Context. We trace several dusty infrared sources on their orbits around Sgr A* with SINFONI and NACO mounted at the VLT/Chile. These sources show near-infrared excess and Doppler-shifted line emission. We investigate these sources in order to clarify their nature and compare their relationship to other observed NIR objects close to Sgr A*. Aims. By using SINFONI, we are able to determine the spectroscopic properties of the investigated dusty infrared sources. Furthermore, we extract spatial and velocity information of these objects. We are able to identify X7, X7.1, X8, G1, DSO/G2, D2, D23, D3, D3.1, D5, and D9 in the Doppler-shifted line maps of the SINFONI H+K data. From our K-and L -band NACO data, we derive the related magnitudes of the brightest sources located west of Sgr A*. Methods. For determining the line of sight velocity information and to investigate single emission lines, we use the near-infrared integral field spectrograph SINFONI data-sets between 2005 and 2015. For the kinematic analysis, we use NACO data-sets between 2002 and 2018. This study is done in the H, K s , and L band. From the 3D SINFONI data-cubes, we extract line-maps in order to derive positional information of the sources. In the NACO images, we identify the dusty counterpart of the objects. If possible, we determine Keplerian orbits and apply a photometric analysis.Results. The spectrum of the investigated objects show a Doppler-shifted Brγ and HeI line emission. For some objects west of Sgr A*, we find additionally [Fe III] line emission that can be clearly distinguished from the background. A one-component blackbody model fits the extracted near-infrared flux for the majority of the investigated objects, with the characteristic dust temperature of 500 K. The photometric derived H-and K S -band magnitudes are between mag H > 22.5 and mag K = 18.1 +0.3 −0.8 for the dusty sources. For the H-band magnitudes we can provide an upper limit. For the bright dusty sources D2, D23, and D3, the Keplerian orbits are elliptical with a semi-major axis of a D2 = (749 ± 13) mas, a D23 = (879 ± 13), and a D3 = (880 ± 13) mas. For the DSO/G2, a single-temperature and a two-component blackbody model is fitted to the H-, K-, L -, and M-band data, while the two-component model that consists of a star and an envelope fits its SED better than an originally proposed single-temperature dusty cloud. Conclusions. The spectroscopic analysis indicates, that the investigated objects could be dust embedded pre-main-sequence stars. The Doppler-shifted [Fe III] line can be spectroscopically identified in several sources that are located between 17:45:40.05 and 17:45:42.00 in DEC. However, the sources with a DEC less than 17:45:40.05 show no [Fe III] emission. Therefore, these two groups show different spectroscopic features that could be explained by the interaction with a non-spherical outflow that originates at the position of Sgr A*. Followed by this, the hot bubble around Sgr A* consists out of isolated sources with [Fe III] line emission that can partially ...

Several publications highlight the importance of the observations of bow shocks to learn more about the surrounding interstellar medium and radiation field. We revisit the most prominent dusty and gaseous bow shock source, X7, close to the supermassive black hole, Sgr A*, using multiwavelength analysis. For the purpose of this study, we use Spectrograph for Integral Field Observations in the Near Infrared (SINFONI) (H+K-band) and NACO L′- and M′-band) data sets between 2002 and 2018 with additional COMIC/ADONIS+RASOIR (L′-band) 7 7 COME-ON-PLUS Infrared Camera/Adaptive Optics Near Infrared System + Renouveau de l’Analyseur de Surface d’Onde InfraRouge data of 1999. By analyzing the line maps of SINFONI, we identify a velocity of ∼200 km s−1 from the tip to the tail. Furthermore, a combination of the multiwavelength data of NACO and SINFONI in the H-, K-, L′-, and M′-bands results in a two-component blackbody fit that implies that X7 is a dust-enshrouded stellar object. The observed ongoing elongation and orientation of X7 in the Brγ line maps and the NACO L′-band continuum indicate a wind arising at the position of Sgr A* or at the IRS16 complex. Observations after 2010 show that the dust and the gas shell seems to be decoupled in the projection from its stellar source S50. The data also implies that the tail of X7 thermally heats up due to the presence of S50. The gas emission at the tip is excited because of the related forward scattering (Mie scattering), which will continue to influence the shape of X7 in the near future. In addition, we find excited [Fe iii] lines, which together with the recently analyzed dusty sources and the Brγ-bar underline the uniqueness of this source.

Context. The density of the ambient medium around a supermassive black hole (SMBH) and the way it varies with distance plays an important role in our understanding of the inflow-outflow mechanisms in the Galactic centre (GC). This dependence is often fitted by spherical power-law profiles based on observations in the X-ray, infrared (IR), submillimetre (submm), and radio domains. Aims. Nevertheless, the density profile is poorly constrained at the intermediate scales of 1000 Schwarzschild radii (R s). Here we independently constrain the spherical density profile using the stellar bow shock of the star S2 which orbits the SMBH at the GC with the pericentre distance of 14.4 mas (∼1500 R s). Methods. Assuming an elliptical orbit, we apply celestial mechanics and the theory of bow shocks that are at ram pressure equilibrium. We analyse the measured IR flux density and magnitudes of S2 in the L-band (3.8 micron) obtained over seven epochs in the years between 2004-2018. We put an upper limit on the emission from S2's associated putative bow shock and constrain the density profile of the ambient medium. Results. We detect no significant change in S2 flux density until the recent periapse in May 2018. The intrinsic flux variability of S2 is at the level of 2-3%. Based on the dust-extinction model, the upper limit on the number density at the S2 periapse is ∼1.87 × 10 9 cm −3 , which yields a density slope of at most 3.20. Using the synchrotron bow-shock emission, we obtain the ambient density of 1.01 × 10 5 cm −3 and a slope of 1.47. These values are consistent with a wide variety of media from hot accretion flows to potentially colder and denser media comparable in properties to broad-line-region clouds. However, a standard thin disc can be excluded at the distance of S2's pericentre. Conclusions. With the current photometry sensitivity of 0.01 mag, we are not able to make stringent constraints on the density of the ambient medium in the GC using S2-star observations. We can distinguish between hot accretion flows and thin, cold discs, where the latter can be excluded at the scale of the S2 periapse. Future observations of stars in the S cluster using instruments such as Mid-IR Extremely Large Telescope Imager and Spectrograph at Extremely Large Telescope with the photometric sensitivity of as much as 10 −3 mag will allow the GC medium to be probed at intermediate scales at densities as low as ∼700 cm −3 in case of non-thermal bow-shock emission. The new instrumentation, in combination with discoveries of stars with smaller pericentre distances, will help to independently constrain the density profile around Sagittarius A* (Sgr A*).