A Study of the NGC 6914 Star Formation Region Johanna Malinen, Marius Maskoliunas, Minja M¨Akel¨A, and Paul Anthony Wilson

Astronomy & Astrophysics manuscript no. g4˙article c ESO 2009 June 18, 2009

A study of the NGC 6914 star formation region Johanna Malinen, Marius Maskoliunas, Minja M¨akel¨a, and Paul Anthony Wilson

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Preprint online version: June 18, 2009

ABSTRACT

Aims. We have studied the star formation region NGC6914, specifically two chosen fields in the northern and southern parts. Methods. We combined near infrared, optical, and mm observations to look for manifestations of outflow activity and therefore sites of young stars. Imaging and spectroscopy was used to search for HH objects and radio observations to study the structure of the cloud. Results. We found a new Herbig-Haro object and an infrared jet. Key words. Herbig-Haro objects – NGC6914 – young stars

1. Introduction NGC 6914 is a reﬂection nebula located in the Great Cygnus Rift at a distance of approximately 1000 pc according to Racine (1968) and Shevchenko et al. (1991). It appears to be situated in the foreground of the Cygnus X region which has a distance of approximately 1.7 kpc. NGC 6914 is an active star forming area and several young stars are found in the region. Other known objects include a small reﬂection nebula PP95 (Parsamian & Petrossian 1979) and a nearby large HH object, HH 475 (Aspin & Reipurth 2000). However, the NGC 6914 region is still largely unexplored. For a review see Reipurth & Schneider (2008). The objective of this study is to explore NGC 6914 at several wavelengths. We concentrated on two areas: a region centered ′ ′ around the coordinates 20h24m31.3s, +42◦21 48” (J2000) and a region with two interesting stars, PP95 (20h24m29.6s, +42◦14 02”) ′ and V1585 Cyg (NW star) (20h24m23.3s, +42◦14 30”), about 6 arc minutes south. We call these regions the Northern and Southern region, respectively.

2. Near IR 2.1. Observations We have observed the Northern region in the near-infrared with the NOTCam instrument at NOT, La Palma, on June 10th 2009. The field of view is 4x4 arc minutes with a resolution of 0.234 arc seconds per pixel for NIR imaging. JHKs imaging was done in five frames with 5 arc second dithering and a total integration time of 3x3.6s. H2 (2.121 µm) narrowband images were done in beamswitching mode with a guide star chosen 4’ in the East-West direction and a dithering step of 10 arc seconds. The ON and OFF fields have both seven frames with a total integration time of 100s per frame. Beamswitching was used, because we were exploring extended emission, but we found that dithering could be used as the emission was not too extended. [FeII] at 1.645 µm was imaged in a 3x3 grid with a dithering step of 10 arc seconds and a total exposure time of 60s per frame. A He IC filter at 2.184 µm was used as ”off-H2” to determine if there is continuum-like emission close to the wavelength of H2, the frames were taken with the same exposure time, dithering anf grid as the [FeII] frames. Flats for all filters were taken during twilight before the observations. The seeing was ≈ 1.6 − 1.8 arc seconds during most of the observations and improving to ≈ 1.2 arc briefly before the observation run ended. An unresolved issue with the pointing was noticed after the observations: the wideband images are offset south from the narrowband images by almost an arc minute, with the narrowband images being closer to the original pointing coordinates.

2.2. Reduction The flats were reduced already at the NOT telescope. The notcam package in IRAF was used to reduce the data. The basic steps in reducing NIR data are masking the bad pixels, removing cosmic rays, sky subtraction and flat fielding. The wide- and narrow-band data were both reduced the same way. The H2 images were reduced both with using the OFF field for sky subtraction and only combining the dithered images of the ON field. The procedure for reducing beamswitched data produced a clear raster pattern on the image (most likely from incomplete masking of field stars); using the actual ON frames for measuring the sky produced better results although the dithering step was quite small (5”) for the sky subtraction. 2 Johanna Malinen et al.: A study of the NGC 6914 star formation region

h m s ◦ ′ ” Fig. 1. The Ks band image. The coordinates in the center are 20 24 31.0 , +42 21 43 (J2000), and the ﬁeld of view is 4x4 arc minutes. The bright reﬂection nebula is marked in the image.

2.3. Results There is a reflection nebula visible in the lower right hand corner in all NIR images (Figure 1). Another fainter reflection nebula is seen ≈ 0.8 arc minutes north-east from the brighter one. Both have not been seen before and indicate the presence of newborn embedded stars. We find an emission feature that is visible only in the H2 and [FeII] images (Figures 2 and 3, respectively) and not in the off-H2 (Figure 4) or JHKs filters, which suggests that the area is shocked gas. There is also a bright outflow in the top edge of the H2 image that is faintly visible in the Ks image. We have thus discovered a new bright H2 jet in this region. We attempted to make JHKs photometry with SExtractor for the stars seen in all three wideband filters and we calibrated the images, but the scatter of the stars in a (J-H) versus (H-K) diagram was large, so we used 2MASS data to construct the two-color diagram (Figure 5) for the stars in the NOTCam field. The two stars located in the Southern region, PP95 and V1585 Cyg, are also plotted in Figure 5. There are a few IR excess stars and we see that out of the two specific stars, PP95 lies outside the reddening vectors, indicating that it has excess infrared emission, and thus warm circumstellar material.

3. Optical imaging 3.1. Observations We did observations at the NOT telescope in the optical region using three filters: Hα, [SII], and I. In optical we also made ”slitless spectroscopy” by putting an R band filter in front of a grism. Images were taken using the ALFOSC 6.4’x6.4’ CCD camera. Flat field images were made during twilight before the observation run. We used three flat field frames with each filter. Using the Hα filter we made three exposures with 300 seconds exposure time each. The same was made with [SII] filter images, three exposures with 300 seconds. We imaged the I band with an exposure time of 180 seconds. Also we made three images using a combination of a R filter and a grism with an exposure time of 600 seconds each.

3.2. Reduction The optical image reduction was made using IRAF. We combined ten bias images into a master bias. It is an average of all bias images and we use it to remove CCD additive effects from flat field and observed images. Then the flat frame images have been corrected with the master bias, and we combined them to the master flats. The master flat for each filter was made from three flat field images. Observed images were corrected with master flat frames separately, and after this we combined them to final images. Eventually we have a reduced image for each of the filters (Hα, [SII], I and R with a grism). Johanna Malinen et al.: A study of the NGC 6914 star formation region 3

h m s ◦ ′ ” Fig. 2. The H2 band image. The coordinates in the center are 20 24 31.0 , +42 21 43 (J2000), and the ﬁeld of view is 4x4 arc minutes. The outﬂows we found are marked in the images.

′ Fig. 3. The [FeII] band image. The coordinates in the center are 20h24m31.0s, +42◦21 43” (J2000), and the field of view is 4x4 arc minutes. Two reflection nebulae seen in all filters are marked in the image. 4 Johanna Malinen et al.: A study of the NGC 6914 star formation region

′ Fig. 4. The He band image. The coordinates in the center are 20h24m31.0s, +42◦21 43.2” (J2000), and the ﬁeld of view is 4x4 arc minutes.

Fig. 5. A (J-H) versus (H-K) diagram made from 2MASS stars in the NOTCam ﬁeld. The asterisk symbols mark stars that have 2MASS photometric quality better than BBB (i.e. the uncertainty for the JHKs magnitude is smaller than 0.155 in all three bands), crosses are other stars in the ﬁeld with worse photometric quality. The colors of the stars PP95 and V1585 Cyg that lie in the Southern region are also plotted. Reddening vectors are from (Indebetouw et al. 2005).

3.3. Results The main point in our optical wavelength investigation was to detect Hα emission stars and Herbig-Haro objects. One way to do that is to compare images made at different wavelengths. For detection of Herbig-Haro objects we used [SII], Hα and I filters (Figures 7, 8, and 9, respectively). In I filter there is usually a small amount of continuum emission. We look how images from different filters appear. If an object appears in all three images it cannot be a Herbig-Haro object which are pure emission line objects. Comparing Johanna Malinen et al.: A study of the NGC 6914 star formation region 5

Fig. 6. A cropped grism+R band ﬁlter image of the new Hα star we have found.

′ Fig. 7. The [SII] band image. The coordinates in the center are 20h24m31.0s, +42◦21 43” (J2000), and the field of view is 4x4 arc minutes. There were some cirrus clouds in the sky during the observations, and therefore we do not have an optimal image quality. these images we notice an emission area on the [SII] image. We have thus discovered a new Herbig-Haro object. The coordinates ′ of this object are approximately 20h24m36s, +42◦21 08”. We investigated reduced images made with an R filter in front of a grism and find two interesting stars; one is definitely an Hα ′ emission star with coordinates 20h24m40s, +42◦21 08” (Figure 6), and the other we can only speculate is an Hα emission star.

4. Optical spectroscopy 4.1. Observations Low resolution spectra of the stars PP95 and V1585 Cyg were taken using the NOT telescope together with the ALFOSC Spectrograph 1. The dispersed spectrum was made using Grism #7 and a 1” slit. The exposures taken were each 1800s.

4.2. Reduction The spectra were reduced using IRAF (Image Reduction and Analysis Facility). After removing the detector signature and pixel gain variations using flat-fields, a background correction was done. The image background was fitted and subtracted from the spectra, both removing emission lines from Earths atmosphere but also giving cleaner spectra. The spectrum was extracted using the apall task in iraf. It was later wavelength calibrated and flux calibrated.

1 The data presented here have been taken using ALFOSC, which is owned by the Instituto de Astroﬁsica de Andalucia (IAA) and operated at the Nordic Optical Telescope under agreement between IAA and the NBIfAFG of the Astronomical Observatory of Copenhagen 6 Johanna Malinen et al.: A study of the NGC 6914 star formation region

′ Fig. 8. The Hα band image. The coordinates in the center are 20h24m31.0s, +42◦21 43” (J2000), and the ﬁeld of view is 4x4 arc minutes.

′ Fig. 9. The I band image. The coordinates in the center are 20h24m31.0s, +42◦21 43” (J2000), and the ﬁeld of view is 4x4 arc minutes. Johanna Malinen et al.: A study of the NGC 6914 star formation region 7

Fig. 10. Spectrum of the PP95 star, which indicates that it is a Herbig Ae/Be type star.

Fig. 11. Spectrum of the NW star showing its hydrogen Balmer lines and an abundance of metallic lines. The NaI aborption is also prominent which likely indicates interstellar absorption.

4.3. Results The spectra are both consistent with the stars we expect to ﬁnd in NGC6914. The NW star (V1585 Cyg) is a solar type young star which is eithera late F typeor an early G typestar based on th presence of metallic lines in the G-band (higher resolution spectra are needed to more accurately determine the spectral class). The PP95 star is found to be a Herbig Ae/Be star, because of the presence of strong absorption in the higher Balmer lines (Halpha is in strong emission).

5. Radio astronomy 5.1. Observations Single dish mm observations were performed in remote mode with the OSO 20 m radio telescope. Our own CS-observations of the ′ Northern region around 20h24m31.3s, +42◦21 48.0” were noisy because of bad weather and therefore they could not be used. We used backup data of 12CO (1-0) with frequency 115GHz of a 132” x 100” area in the Southern region centered on PP95 ′ (20h24m39.6s, +42◦14 02.0”). Observations were performed using frequency switching with 20 MHz switch, 63 (7 x 9) pointings, 32” beam, 16” spacing (Nyquist sampled) and 4380s total integration time. Intensity of the data was approximately 8K and the rms approximately 0.8K giving a S/N of 10. 8 Johanna Malinen et al.: A study of the NGC 6914 star formation region

Fig. 12. An example spectrum of PP95 area showing two closeby lines.

5.2. Reduction We reduced the mm data with the XS reduction program. We averaged the spectra in order to increase the S/N ratio and ﬁtted the baseline with a 3rd order polynomial and removed it. Then we folded the scans and smoothed the spectra by decreasing the resolution. An example spectrum is given in Figure 12. It shows two closeby lines with velocities between 0 and 7 km/s. We calculated intensity maps and velocity-position maps separately for both lines.

5.3. Results The intensity map of the weaker first line in Figure 13 shows a CO cloud next to PP95. The contour levels were drawn every 3 σ = 5Kkm/s. The intensity map of the stronger second line in Figure 14 shows a wide spread CO cloud. The contour levels of this map were drawn every 3 σ = 6Kkm/s. The PP95 star has apparently pushed the CO gas around it leaving a sparser area in the middle. The velocity-position map for the first line in Figure 15 shows that the cloud has a constant velocity of approximately 5 km/s. The velocity-position map for the second line is similar with approximately the same velocity. Thus we do not find any evidencefor a molecular outflow.

6. Conclusions

We have discovered a previously unknown Herbig-Haro object and an associated H2 outflow in the NGC6914 area; both are indica- tive of nearby star formation. Herbig-Haro objects are typically regions of shocked gas with specific atomic emission lines, and the emission line ratios can be used to derive physical properties of the gas (e.g. electron density). The fact that our new HH object primarily shows up in the [SII] image indicates that it is a relatively weak shock. The outflow was discovered in the H2 filter and also faintly seen in the Ks filter. The detection in [SII] and Hα supports the conclusion that the emission features detected in near infrared (H2 and [FeII]) are indeed HH objects. The PP95 star that was observed in 12CO(1-0) has infrared excess, suggesting that it is a young stellar object. The slitless spectroscopy showed that the Northern region contains two Hα stars which very likely are new T Tauri stars.

Acknowledgements. We would like to thank our project leader Bo Reipurth, and Johannes Andersen and Raine Karjalainen for organising the NordForsk Summer School 2009.

References Aspin, C. & Reipurth, B. 2000 MNRAS, 311, 522 Indebetouw, R. et al. ApJ, 619: 931, 2005 Parsamian, E.S. & Petrossian, V.M. 1979 Soobscheniya Byurakan Obs., 51, 3 Racine, R. 1968, AJ, 73, 233 Reipurth, B., & Schneider, N. 2008 Star Formation and Young Clusters in Cygnus, in Handbook of Star Forming Regions Vol. I, Astronomical Society of the Pasiﬁc Shevchenko, V.S., Ibragimov, M.A., & Chernysheva, T.L. 1991 Sov. Astron., 35, 229 Johanna Malinen et al.: A study of the NGC 6914 star formation region 9

Fig. 13. Intensity map of the ﬁrst line in PP95 region.

Fig. 14. Intensity map of the second line in PP95 region. Apparently the young star has pushed the molecular material away, so it is located in a low-density cavity. 10 Johanna Malinen et al.: A study of the NGC 6914 star formation region

Fig. 15. Velocity-position map for the ﬁrst line. No indication for a high-velocity molecular outﬂow is seen.