows variability at the rotation period. The source shows frequency-dependent levels of circular polarization from 2 to 44 GHz, with ∼8% circular polarization at 44 GHz (Leto et al. 2018).

The strong circularization polarization fraction and its frequency dependence make it ideal to verify the capability the wideband receiver Band 2 to detect changes in the polarization fraction within the band range.

ALMA Data Overview

Observations were carried out on the 24th of November 2025 with 23 antennas and for a total on-source time of about 70 minutes. The typical PWV during observations was 0.4-0.65 mm. The baseline lengths range from 15 m to 2.4 km. In total, four spectral windows of 1.875 GHz were used to cover the 68-92 GHz frequency range.

Calibration and imaging were performed using the ALMA pipeline in a standard manner, including the standard mitigation parameter of the pipeline to generate the images. No self-calibration has been applied to the data. Auto-masking was used for generating the images unless indicated otherwise.

Some additional flagging and intervention in the pipeline were needed as follows: we excluded the step "polcalflag" in the pipeline as it was adding unnecessary flags in one of the Execution Blocks preventing the polarization calibration to proceed. Excluding this step, the calibration of both total intensity and polarization proceeded smoothly, and the results on the polarization calibrator are consistent with those reported for Band 3 in the AMAPOLA monitoring campaign. In addition, we noted some higher phase vs frequency values in the phase calibrator in one antenna, but they do not affect the data calibration quality.

Note: the flux calibration for Band 2 data is still being refined. The flux.csv table provided in the calibration folders needs to be used, as it provides the best values retrieved through a curvature fitting of the calibrator source at the other ALMA bands.

The continuum emission is clearly detected in the image and the achieved rms is 0.0131 mJy/beam for a beam of 0.891x0.411 arcsecs and a bandwidth of 7.5GHz at a frequency of 74.9000 GHz. The Stokes images of the calibrator and the target, both in continuum and line mode, have been obtained using the standard pipeline. No linear polarization is detected in the target, but a Stokes V emission, corresponding to ~14% of Stokes I, is clearly detected. This detection is well above the 1.8% Stokes V, the 3-sigma accuracy of the calibration currently assured by ALMA.

Using the data for publication

The following statement should be included in the acknowledgement of papers using the dataset listed above:

"This paper makes use of the following ALMA data: ADS/JAO.ALMA#2011.0.00023.SV. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada) and MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ."

Obtaining the Data

The data products are contained in the following directory:

Parent directory for download

The above directory contains README, uncalibrated data, calibrated data, data reduction and imaging scripts, and reference images.