IRAS 17449+2320: A Possible Binary System with the B[e] Phenomenon and a Strong Magnetic Field

We report the recent results of a long-term spectroscopic and photometric monitoring of IRAS 17449+2320, a member of the least studied group of objects with the B[e] phenomenon called FS CMa-type objects. The main hypothesis for explaining the strong emission-line spectra and infrared excesses of these objects assumes an ongoing or past mass transfer between the components in binary systems. The object is the only star with a gaseous and dusty envelope, where a strong and variable magnetic field (5.5–7.2 kG) was found through the splitting of some spectral lines. Additionally, we discovered the regular appearance of a red-shifted absorption component in spectral lines of neutral hydrogen, helium, and oxygen as well as one of ionized silicon with a period of 36.13 ± 0.20 days. We show that the magnetic field strength also followed this period. The process was accompanied by increasing emission component strengths for the hydrogen lines as well as the helium and metallic absorption lines. We refined the fundamental parameters of the optical counterpart of IRAS 17449+2320 (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi mathvariant="normal">T</mi><mi>eff</mi></msub><mo>=</mo><mn>9800</mn><mo>±</mo><mn>300</mn></mrow></semantics></math></inline-formula> K, log L/<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi mathvariant="normal">L</mi><mo>⊙</mo></msub><mo>=</mo><mn>1.86</mn><mo>±</mo><mn>0.06</mn></mrow></semantics></math></inline-formula>, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>v</mi><mo form="prefix">sin</mo><mi>i</mi><mo>=</mo><mn>9</mn><mo>±</mo><mn>2</mn></mrow></semantics></math></inline-formula> km s⁻¹) and concluded that the star was slightly metal-deficient and viewed nearly pole-on. No signs of a secondary component were found. Possible interpretations of the observed phenomena are suggested, and some earlier findings about the object’s nature are revised.