Bipolar jets from KX And

Bipolar jets with an apparent length of 20′ ejected from KX And (Andromedae) have been discovered in the first data release of the Northern Sky Narrowband Survey. KX And is a well-studied interacting binary with mass transfer through Roche lobe overflow in a distance of about 760 pc. However, the faint jets, have been overlooked in the past. With a known inclination of about 50° of the binary system, this leads to a true length of the jets of about 19 light-years (5.8 pc) in each direction.

Results

Hα  [OIII] [SII]

Hα  [OIII]  [SII]

Hα [OIII]  [SII]

Hα Photon flux estimations for selected regions can be found in Ziegenbalg (2024).

Nature of the jets

KX And (also known as BD+49 4045 and HD 218393) is a binary system consisting in a primary star with a spectral classification of B3pe and a cool giant of type K1III (Shenavrin et al., 2011). This secondary star, which has about half the mass of its companion (Floquet et al., 1995), is assumed to overflow its Roche lobe and thus transferring gas to the primary star (Floquet et al., 1989). The resulting accretion disk is responsible for the emission lines in the spectrum of the Be star.

A fraction of the material that falls to the accreting star is ejected in the form of jets which are aligned perpendicular to the accretion disk. The jets cannot be detected in [OIII] and are likely ionized by the B3pe component of KX And. The elongated shell, including the bright tip at the end of the northern jet, is probably formed by the interaction of the ejected gas with the interstellar medium and may be rendered visible through shock ionization. Parts of the shell are visible at all observed wavelengths.

The apparent length of the northern jet (with the bright tip) is 19.9′, while the southern jet is 20.3′ long. With a distance of 760±10 pc (Gaia Collaboration et al., 2023) and an inclination to the line of sight of the binary system (and thus of the accretion disc) of about 50° (Berdyugin et al., 1998), this corresponds to a true length of about 19 light-years (5.8 pc) for each jet.

Comparison with other jets from binaries

Several other mass transferring binaries that eject jets have been observed in the past. One class contains a white dwarf or sub-dwarf and a red giant, losing mass through the stellar wind. These systems are called symbiotic stars. (The definition of this term is not uniform. Some authors classify Roche lobe overflowing stars like KX And also as symbiotic star.) The most famous example of this group is likely R Aqr, which is assumed to contain a Mira-type variable and a white dwarf. The jet ejected by this system is embedded in a complex nebula ionized by the white dwarf. The apparent size of the jets is about 75″ (Liimets et al., 2018). With a distance of about 218 pc (Minet al., 2014) and a inclination of about 70° Gromadzki and Mikolajewska, 2009) this corresponds to a true size of about 0.3 light-years, less than 2% of the length of the KX And jets.

Another class of mass-transferring systems is X-ray binaries, which consist in a mass donating star and an accreting neutron star or black hole. The infalling material releases energy as X-rays, giving these binaries their name. The most famous example is Cyg X-1, a binary consisting in a black hole and the supergiant HD 226868 of spectral class O7Iab (Sota et al., 2011). It is assumed that this star does not overflow its Roche lobe (Ziolkowski, 2014), i.e. mass is transferred through stellar wind.

In optical wavelengths, only one jet becomes visible indirectly due to the interaction of high-energy particles with surrounding interstellar medium. The apparent separation between the resulting shockwave and the binary is 10.9′ (measured in own images). Assuming the jet ends at the bow shock, distance measurements from Gaia DR3 (2255±80 pc) and a inclination of about 27.5° for the binary system (Zdziarski et al., 2024) result in a true length of about 51 light-years. The authors of the latter publication also discuss the possibility of a tilted inner accretion disc with a inclination of 39°, which would result in a length of 37 light-years.

Although the jet of this reference X-ray binary appears to be significantly more energetic, the size of the newly discovered jets from KX And is on the same order of magnitude as that of the jet ejected from Cyg X-1.

Image and instrument data

Position (J2000):	RA: 23h07m06.21s; DEC: 50°11′32.5″ (centered on KX And)
Image width × height:	40′ × 30′
Orientation:	North is oriented upward, but rotated 3.5° toward east (left)
Date:	Oct. 25 to Feb. 2026
Location:	Pulsnitz, Germany
Instrument:	400mm Newton at f=1520mm
Camera Sensor:	Sony IMX455
Total exposure times:	H-alpha (3.5 nm): 23.7 h [OIII] (3 nm): 40.5 h [SII] (3 nm): 40.7 h Continuum (SDSS I'): 4.9 h Continuum (SDSS B'): 4.9 h (This statistic includes only the images that were used. Approximately 30% of all images were rejected because of poor resolution caused by unusually bad seeing in 2025.).

Image processing

The images — especially the [OIII] and [SII] channels — suffer from a low signal to noise ratio. Denoising parameters have been chosen carefully to preserve details as much details as possible, but also resulting in artifacts caused by residual noise. No manual retouching was performed, all image-processing steps are deterministic, and none of the algorithms use machine learning (often referred to as “AI”), which tends to generate plausible-looking but artificial details. The software used can be downloaded here.

The individual exposures were aligned and intensity-calibrated to sources form Gaia DR3 using synthetic photometry. The Stacking was performed with weights based on noise estimation in order to maximize the final signal-to-noise ratio.

Emission line images are obtained from the stacked results through continuum subtraction. To avoid artifacts around stars, this was done in two steps. First, the stars are subtracted by extracting their positions and intensities from the continuum image. Then, the (starless) residuals are subtracted. This procedure prevents small structures, such as the knots in the jets, from being misinterpreted as stars and therefore removed. Another consequence (of determination the star brightness from the continuum images) is that the emission-line star KX And is only partially subtracted in Hα.

The continuum-subtracted images are then deconvolved and denoised. These results are used to create both color and monochrome images. For the color images, a luminance image is first created by a linear combination of the emission line channels, then tonal curve adjusted, and finally colorized using the linear emission line channels. The last step is designed to preserve luminance, i.e. if one color channel becomes saturated, the intensities in the other channels are increased to maintain the luminance. This prevents loss of detail in saturated regions and is also the reason why KX And appears white rather than green, even though this emission-line star is mainly visible in Hα.

Citing / persistent resources

If referencing this volatile webpage is not appropriate, a RNASS article is available via the DOI 10.3847/2515-5172/ad9478.

References

 

V. I. Shenavrin, O. G. Taranova, and A. E. Nadzhip. Search for and study of hot circumstellar dust envelopes. Astronomy Reports, 55(1):31–81, January 2011. [ DOI | .pdf ]

 

M. Floquet, A. M. Hubert, H. Hubert, D. Ballereau, and J. Chauville. The binary system of the Be star KX Andromedae. A&A, 294:227–231, February 1995. [ http ]

 

M. Floquet, A. M. Hubert, J. P. Maillard, J. Chauville, and H. Chatzichristou. Search for cool giant companions of the Be stars zeta Tau and KX And. A&A, 214:295–303, April 1989. [ http ]

 

Gaia Collaboration et al. Gaia data release 3 - summary of the content and survey properties. A&A, 674:A1, 2023. [ DOI | http ]

 

A. V. Berdyugin, S. V. Berdyugina, and A. E. Tarasov. New photometric and polarimetric observations of the massive interacting binary KX And. Astronomy Letters, 24(3):309–315, May 1998. [ http ]

 

Liimets, T., Corradi, R. L. M., Jones, D., Verro, K., Santander-García, M., Kolka, I., Sidonio, M., Kankare, E., Kankare, J., Pursimo, T., and Wilson, P. A. New insights into the outflows from r aquarii. A&A, 612:A118, 2018. [ DOI | http ]

 

Cheulhong Min, Naoko Matsumoto, Mi Kyoung Kim, Tomoya Hirota, Katsunori M. Shibata, Se-Hyung Cho, Makoto Shizugami, and Mareki Honma. Accurate parallax measurement toward the symbiotic star r aquarii. Publications of the Astronomical Society of Japan, 66(2), April 2014. [ DOI | http ]

 

M. Gromadzki and J. Mikolajewska. The spectroscopic orbit and the geometry of R Aquarii. A&P, 495(3):931–936, March 2009. [ DOI | arXiv ]

 

A. Sota, J. Maíz Apellániz, N. R. Walborn, E. J. Alfaro, R. H. Barbá, N. I. Morrell, R. C. Gamen, and J. I. Arias. The Galactic O-Star Spectroscopic Survey. I. Classification System and Bright Northern Stars in the Blue-violet at R ˜ 2500. ApJs, 193(2):24, April 2011. [ DOI | arXiv ]

 

J. Ziolkowski. Determination of the masses of the components of the HDE 226868/Cyg X-1 binary system. MNRAS, 440:L61–L65, May 2014. [ DOI | arXiv | http ]

 

Andrzej A. Zdziarski, Swadesh Chand, Srimanta Banerjee, Michal Szanecki, Agnieszka Janiuk, Piotr Lubiński, Andrzej NiedŹwiecki, Gulab Dewangan, and Ranjeev Misra. What Is the Black Hole Spin in Cyg X-1? ApJL, 967(1):L9, May 2024. [ DOI | arXiv | http ]

 

Stefan Ziegenbalg. Detection of 19 lt-yr long bipolar jets from interacting binary kx and. Research Notes of the AAS, 8(11):289, nov 2024. [ DOI | http ]