arXiv subjects

S. P. Jarvinen

Publications and source records attributed to S. P. Jarvinen.

At least 19 recordsLinked to original sources

arXiv2026

Star-Planet Interactions: The Instrumentation Perspective

Star-Planet Interactions (SPIs) produce observable phenomena across the electromagnetic spectrum, from X-ray and ultraviolet emission tracing magnetic activity and atmospheric escape to optical, infrared, and radio signatures probing stellar variability, planetary atmospheres, and magnetospheric interactions. This work reviews the current observational capabilities for SPI research, focusing on the instruments and facilities currently used, or technically capable of being used, for SPI studies. Particular emphasis is placed on the instrumental characteristics required to detect often weak and transient SPI signatures, as well as on the observational challenges associated with such measurements. The chapter concludes with an outlook on upcoming facilities that are expected to enhance our ability to detect, characterise, and understand SPI phenomena in the coming years.

astro-ph.IM↗

arXiv2026

Magnetic field detections in massive systems at different stages of interaction

Despite the importance of magnetic fields in massive stars, their origin is widely debated and still not well understood. With the mounting evidence for the importance of studying magnetic fields in interacting massive binary and multiple systems, it appears necessary to investigate the presence of magnetic fields in semi-detached systems with ongoing mass transfer, and in contact systems where mass is actively being exchanged. We present an analysis of 53 high-resolution HARPSpol spectropolarimetric observations of a sample of 14 massive binary and multiple systems using the least-squares deconvolution technique. The majority of the studied systems are classified as semi-detached or contact binaries. Definite detections of the presence of a magnetic field are achieved in all studied systems apart from the rather faint system SV Cen, for which only a marginal detection was obtained. The fact that the presence of magnetic fields is detected in all but one of the studied systems strongly suggests that interaction between the system components plays a definite role in the generation of magnetic fields in massive stars. The measured mean longitudinal magnetic field strength for all targets is of the order of a few hundred Gauss to a few kiloGauss. The strongest longitudinal magnetic fields of 4 to 5kG are discovered in the massive O-type triple system MY Ser in both components of the contact binary. kiloGauss-order magnetic fields are also detected in two other systems, V1294 Sco and V606 Cen. It is possible that there is an implication of some system characteristics, such as multiplicity, the mass ratio between the components, and a large fillout factor, on the measured magnetic field strength. Our results for the magnetic field measurements in interacting binaries present the first assessment of the occurrence rate of magnetic fields in a representative sample of such systems.

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arXiv2025

The enigmatic magnetic field of the planet hosting Herbig Ae/Be star HD169142

Recent observations of the accretion disk around the Herbig Ae/Be star HD169142 revealed its complex and asymmetric morphology indicating the presence of planets. The knowledge of the magnetic field structure in host stars is indispensable for our understanding of the magnetospheric interaction between the central stars, the circumstellar (CS) environment, and planetary companions. We intend to study the geometry of the magnetic field of HD169142. We measured the mean longitudinal magnetic field from high resolution ESPaDOnS and HARPSpol spectra of HD169142 using the Least Square Deconvolution technique. Additionally, the spectral variability of hydrogen lines is studied using dynamical spectra. Our analysis of the Stokes V spectra reveals the presence of definitely detected narrow Zeeman features observed using line masks with neutral iron lines. On two observing epochs, we also obtain marginally detected broad Zeeman features. To explain the simultaneous appearance of narrow and broad Zeeman features, we discuss different scenarios, including one scenario related to a non-photospheric origin of the narrow Zeeman features due to magnetospheric interaction with warm CS matter. In an environment such as a wind or an accretion disk, spectral lines may form over a relatively large volume, and the field topology may therefore be complex not only in latitude and azimuth, but in radius as well. Dynamical plots of the Hbeta line show an intriguing very complex structure with appearing and disappearing absorption features, which can be related to the complex morphology of the CS matter with asymmetric dust clump structures. The profiles of spectral lines belonging to different elements are variable, indicating the presence of chemical spots.

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arXiv2024

Detection of extragalactic magnetic massive stars

Studies of the magnetic characteristics of massive stars have recently received significant attention because they are progenitors of highly magnetised compact objects. Stars initially more massive than about 8M_sun leave behind neutron stars and black holes by the end of their evolution. The merging of binary compact remnant systems produces astrophysical transients detectable by gravitational wave observatories. Studies of magnetic fields in massive stars with low metallicities are of particular interest because they provide important information on the role of magnetic fields in the star formation of the early Universe. While several detections of massive Galactic magnetic stars have been reported in the last few decades, the impact of a low-metallicity environment on the occurrence and strength of stellar magnetic fields has not yet been explored. Because of the similarity between Of?p stars in the Magellanic Clouds (MCs) and Galactic magnetic Of?p stars, which possess globally organised magnetic fields, we searched for magnetic fields in Of?p stars in the MCs. Additionally, we observed the massive contact binary Cl* NGC 346 SSN7 in the Small Magellanic Cloud to test the theoretical scenario that the origin of magnetic fields involves a merger event or a common envelope evolution. We obtained and analysed measurements of the magnetic field in four massive Of?p stars in the MCs and the binary Cl* NGC 346 SSN7 using the ESO/VLT FORS2 spectrograph in spectropolarimetric mode. We detected kilogauss-scale magnetic fields in two Of?p-type stars and in the contact binary Cl* NGC 346 SSN7. These results suggest that the impact of low metallicity on the occurrence and strength of magnetic fields in massive stars is low. However, because the explored stellar sample is very small, additional observations of massive stars in the MCs are necessary.

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arXiv2024

Extreme Magnetic Field Modulus Variability of the Bp star HD 57372

Context. In chemically peculiar Ap/Bp stars with large-scale organised magnetic fields with a simple centred dipole configuration, the ratio between the maximum and the minimum of the mean magnetic field modulus is of the order of 1.25. Values of 2 or more are observed only for very few Ap/Bp stars and are indicative of a very unusual magnetic field geometry. Aims. Determining the magnetic field structure of Ap/Bp stars is bound to provide a different insight into the physics and the origin of the magnetic fields in early-type stars. In this respect, the Bp star HD 57372 is of particular interest because strongly variable magnetically split lines are observed in HARPS and APOGEE spectra. Methods. We obtained and analysed measurements of the mean magnetic field modulus and of the mean longitudinal magnetic field using near-infrared spectra and optical polarimetric spectra distributed over the stellar rotation period. Results. The mean magnetic field modulus of HD 57372, as estimated from absorption lines that are split via the Zeeman effect and resolved in both optical and near-infrared spectra, is found to vary by an extraordinary amount of about 10 kG. The exceptional value of 3 for the ratio between the maximum and the minimum of the field modulus is indicative of a very unusual geometry of HD 57372's magnetic field. All observable quantities are found to vary in phase with the photometric period of 7.889 days. This includes the longitudinal magnetic field , which varies from -6 kG up to 1.7 kG in FORS2 spectra as well as the metal line strengths, whose equivalent widths change by up to 50% of their mean values over the course of the rotation period. The B8 temperature class of HD 57372 also places it among the hottest stars known to exhibit resolved, magnetically split lines.

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arXiv2023

Searching for magnetic fields in pulsating A-type stars: the discovery of a strong field in the probable delta Sct star HD340577 and a null result for the gamma Dor star HR8799

Numerous delta Sct and gamma Dor pulsators are identified in the region of the Hertzsprung-Russell diagram that is occupied by chemically peculiar magnetic Ap stars. The connection between delta Sct and gamma Dor pulsations and the magnetic field in Ap stars is however not clear: theory suggests for magnetic Ap stars some critical field strengths for pulsation mode suppression by computing the magnetic damping effect for selected p and g modes. To test these theoretical considerations, we obtained PEPSI spectropolarimetric snapshots of the typical Ap star HD340577, for which delta Sct-like pulsations were recently detected in TESS data, and the gamma Dor pulsator HR8799, which is a remarkable system with multiple planets and two debris disks. Our measurements reveal the presence of a magnetic field with a strength of several hundred Gauss in HD340577. The measured mean longitudinal field would be the strongest field measured so far in a delta Sct star if the pulsational character of HD340577 is confirmed spectroscopically. No magnetic field is detected in HR8799.

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arXiv2023

Are magnetic fields universal in O-type multiple systems?

Although significant progress has been achieved in recent surveys of the magnetism in massive stars, the origin of the detected magnetic fields remains to be the least understood topic in their studies. We present an analysis of 61 high-resolution spectropolarimetric observations of 36 systems with O-type primaries, among them ten known particle-accelerating colliding-wind binaries exhibiting synchrotron radio emission. Our sample consists of multiple systems with components at different evolutionary stages with wide and tight orbits and different types of interactions. For the treatment of the complex composite spectra of the multiple systems, we used a special procedure involving different line masks populated for each element separately. Out of the 36 systems, 22 exhibit in their LSD Stokes V profiles definitely detected Zeeman features, among them seven systems with colliding winds. For fourteen systems the detected Zeeman features are most likely associated with O-type components whereas for three systems we suggest an association with an early B-type component. For the remaining five systems the source of the field is unclear. Marginal evidence for the detection of a Zeeman feature is reported for eleven systems and non-detection for three systems. The large number of systems with definitely detected Zeeman features presents a mystery, but probably indicates that multiplicity plays a definite role in the generation of magnetic fields in massive stars. The newly found magnetic systems are supreme candidates for spectropolarimetric monitoring over their orbital and rotation periods to obtain trustworthy statistics on the magnetic field geometry and the distribution of field strength.

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arXiv2022

The magnetic field of the stripped primary in the upsilon Sgr system, a member of the rare class of hydrogen-deficient binaries

We present the results of high-resolution spectropolarimetric observations of the optically dominant component in the rare hydrogen-deficient binary system upsilon Sgr. Only a small number of such systems in a very late phase of helium shell burning are currently known. The mass transfer from the donor star in binary systems usually leads to the stripping of its hydrogen envelope. Consequently, since the mass of the secondary increases, it appears rejuvenated. Using a few ESO FORS1 low-resolution spectropolarimetric observations of this system, Hubrig et al. announced in 2009 the presence of a magnetic field of the order of -70 - -80G. Here we report on more recent high-resolution ESO HARPS spectropolarimetric observations showing that the primary in upsilon Sgr is a spectrum variable star and possesses a weak magnetic field of the order of a few tens of Gauss. The detection of a magnetic field in this rare hydrogen-deficient binary is of particular interest, as such systems are frequently discussed as probable progenitors of core-collapse supernovae and gravitational-wave sources. Future magnetic studies of such systems will be worthwhile to gain deeper insights into the role of magnetic fields in the evolution of massive stars in binary systems.

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arXiv2021

The rapidly oscillating Ap star gamma Equ: linear polarization as an enhanced pulsation diagnostic?

We present the first short time scale observations of the roAp star gamma Equ in linear polarized light obtained with the PEPSI polarimeter installed at the LBT. These observations are used to search for pulsation variability in Stokes Q and U line profiles belonging to different elements. The atmospheres of roAp stars are significantly stratified with spectral lines of different elements probing different atmospheric depths. roAp stars with strong magnetic fields, such as gamma Equ with a magnetic field modulus of 4kG and a pulsation period of 12.21min, are of special interest because the effect of the magnetic field on the structure of their atmospheres can be studied with greatest detail and accuracy. Our results show that we may detect changes in the transversal field component in Fe I and rare-earth lines possessing large second-order Lande factors. Such variability can be due to the impact of pulsation on the transverse magnetic field, causing changes in the obliquity angles of the magnetic force lines. Further studies of roAp stars in linear polarized light and subsequent detailed modelling are necessary to improve our understanding of the involved physics.

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arXiv2020

The search for magnetic fields in two Wolf-Rayet stars and the discovery of a variable magnetic field in WR55

Magnetic fields in Wolf-Rayet (WR) stars are not well explored, although there is indirect evidence, e.g. from spectral variability and X-ray emission, that magnetic fields should be present in these stars. Being in an advanced stage of their evolution, WR stars have lost their hydrogen envelope, but their dense winds make the stellar core almost unobservable. To substantiate the expectations on the presence of magnetic fields in the most-evolved massive stars, we selected two WR stars, WR46 and WR55, for the search of the presence of magnetic fields using FORS2 spectropolarimetric observations. We achieve a formally definite detection of a variable mean longitudinal magnetic field of the order of a few hundred Gauss in WR55. The field detection in this star, which is associated with the ring nebula RCW78 and the molecular environment, is of exceptional importance for our understanding of star formation. No field detection at a significance level of 3sigma was achieved for WR46, but the variability of the measured field strengths can be rather well phased with the rotation period of 15.5h previously suggested by FUSE observations.

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arXiv2020

The near-infrared companion to HD94660 (=KQ Vel)

The Bp star HD94660 is a single-lined spectroscopic binary. Some authors have suggested that the unseen companion of at least 2M_sun may be a compact object. We intend to study this multiple system in detail, especially to learn more about the so-far unseen companion. We have collected and analyzed PIONIER H-band data from the Very Large Telescope Interferometer, TESS visible photometric data, and X-ray observations with Chandra of HD94660. Using PIONIER, we were able to detect the companion to HD94660, which is absent from high quality spectra at visible wavelengths, with a magnitude difference of 1.8 in the H band at a separation of 18.72mas. The TESS light curve shows variations with a period of 2.1d and also flaring. The Chandra spectrum is well described by emission from hot thermal plasma, yet might include a non-thermal component. The X-ray properties are compatible with a magnetically active companion, while some magnetospheric contribution from the primary is also possible. We can rule out that the companion to HD94660 is a compact source. It is also very unlikely that this companion is a single star, as the estimated mass of more than 2M_sun, the magnitude difference of 1.8 in the H band, and its non-detection in visible spectra are difficult to realize in a single object. One alternative could be a pair of late F stars, which would also be responsible for the detected photometric variations. Interferometric observations over the full binary orbit are necessary to determine the real mass of the companion and to add constraints on the overall geometry of the system.

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arXiv2020

Detection of weak magnetic fields in two HgMn stars

The main-sequence mercury-manganese (HgMn) stars are known to exhibit large overabundances of exotic elements and, similar to magnetic Ap/Bp stars, are spectrum variables, implying the presence of an inhomogeneous element distribution over the stellar surface. A number of magnetic field studies have been attempted in the last decades, indicating that magnetic fields in HgMn stars, if they exist, should be rather weak. The presence of tangled magnetic fields was suggested by several authors who detected quadratic magnetic fields using the moment technique. We employ the least-squares deconvolution technique to carry out a sensitive search for weak magnetic fields in spectropolarimetric observations of three HgMn stars, HD221507, HD65949, and HD101189, which have different fundamental parameters and spectral characteristics. A definite weak longitudinal field is discovered in HD221507 and HD65949 on single epochs, while only marginal field detections were achieved for HD101189. The new measurements indicate that the structure of the magnetic fields is probably rather complex: our analysis reveals the presence of reversed Stokes V profiles at the same observational epoch if individual elements are used in the measurements. This is the first observational evidence that individual elements sample distinct local magnetic fields of different polarity across the stellar surface.

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arXiv2019

The very slow rotation of the magnetic O9.7V star HD54879

The first FORS2 spectropolarimetric observation of the longitudinal magnetic field of HD54879 of the order of -600G with a lower limit of the dipole strength of ~2kG dates back to 2014. Since then observations showed a gradual decrease of the absolute value of the mean longitudinal magnetic field. In the course of the most recent monitoring of HD54879 using FORS2 spectropolarimetric observations from 2017 October to 2018 February, a longitudinal magnetic field strength change from about -300G down to about -90G was reported. A sudden increase of the absolute value of the mean longitudinal magnetic field and an accompanying spectral variability was detected on 2018 February 17. New FORS2 spectropolarimetric data obtained from 2018 December to 2019 February confirm the very slow magnetic field variability, with the field decreasing from about 150G to -100G over two months. Such a slow magnetic field variability, related to the extremely slow rotation of HD54879, is also confirmed using high-resolution HARPSpol and ESPaDOnS spectropolarimetry. The re-analysis of the FORS2 polarimetric spectra from 2018 February indicates that the previously reported field increase and the change of the spectral appearance was caused by improper spectra extraction and wavelength calibration using observations obtained at an insufficient signal-to-noise ratio. The presented properties of HD54879 are discussed in the context of the Of?p spectral classification.

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arXiv2019

The chemical composition of the Herbig Ae SB2 system AK Sco (HD152404)

We investigate the stellar atmospheres of the two components of the Herbig Ae SB2 system AK Sco to determine the elements present in the stars and their abundance. Equal stellar parameters T_eff = 6500K and log g = 4.5 were used for both stars. We studied HARPSpol spectra (resolution 110,000) that were previously used to state the presence of a weak magnetic field in the secondary. A composite synthetic spectrum was compared in the whole observed region lambda 3900-6912A with the observed spectrum. The abundances were derived mostly from unblended profiles, in spite of their sparsity, owing to the complexity of the system and to the not negligible v sin i of 18km/s and 21km/s adopted for the two components, respectively. The identified elements are those typical of stars with spectral type F5IV-V, except for Li I at 6707A and He I at 5875.61A, whose presence is related with the Herbig nature of the two stars. Furthermore, overabundances were determined in both stars for Y, Ba, and La. Zirconium is overabundant only in the primary, while sulfur is overabundant outside the adopted error limits only in the secondary. In contrast to previous results showing a high occurrence rate of lambda Boo peculiarities or normal chemical composition among the Herbig Ae/Be stars, the abundance pattern of AK Sco is similar to that of only few other Herbig stars displaying weak Ap/Bp peculiarities. A few accretion diagnostic lines are discussed.

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arXiv2019

A short and sudden increase of the magnetic field strength and the accompanying spectral variability in the O9.7V star HD54879

Only eleven O-type stars have been confirmed to possess large-scale organized magnetic fields. The presence of a -600G longitudinal magnetic field in the O9.7V star HD54879 with a lower limit of the dipole strength of ~2kG, was discovered a few years ago in the framework of the ESO large program "B-fields in OB stars". Our FORS2 spectropolarimetric observations from 2017 October 4 to 2018 February 21 reveal the presence of short and long-term spectral variability and a gradual magnetic field decrease from about -300G down to about -90G. Surprisingly, we discover on the night of 2018 February 17 a sudden, short-term increase of the magnetic field strength and measure a longitudinal magnetic field of -833G. The inspection of the FORS2 spectrum acquired during the observed magnetic field increase indicates a very strong change in spectral appearance with a significantly lower photospheric temperature and a decrease of the radial velocity by several 10km/s. Different scenarios are discussed in an attempt to interpret our observations. The FORS2 radial velocity measurements indicate that HD54879 is a member of a long-period binary.

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arXiv2018

Early B-type stars with resolved Zeeman split lines

Almost three decades ago, Mathys (1990) demonstrated the importance of studying Ap stars showing resolved Zeeman split Fe II 6147.7 and 6149.2 lines. Such Zeeman split lines can be seen in stars whose projected rotational velocity is sufficiently small and whose magnetic field is strong enough to exceed the rotational Doppler broadening. Observations of resolved Zeeman split lines permit the diagnosis of the average of the modulus of the magnetic field over the visible stellar hemisphere. Although Zeeman splitting is not expected in faster rotating hot massive stars, we have recently been discovering early B-type stars displaying magnetically split spectral lines.

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arXiv2018

Observations of magnetic fields in Herbig Ae/Be stars

Models of magnetically driven accretion reproduce many observational properties of T Tauri stars. For the more massive Herbig Ae/Be stars, the corresponding picture has been questioned lately, in part driven by the fact that their magnetic fields are typically one order of magnitude weaker. Indeed, the search for magnetic fields in Herbig Ae/Be stars has been quite time consuming, with a detection rate of about 7%, also limited by the current potential to detect weak magnetic fields. Over the last two decades, magnetic fields were found in about twenty objects and for only two Herbig Ae/Be stars was the magnetic field geometry constrained. Further, studies were undertaken to investigate the time dependence of spectroscopic tracers of magnetospheric accretion. Overall, it seems that while there is proof that magneospheric accretion is present in some Herbig Ae stars, there is less evidence for the Herbig Be stars.

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arXiv2018

Magnetic and pulsational variability of Przybylski's star (HD101065)

Since its discovery more than half a century ago Przybylski's star (HD101065) continues to excite the astronomical community by the unusual nature of its spectrum, exhibiting exotic element abundances. This star was also the first magnetic chemically peculiar A-type star for which the presence of rapid oscillations was established. Our analysis of newly acquired and historic longitudinal magnetic field measurements indicates that Przybylski's star is also unusual with respect to its extremely slow rotation. Adopting a dipolar structure for the magnetic field and using a sine wave fit to all reported longitudinal magnetic field values over the last 43yr, we find a probable rotation period P_rot ~ 188yr, which however has to be considered tentative as it does not represent a unique solution and has to be verified by future observations. Additionally, based on our own spectropolarimetric material obtained with HARPSpol, we discuss the impact of the anomalous structure of its atmosphere, in particular of the non-uniform horizontal and vertical distributions of chemical elements on the magnetic field measurements and the pulsational variability. Anomalies related to the vertical abundance stratification of Pr and Nd are for the first time used to establish the presence of a radial magnetic field gradient.

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